Updated on 2024/04/22

写真a

 
NAKAZATO, Hiromichi
 
Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Professor
Degree
(BLANK) ( 早稲田大学 )

Research Experience

  • 2000
    -
     

    Waseda University, Professor

  • 1995
    -
    2000

    Waseda University, Associate Professor

  • 1987
    -
    1995

    University of the Ryukyus, Research Assistant

  • 1985
    -
    1987

    Waseda University, Research Assistant

Education Background

  •  
    -
    1985

    Waseda University   Graduate School, Division of Science and Engineering  

  •  
    -
    1980

    Waseda University   Faculty of Science and Engineering  

Professional Memberships

  •  
     
     

    アメリカ物理学会

  •  
     
     

    日本物理学会

Research Areas

  • Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Research Interests

  • Elementary Particles Physics,Nuclear Physics & Cosmic Ray Physics,Physical Properties in General(incl. Basic Theories)

 

Papers

  • Characterization of Quantum and Classical Critical Points for an Integrable Two-Qubit Spin–Boson Model

    Roberto Grimaudo, Antonino MESSINA, Hiromichi Nakazato, Alessandro SERGI, Davide Valenti

    Symmetry    2023.12

    DOI

    Scopus

  • Invariant-Parameterized Exact Evolution Operator for SU(2) Systems with Time-Dependent Hamiltonian

    Hiromichi Nakazato, Alessandro Sergi, Agostino Migliore, Antonino Messina

    ENTROPY   25 ( 1 )  2023.01  [Refereed]

     View Summary

    We report the step-by-step construction of the exact, closed and explicit expression for the evolution operator U(t) of a localized and isolated qubit in an arbitrary time-dependent field, which for concreteness we assume to be a magnetic field. Our approach is based on the existence of two independent dynamical invariants that enter the expression of SU(2) by means of two strictly related time-dependent, real or complex, parameters. The usefulness of our approach is demonstrated by exactly solving the quantum dynamics of a qubit subject to a controllable time-dependent field that can be realized in the laboratory. We further discuss possible applications to any SU(2) model, as well as the applicability of our method to realistic physical scenarios with different symmetry properties.

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • Exact master equation for an open Jaynes-Cummings system

    Akane Watanabe, Hiromichi Nakazato

    ANNALS OF PHYSICS   441  2022.06  [Refereed]

     View Summary

    A master equation for the Jaynes-Cummings (JC) system interacting with a bosonic reservoir through a conserved quantity is derived analytically without any approximation. The derivation is valid for any initial JC state that has no correlation with the initial reservoir at any temperature and yields a Gorini-Kossakowski- Lindblad-Sudarshan-type master equation with time-dependent coefficients. Several physical quantities of the open JC system are examined and the validity or limit of some of the standard approximations used to derive the master equation is discussed on the basis of the exact results obtained here. (C) 2022 The Authors. Published by Elsevier Inc.

    DOI

    Scopus

  • Generalized adiabatic impulse approximation

    Takayuki Suzuki, Hiromichi Nakazato

    Physical Review A   105 ( 2 ) 022211 (14 pages)  2022.02  [Refereed]

    Authorship:Last author

    DOI

  • Analytic approach to dynamics of the resonant and off-resonant Jaynes-Cummings systems with cavity losses

    Soshun Ozaki, Hiromichi Nakazato

    Physical Review A   103 ( 5 ) 053713 (11 pages)  2021.05  [Refereed]

    DOI

  • Kolmogorov-Arnold-Moser--stability for conserved quantities in finite-dimensional quantum systems

    Daniel Burgarth, Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa

    Physical Review Letters   126 ( 15 ) 150401 (6 pages)  2021.04  [Refereed]

    DOI

  • Eternal adiabaticity in quantum evolution

    Daniel Burgarth, Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa

    Physical Review A   103 ( 3 ) 032214 (23 pages)  2021.03  [Refereed]

    DOI

  • Quantum Zeno Dynamics from General Quantum Operations

    Daniel Burgarth, Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa

    Quantum   4   289 - 289  2020.07  [Refereed]

     View Summary

    We consider the evolution of an arbitrary quantum dynamical semigroup of a finite-dimensional quantum system under frequent kicks, where each kick is a generic quantum operation. We develop a generalization of the Baker-Campbell-Hausdorff formula allowing to reformulate such pulsed dynamics as a continuous one. This reveals an adiabatic evolution. We obtain a general type of quantum Zeno dynamics, which unifies all known manifestations in the literature as well as describing new types.

    DOI

  • Dzyaloshinskii-Moriya and dipole-dipole interactions affect coupling-based Landau-Majorana-St\"uckelberg-Zener transitions

    Roberto Grimaudo, Hiromichi Nakazato, Antonino Messina, Nikolay V. Vitanov

    Physical Review Research   2 ( 43 ) 033092 (9 pages)  2020.07  [Refereed]

  • Bounds on mixed state entanglement

    Leggio, B., Napoli, A., Nakazato, H., Messina, A.

    Entropy   22 ( 1 ) 62 - 62  2020.01  [Refereed]

    DOI

    Scopus

    6
    Citation
    (Scopus)
  • Generalized adiabatic theorem and strong-coupling limits

    Burgarth, D., Facchi, P., Nakazato, H., Pascazio, S., Yuasa, K.

    Quantum   3   152 (23 pages)  2019.06  [Refereed]

    DOI

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    30
    Citation
    (Scopus)
  • Analytically solvable 2×2 PT -symmetry dynamics from su(1,1)-symmetry problems ANALYTICALLY SOLVABLE 2×2 PT- SYMMETRY ... R. GRIMAUDO et al.

    Grimaudo, R., De Castro, A.S.M., Nakazato, H., Messina, A.

    Physical Review A   99 ( 5 ) 052103-1 - 052103-7  2019.05  [Refereed]

    DOI

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    11
    Citation
    (Scopus)
  • Experimental Investigation of Quantum Decay at Short, Intermediate, and Long Times via Integrated Photonics

    Crespi, A., Pepe, F.V., Facchi, P., Sciarrino, F., Mataloni, P., Nakazato, H., Pascazio, S., Osellame, R.

    Physical Review Letters   122 ( 13 ) 130401-1 - 130401-6  2019.04  [Refereed]

    DOI

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    31
    Citation
    (Scopus)
  • Analytic estimation of transition between instantaneous eigenstates of quantum two-level system

    Suzuki, T., Nakazato, H., Grimaudo, R., Messina, A.

    Scientific Reports   8 ( 1 ) 17433 (7 pages)  2018.11  [Refereed]

    DOI PubMed

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    10
    Citation
    (Scopus)
  • Classes of Exactly Solvable Generalized Semi-Classical Rabi Systems

    Grimaudo, R., Magalh{\~a}es de Castro, A.S., Nakazato, H., Messina, A.

    Annalen der Physik   530 ( 12 ) 1800198 (8 pages)  2018.11  [Refereed]

    DOI

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    23
    Citation
    (Scopus)
  • Time evolution of a pair of distinguishable interacting spins subjected to controllable and noisy magnetic fields

    R. Grimaudo, Yu. Belousov, H. Nakazato, A. Messina

    Annals of Physics   392   242 - 259  2018.05  [Refereed]

     View Summary

    The quantum dynamics of a Jˆ2=(jˆ1+jˆ2)2-conserving Hamiltonian model describing two coupled spins jˆ1 and jˆ2 under controllable and fluctuating time-dependent magnetic fields is investigated. Each eigenspace of Jˆ2 is dynamically invariant and the Hamiltonian of the total system restricted to any one of such (j1+j2)−|j1−j2|+1 eigenspaces, possesses the SU(2) structure of the Hamiltonian of a single fictitious spin acted upon by the total magnetic field. We show that such a reducibility holds regardless of the time dependence of the externally applied field as well as of the statistical properties of the noise, here represented as a classical fluctuating magnetic field. The time evolution of the joint transition probabilities of the two spins jˆ1 and jˆ2 between two prefixed factorized states is examined, bringing to light peculiar dynamical properties of the system under scrutiny. When the noise-induced non-unitary dynamics of the two coupled spins is properly taken into account, analytical expressions for the joint Landau–Zener transition probabilities are reported. The possibility of extending the applicability of our results to other time-dependent spin models is pointed out.

    DOI

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    17
    Citation
    (Scopus)
  • Completeness of scattering states of the Dirac Hamiltonian with a step potential

    Ochiai, M., Nakazato, H.

    Journal of Physics Communications   2 ( 1 ) 015006 (16 pages)  2018.01  [Refereed]

    Authorship:Last author

    DOI

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    2
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    (Scopus)
  • An example of interplay between Physics and Mathematics: Exact resolution of a new class of Riccati Equations

    L. A. Markovich, R. Grimaudo, A. Messina, H. Nakazato

    ANNALS OF PHYSICS   385   522 - 531  2017.10  [Refereed]

     View Summary

    A novel recipe for exactly solving in finite terms a class of special differential Riccati equations is reported. Our procedure is entirely based on a successful resolution strategy quite recently applied to quantum dynamical time-dependent SU(2) problems. The general integral of exemplary differential Riccati equations, not previously considered in the specialized literature, is explicitly determined to illustrate both mathematical usefulness and easiness of applicability of our proposed treatment. The possibility of exploiting the general integral of a given differential Riccati equation to solve an SU(2) quantum dynamical problem, is succinctly pointed out. (C) 2017 Elsevier Inc. All rights reserved.

    DOI

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    20
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    (Scopus)
  • Synchronizing quantum harmonic oscillators through two-level systems

    Benedetto Militello, Hiromichi Nakazato, Anna Napoli

    PHYSICAL REVIEW A   96 ( 2 ) 023862 (8 pages)  2017.08  [Refereed]

     View Summary

    Two oscillators coupled to a two-level system which in turn is coupled to an infinite number of oscillators (reservoir) are considered, bringing to light the occurrence of synchronization. A detailed analysis clarifies the physical mechanism that forces the system to oscillate at a single frequency with a predictable and tunable phase difference. Finally, the scheme is generalized to the case of N oscillators and M(< N) two-level systems.

    DOI

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    18
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    (Scopus)
  • Lindbladian purification

    Christian Arenz, Daniel Burgarth, Vittorio Giovannetti, Hiromichi Nakazato, Kazuya Yuasa

    Quantum Science and Technology   2 ( 2 ) 024001 (10 pages)  2017.06  [Refereed]

     View Summary

    In a recent work (Burgarth et al 2014, Nat. Commun. 5 5173), it was shown that a series of frequent measurements can project the dynamics of a quantum system onto a subspace in which the dynamics can be more complex. In this subspace, even full controllability can be achieved, although the controllability over the system before the projection is very poor since the control Hamiltonians commute with each other. We can also think of the opposite: any Hamiltonians of a quantum system, which are in general noncommutative with each other, can be made commutative by embedding them in an extended Hilbert space, thus the dynamics in the extended space becomes trivial and simple. This idea of making noncommutative Hamiltonians commutative is called 'Hamiltonian purification.' The original noncommutative Hamiltonians are recovered by projecting the system back onto the original Hilbert space through frequent measurements. Here, we generalise this idea to open-system dynamics by presenting a simple construction to make Lindbladians, as well as Hamiltonians, commutative on a larger space with an auxiliary system. We show that the original dynamics can be recovered through frequently measuring the auxiliary system in a non-selective way. Moreover, we provide a universal pair of Lindbladians that describe an 'accessible' open quantum system for generic system sizes. This allows us to conclude that through a series of frequent non-selective measurements a nonaccessible open quantum system generally becomes accessible. This sheds further light on the role of measurement backaction on the control of quantum systems.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Can Decay Be Ascribed to Classical Noise?

    Daniel Burgarth, Paolo Facchi, Giancarlo Garnero, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa

    OPEN SYSTEMS & INFORMATION DYNAMICS   24 ( 1 ) 1750001 (18 pages)  2017.03  [Refereed]

    DOI

    Scopus

    9
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    (Scopus)
  • Exactly solvable time-dependent models of two interacting two-level systems

    Grimaudo, R., Messina, A., Nakazato, H.

    Physical Review A   94 ( 2 ) 022108 (13 pages)  2016.08  [Refereed]

     View Summary

    © 2016 American Physical Society.Two coupled two-level systems placed under external time-dependent magnetic fields are modeled by a general Hamiltonian endowed with a symmetry that enables us to reduce the total dynamics into two independent two-dimensional subdynamics. Each of the subdynamics is shown to be brought into an exactly solvable form by appropriately engineering the magnetic fields and thus we obtain an exact time evolution of the compound system. Several physically relevant and interesting quantities are evaluated exactly to disclose intriguing phenomena in such a system.

    DOI

    Scopus

    31
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  • Universal control induced by noise

    Arenz, C., Burgarth, D., Facchi, P., Giovannetti, V., Nakazato, H., Pascazio, S., Yuasa, K.

    Physical Review A   93 ( 6 ) 062308 (10 pages)  2016.06  [Refereed]

     View Summary

    © 2016 American Physical Society.On the basis of the quantum Zeno effect, it has been recently shown [D. K. Burgarth, Nat. Commun. 5, 5173 (2014)2041-172310.1038/ncomms6173] that a strong-amplitude-damping process applied locally on a part of a quantum system can have a beneficial effect on the dynamics of the remaining part of the system. Quantum operations that cannot be implemented without the dissipation become achievable by the action of the strong dissipative process. Here we generalize this idea by identifying decoherence-free subspaces (DFSs) as the subspaces in which the dynamics becomes more complex. Applying methods from quantum control theory, we characterize the set of reachable operations within the DFSs. We provide three examples that become fully controllable within the DFSs while the control over the original Hilbert space in the absence of dissipation is trivial. In particular, we show that the (classical) Ising Hamiltonian is turned into a Heisenberg Hamiltonian by strong collective decoherence, which provides universal quantum computation within the DFSs. Moreover, we perform numerical gate optimization to study how the process fidelity scales with the noise st

    DOI

    Scopus

    11
    Citation
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  • Photon distribution at the output of a beam splitter for imbalanced input states

    Nakazato, H., Pascazio, S., Stobi?ska, M., Yuasa, K.

    Physical Review A   93 ( 2 ) 023845 (6 pages)  2016.02  [Refereed]

     View Summary

    © 2016 American Physical Society.In the Hong-Ou-Mandel interferometric scheme, two identical photons that illuminate a balanced beam splitter always leave through the same exit port. Similar effects have been predicted and (partially) experimentally confirmed for multiphoton Fock-number states. In the limit of large photon numbers, the output distribution follows a (1-x2)-1/2 law, where x is the normalized imbalance in the output photon numbers at the two output ports. We derive an analytical formula that is also valid for imbalanced input photon numbers with a large total number of photons, and focus on the extent to which the hypothesis of perfect balanced input can be relaxed, discussing the robustness and universal features of the output distribution.

    DOI

    Scopus

    6
    Citation
    (Scopus)
  • Hamiltonian purification

    Davide Orsucci, Daniel Burgarth, Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa, Vittorio Giovannetti

    JOURNAL OF MATHEMATICAL PHYSICS   56 ( 12 ) 122104 (21 pages)  2015.12  [Refereed]

     View Summary

    The problem of Hamiltonian purification introduced by Burgarth et al. [Nat. Commun. 5, 5173 (2014)] is formalized and discussed. Specifically, given a set of noncommuting Hamiltonians {h(1),..., h(m)} operating on a d-dimensional quantum system H-d, the problem consists in identifying a set of commuting Hamiltonians {H-1,..., H-m} operating on a larger d(E)-dimensional system H-dE which embeds Hd as a proper subspace, such that h(j) = PHjP with P being the projection which allows one to recover Hd from HdE. The notions of spanning-set purification and generator purification of an algebra are also introduced and optimal solutions for u(d) are provided. (C) 2015 AIP Publishing LLC.

    DOI

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    6
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  • Phase randomization and typicality in the interference of two condensates

    Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Francesco V. Pepe, Golam Ali Sekh, Kazuya Yuasa

    INTERNATIONAL JOURNAL OF QUANTUM INFORMATION   12 ( 7-8 ) 1560019 (15 pages)  2014.11  [Refereed]

     View Summary

    Interference is observed when two independent Bose-Einstein condensates expand and overlap. This phenomenon is typical, in the sense that the overwhelming majority of wave functions of the condensates, uniformly sampled out of a suitable portion of the total Hilbert space, display interference with maximal visibility. We focus here on the phases of the condensates and their (pseudo) randomization, which naturally emerges when two-body scattering processes are considered. Relationship to typicality is discussed and analyzed.

    DOI

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    3
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  • Analytically solvable Hamiltonians for quantum two-level systems and their dynamics

    A. Messina, H. Nakazato

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   47 ( 44 ) 445302 (10 pages)  2014.11  [Refereed]

     View Summary

    A simple systematic way of obtaining analytically solvable Hamiltonians for quantum two-level systems is presented. In this method, a time-dependent Hamiltonian and the resulting unitary evolution operator are connected through an arbitrary function of time, furnishing us with new analytically solvable cases. The method is surprisingly simple, direct, and transparent and is applicable to a wide class of two-level Hamiltonians with no involved constraint on the input function. A few examples illustrate how the method leads to simple solvable Hamiltonians and dynamics.

    DOI

    Scopus

    43
    Citation
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  • Exponential rise of dynamical complexity in quantum computing through projections

    Daniel Klaus Burgarth, Paolo Facchi, Vittorio Giovannetti, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa

    NATURE COMMUNICATIONS   5   5173 (6 pages)  2014.10  [Refereed]

     View Summary

    The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once 'observed' as outlined above. Conversely, we show that any complex quantum dynamics can be 'purified' into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics.

    DOI PubMed

    Scopus

    36
    Citation
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  • Measurement of Purity, the Simplest Nonlinear Functional of the Density Matrix

    Tohru Tanaka, Hiromichi Nakazato

    OPEN SYSTEMS & INFORMATION DYNAMICS   21 ( 1-2 ) 1440009 (27 pages)  2014.06  [Refereed]

     View Summary

    After reviewing the earlier ideas to measure the purity of a quantum system, a new scheme for the measurement of purity is presented, which aims at providing a simple, direct and efficient procedure without resorting to quantum state tomography. The scheme is also illustrated in the Bloch-vector representation for a two-level quantum system (qubit) and for a general D-level quantum system. As a variant, a simple example implemented in a one-dimensional scattering process to measure the purity of the target qubit is also given.

    DOI

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    1
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  • Interference in a two-mode Bose system as a typical phenomenon

    Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Francesco V. Pepe, Kazuya Yuasa

    PHYSICAL REVIEW A   89 ( 6 ) 063625 (9 pages)  2014.06  [Refereed]

     View Summary

    When a Bose-Einstein condensate is divided into two parts that are subsequently released and overlap, interference fringes are observed. We show here that this interference is typical, in the sense that most wave functions of the condensate, randomly sampled out of a suitable ensemble, display interference. We make no hypothesis of decoherence between the two parts of the condensate.

    DOI

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    4
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  • Determining eigenvalues of a density matrix with minimal information in a single experimental setting

    Tohru Tanaka, Yukihiro Ota, Mitsunori Kanazawa, Gen Kimura, Hiromichi Nakazato, Franco Nori

    PHYSICAL REVIEW A   89 ( 1 ) 012117 (4 pages)  2014.01  [Refereed]

     View Summary

    Eigenvalues of a density matrix characterize well the quantum state's properties, such as coherence and entanglement. We propose a simple method to determine all the eigenvalues of an unknown density matrix of a finite-dimensional system in a single experimental setting. Without fully reconstructing a quantum state, eigenvalues are determined with the minimal number of parameters obtained by a measurement of a single observable. Moreover, its implementation is illustrated in linear optical and superconducting systems.

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    17
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  • Non-Abelian phases from quantum Zeno dynamics

    Daniel Burgarth, Paolo Facchi, Vittorio Giovannetti, Hiromichi Nakazato, Saverio Pascazio, Kazuya Yuasa

    Physical Review A - Atomic, Molecular, and Optical Physics   88 ( 4 ) 042107 (5 pages)  2013.10  [Refereed]

     View Summary

    A connection is established between the non-Abelian phases obtained via adiabatic driving and those acquired via quantum Zeno dynamics induced by repeated projective measurements. In comparison to the adiabatic case, the Zeno dynamics is shown to be more flexible in tuning the system evolution, which paves the way for the implementation of unitary quantum gates and applications in quantum control. © 2013 American Physical Society.

    DOI

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    12
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  • A Controlled-NOT Gate in a Chain of Qubits Embedded in a Spin Field-Effect Transistor and Its Process Tomography

    Makoto Unoki, Hiromichi Nakazato, Kazuya Yuasa, Kanji Yoh

    The European Physical Journal B   86   393  2013.09  [Refereed]

    DOI

  • Possibility of a minimal purity-measurement scheme critically depends on the parity of dimension of the quantum system

    T. Tanaka, G. Kimura, H. Nakazato

    Physical Review A - Atomic, Molecular, and Optical Physics   87 ( 1 ) 012303 (8 pages)  2013.01  [Refereed]

     View Summary

    In this paper, we investigate the possibility of measuring the purity of a quantum state (and the overlap between two quantum states) within a minimal model where the measurement device is minimally composed. The minimality is based on the assumptions that (i) we use a yes-no measurement on a single system to determine the single value of the purity in order not to extract other redundant information and (ii) we use neither ancilla nor random measurement. We show that the measurability of the purity within this model critically depends on the parity of dimension of the quantum system: The purity measurement is possible for odd-dimensional quantum systems, while it is impossible for even-dimensional cases. © 2013 American Physical Society.

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    15
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  • Measurement scheme for purity based on two two-body gates

    H. Nakazato, T. Tanaka, K. Yuasa, G. Florio, S. Pascazio

    PHYSICAL REVIEW A   85 ( 4 ) 042316 (7 pages)  2012.04  [Refereed]

     View Summary

    A scheme for measuring the purity of a quantum system with a finite number of levels is presented. The method makes use of two root SWAP gates and hinges only on measurements performed on a reference system, prepared in a certain pure state and coupled with the target system. Neither tomographic methods, with the complete reconstruction of the state, nor interferometric setups are needed.

    DOI

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    19
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  • HEAT CAPACITY AND ENTANGLEMENT MEASURE IN A SIMPLE TWO-QUBIT MODEL

    B. Leggio, A. Napoli, H. Nakazato, A. Messina

    JOURNAL OF RUSSIAN LASER RESEARCH   32 ( 4 ) 362 - 371  2011.07  [Refereed]

     View Summary

    A simple two-qubit model showing quantum phase transitions as a consequence of ground-state-level crossings is studied in detail. Using the system's concurrence as an entanglement measure and heat capacity as a marker of thermodynamical properties, we obtain an analytical expression giving the latter in terms of the former. A protocol allowing an experimental measure of entanglement is then presented and compared with a related proposal recently reported by Wiesniak, Vedral, and Brukner.

    DOI

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    2
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  • Dissipative effects on a generation scheme of a W state in an array of coupled Josephson junctions

    R. Migliore, M. Scala, A. Napoli, K. Yuasa, H. Nakazato, A. Messina

    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS   44 ( 7 )  2011.04  [Refereed]

     View Summary

    The dynamics of an open quantum system, consisting of three superconducting qubits interacting with independent reservoirs, is investigated to elucidate the effects of the environment on a unitary generation scheme of W states (Migliore R et al 2006 Phys. Rev. B 74 104503). To this end a microscopic master equation is constructed and its exact resolution predicts the generation of a Werner-like state instead of the W state. A comparison between our model and a more intuitive phenomenological model is also considered, in order to find the limits of the latter approach in the case of structured reservoirs.

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    11
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  • Distillation by repeated measurements: Continuous spectrum case

    Bruno Bellomo, Giuseppe Compagno, Hiromichi Nakazato, Kazuya Yuasa

    Physical Review A - Atomic, Molecular, and Optical Physics   82 ( 6 )  2010.12  [Refereed]

     View Summary

    Repeated measurements on one part of a bipartite system strongly affect the other part that is not measured, the dynamics of which is regulated by an effective contracted evolution operator. When the spectrum of this operator is discrete, the nonmeasured system is driven into a pure state, irrespective of the initial state, provided that the spectrum satisfies certain conditions. We show here that, even in the case of continuous spectrum, an effective distillation can occur under rather general conditions. We confirm it by applying our formalism to a simple model. © 2010 The American Physical Society.

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    3
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  • Spectral resolution of the Liouvillian of the Lindblad master equation for a harmonic oscillator

    Daigo Honda, Hiromichi Nakazato, Motoyuki Yoshida

    JOURNAL OF MATHEMATICAL PHYSICS   51 ( 7 ) 072107  2010.07  [Refereed]

     View Summary

    A Lindblad master equation for a harmonic oscillator, which describes the dynamics of an open system, is formally solved. The solution yields the spectral resolution of the Liouvillian, that is, all eigenvalues and eigenprojections are obtained. This spectral resolution is discussed in depth in the context of the biorthogonal system and the rigged Hilbert space, and the contribution of each eigenprojection to expectation values of physical quantities is revealed. We also construct the ladder operators of the Liouvillian, which clarify the structure of the spectral resolution. (C) 2010 American Institute of Physics. [doi:10.1063/1.3442363]

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  • Entanglement Generation by a Three-Dimensional Qubit Scattering: Concurrence vs. Path (In)Distinguishability

    Yasser Omar, Yuichiro Hida, Hiromichi Nakazato, Kazuya Yuasa

    QUANTUM COMMUNICATION AND QUANTUM NETWORKING   36   17 - +  2010  [Refereed]

     View Summary

    A scheme for generating an entangled state in a two spin-1/2 system by means of a spin-dependent potential scattering of another qubit is presented and analyzed in three dimensions. The entanglement is evaluated in terms of the concurrence both at the lowest and in full order in perturbation with an appropriate renormalization for the latter, and its characteristics are discussed in the context of (in)distinguishability of alternative paths for a quantum particle.

    DOI

  • Efficient generation of a maximally entangled state by repeated on- and off-resonant scattering of ancilla qubits

    Kazuya Yuasa, Daniel Burgarth, Vittorio Giovannetti, Hiromichi Nakazato

    NEW JOURNAL OF PHYSICS   11  2009.12  [Refereed]

     View Summary

    A scheme for preparing two fixed noninteracting qubits in a maximally entangled state is presented. By repeating on-and off-resonant scattering of ancilla qubits, the target qubits are driven from an arbitrary initial state into a singlet state with probability 1 (perfect efficiency). Neither the preparation nor the post-selection of the ancilla spin state is required. The convergence from an arbitrary input state to the unique fixed point (mixing property) is proved rigorously, and its robustness is investigated by scrutinizing the effects of imperfections in the incident wave of the ancillasuch as mistuning to a resonant momentum, imperfect monochromatization, and fluctuation of the incident momentum-as well as detector efficiency.

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    19
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  • Extraction of a squeezed state in a field mode via repeated measurements on an auxiliary quantum particle

    Bruno Bellomo, Giuseppe Compagno, Hiromichi Nakazato, Kazuya Yuasa

    PHYSICAL REVIEW A   80 ( 5 )  2009.11  [Refereed]

     View Summary

    The dynamics of a system, consisting of a particle initially in a Gaussian state interacting with a field mode, under the action of repeated measurements performed on the particle, is examined. It is shown that regardless of its initial state the field is distilled into a squeezed state. The dependence on the physical parameters of the dynamics is investigated.

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • State tomography of a qubit through scattering of a probe qubit

    Antonella De Pasquale, Kazuya Yuasa, Hiromichi Nakazato

    PHYSICAL REVIEW A   80 ( 5 )  2009.11  [Refereed]

     View Summary

    We discuss the state tomography of a fixed qubit (a spin-1/2 target particle), which is in general in a mixed state, through one-dimensional scattering of a probe qubit off the target. Two strategies are presented by making use of different degrees of freedom of the probe, i.e. spin and momentum. Remarkably, the spatial degree of freedom of the probe can be utilized for optimizing the tomographic schemes.

    DOI

    Scopus

    8
    Citation
    (Scopus)
  • THWARTED DYNAMICS BY PARTIAL PROJECTIVE MEASUREMENTS

    Bruno Bellomo, Giuseppe Compagno, Hiromichi Nakazato, Kazuya Yuasa

    JOURNAL OF RUSSIAN LASER RESEARCH   30 ( 5 ) 451 - 457  2009.09  [Refereed]

     View Summary

    The dynamics of a system made of a particle interacting with a field mode "thwarted" by the action of repeated projective measurements on the particle is examined. The effect of the partial measurements is discussed by comparing it with the dynamics in the absence of the measurements.

    DOI CiNii

    Scopus

    1
    Citation
    (Scopus)
  • Entanglement generation by qubit scattering in three dimensions

    Yuichiro Hida, Hiromichi Nakazato, Kazuya Yuasa, Yasser Omar

    PHYSICAL REVIEW A   80 ( 1 )  2009.07  [Refereed]

     View Summary

    A qubit (a spin-1/2 particle) prepared in the up state is scattered by local spin-flipping potentials produced by the two target qubits (two fixed spins), both prepared in the down state, to generate an entangled state in the latter when the former is found in the down state after scattering. The scattering process is analyzed in three dimensions, both to lowest order and in full order in perturbation, with an appropriate renormalization for the latter. The entanglement is evaluated in terms of the concurrence as a function of the incident and scattering angles, the size of the incident wave packet, and the detector resolution to clarify the key elements for obtaining an entanglement with high quality. The characteristics of the results are also discussed in the context of (in)distinguishability of alternative paths for a quantum particle.

    DOI

    Scopus

    18
    Citation
    (Scopus)
  • ANALYSIS OF CRITICAL SHORT-TIME LANGEVIN DYNAMICS IN TWO-DIMENSIONAL phi(4) THEORY ON THE BASIS OF A HIGHER-ORDER ALGORITHM

    Tsuyoshi Otobe, Hiromichi Nakazato, Keisuke Okano, Kazuya Yuasa, Nozomu Hattori

    INTERNATIONAL JOURNAL OF MODERN PHYSICS C   20 ( 5 ) 735 - 745  2009.05  [Refereed]

     View Summary

    We investigate the critical short-time scaling of the two-dimensional lattice phi(4) field theory with a Langevin dynamics. Starting from a "hot" initial configuration but with a small magnetization, the critical initial increase of the magnetization is observed through which we determine the critical point. From the short-time relaxation dynamics of various quantities at the critical point obtained, the dynamic critical exponents theta, z and the static exponent beta/nu are evaluated. In executing a Langevin simulation, an appropriate discretization method with respect to the time degree of freedom becomes essentially important to be adopted and we show that the well-know second-order form of discretized Langevin equation works well to investigate the short-time dynamics.

    DOI

    Scopus

  • Entanglement of electrons field-emitted from a superconductor

    Kazuya Yuasa, Paolo Facchi, Rosario Fazio, Hiromichi Nakazato, Ichiro Ohba, Saverio Pascazio, Shuichi Tasaki

    PHYSICAL REVIEW B   79 ( 18 ) 180503  2009.05  [Refereed]

     View Summary

    Under appropriate circumstances the electrons emitted from a superconducting tip can be entangled. We analyze these nonlocal correlations by studying the coincidences of the field-emitted electrons and show that electrons emitted in opposite directions violate Bell's inequality. We scrutinize the interplay between the bosonic nature of Cooper pairs and the fermionic nature of electrons. We further discuss the feasibility of our analysis in the light of present experimental capabilities.

    DOI

    Scopus

    6
    Citation
    (Scopus)
  • State tomography of a chain of qubits embedded in a spin field-effect transistor via repeated spin-blockade measurements on the edge qubit

    Kazuya Yuasa, Kosuke Okano, Hiromichi Nakazato, Saori Kashiwada, Kanji Yoh

    PHYSICAL REVIEW B   79 ( 7 ) 075318  2009.02  [Refereed]

     View Summary

    As a possible physical realization of a quantum information processor, a system with stacked self-assembled InAs quantum dots buried in GaAs adjacent to the channel of a spin field-effect transistor has been proposed. In this system, only one of the stacked qubits, i.e., the edge qubit (the qubit closest to the channel), is measurable via "spin-blockade measurement." It is shown that the state tomography of the whole chain of the qubits is still possible even under such a restricted accessibility. The idea is to make use of the entangling dynamics of the qubits. A recipe for the two-qubit system is explicitly constructed and the effect of an imperfect fidelity of the measurement is clarified. A general scheme for multiple qubits based on repeated measurements is also presented.

    DOI CiNii

    Scopus

    2
    Citation
    (Scopus)
  • A Measurement-Based Purification Scheme and Decoherence

    H. Nakazato

    in PHYSICS OF SELF-ORGANIZATION SYSTEMS (Proc. of the 5th COE Symp., September 2007)     88 - 105  2008.05  [Refereed]

  • Lateral effects in fermion antibunching

    K. Yuasa, P. Facchi, H. Nakazato, I. Ohba, S. Pascazio, S. Tasaki

    PHYSICAL REVIEW A   77 ( 4 )  2008.04  [Refereed]

     View Summary

    Lateral effects are analyzed in the antibunching of a beam of free noninteracting fermions. The emission of particles from a source is dynamically described in a three-dimensional full quantum-field-theoretical framework. The size of the source and the detectors, as well as the temperature of the source are taken into account and the behavior of the visibility is scrutinized as a function of these parameters.

    DOI

    Scopus

    5
    Citation
    (Scopus)
  • Estimation of the repeatedly projected reduced density matrix under decoherence

    H. Nakazato, K. Yuasa, B. Militello, A. Messina

    PHYSICAL REVIEW A   77 ( 4 )  2008.04  [Refereed]

     View Summary

    Decoherence is believed to deteriorate the ability of a purification scheme that is based on the idea of driving a system to a pure state by repeatedly measuring another system in interaction with the former and hinder for a pure state to be extracted asymptotically. Nevertheless, we find a way out of this difficulty by deriving an analytic expression of the reduced density matrix for a two-qubit system immersed in a bath. It is shown that we can still extract a pure state if the environment brings about only dephasing effects. In addition, for a dissipative environment, there is a possibility of obtaining a dominant pure state when we perform a finite number of measurements.

    DOI

    Scopus

    5
    Citation
    (Scopus)
  • Oscillations of the purity in the repeated-measurement-based generation of quantum states

    B. Militello, K. Yuasa, H. Nakazato, A. Messina

    PHYSICAL REVIEW A   77 ( 4 )  2008.04  [Refereed]

     View Summary

    Repeated observations of a quantum system interacting with another one can drive the latter toward a particular quantum state, irrespective of its initial condition, because of an effective nonunitary evolution. If the target state is a pure one, the degree of purity of the system approaches unity, even when the initial condition of the system is a mixed state. In this paper we study the behavior of the purity from the initial value to the final one, that is, unity. Depending on the parameters, after a finite number of measurements, the purity exhibits oscillations that brings about a lower purity than that of the initial state, which is a point to be taken care of in concrete applications.

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Influence of dissipation on the extraction of quantum states via repeated measurements

    B. Militello, K. Yuasa, H. Nakazato, A. Messina

    PHYSICAL REVIEW A   76 ( 4 )  2007.10  [Refereed]

     View Summary

    A quantum system put in interaction with another one that is repeatedly measured is subject to a nonunitary dynamics, through which it is possible to extract subspaces. This key idea has been exploited to propose schemes aimed at the generation of pure quantum states (purification). All such schemes have so far been considered in the ideal situations of isolated systems. In this paper, we analyze the influence of non-negligible interactions with environment during the extraction process, with the scope of investigating the possibility of purifying the state of a system in spite of the sources of dissipation. A general framework is presented and a paradigmatic example consisting of two interacting spins immersed in a bosonic bath is studied. The effectiveness of the purification scheme is discussed in terms of purity for different values of the relevant parameters and in connection with the bath temperature.

    DOI

    Scopus

    11
    Citation
    (Scopus)
  • Diffusion and transfer of entanglement in an array of inductively coupled flux qubits

    Rosanna Migliore, Kazuya Yuasa, Marina Guccione, Hiromichi Nakazato, Antonino Messina

    PHYSICAL REVIEW B   76 ( 5 ) 052501  2007.08  [Refereed]

     View Summary

    A theoretical scheme to generate multipartite entangled states in a Josephson planar-designed architecture is reported. This scheme improves the one published by Migliore [Phys. Rev. B 74, 104503 (2006)] since it speeds up the generation of W entangled states in an MxN array of inductively coupled Josephson flux qubits by reducing the number of necessary steps. In addition, the same protocol is shown to be able to transfer the W state from one row to the other.

    DOI CiNii

    Scopus

    6
    Citation
    (Scopus)
  • On the assumption of initial factorization in the master equation for weakly coupled systems II: Solvable models

    K. Yuasa, S. Tasaki, P. Facchi, G. Kimura, H. Nakazato, I. Ohba, S. Pascazio

    ANNALS OF PHYSICS   322 ( 3 ) 657 - 676  2007.03  [Refereed]

     View Summary

    We analyze some solvable models of a quantum mechanical system in interaction with a reservoir when the initial state is not factorized. We apply Nakajima-Zwanzig's projection method by choosing a reference state of the reservoir endowed with the mixing property. In van Hove's limit, the dynamics is described in terms of a master equation. We observe that Markovianity becomes a valid approximation for timescales that depend both on the form factors of the interaction and on the observables of the reservoir that can be measured. (c) 2006 Elsevier Inc. All rights reserved.

    DOI

    Scopus

    14
    Citation
    (Scopus)
  • On the assumption of initial factorization in the master equation for weakly coupled systems I: General framework

    S. Tasaki, K. Yuasa, P. Facchi, G. Kimura, H. Nakazato, I. Ohba, S. Pascazio

    ANNALS OF PHYSICS   322 ( 3 ) 631 - 656  2007.03  [Refereed]

     View Summary

    We analyze the dynamics of a quantum mechanical system in interaction with a reservoir when the initial state is not factorized. In the weak-coupling (van Hove) limit, the dynamics can be properly described in terms of a master equation, but a consistent application of Nakajima-Zwanzig's projection method requires that the reference (not necessarily equilibrium) state of the reservoir be endowed with the mixing property. (c) 2006 Elsevier Inc. All rights reserved.

    DOI

    Scopus

    17
    Citation
    (Scopus)
  • State tomography of layered qubits via spin blockade measurements on the edge qubit in a spin field-effect transistor structure embedded with quantum dots

    K. Yuasa, K. Okano, H. Nakazato, S. Kashiwada, K. Yoh

    PHYSICS OF SEMICONDUCTORS, PTS A AND B   893   1109 - +  2007  [Refereed]

     View Summary

    As a promising physical realization of a quantum computer, we discuss a system with stacked quantum dots buried in adjacent to the channel of a spin field-effect transistor. In this scheme, one can measure only the edge qubit (nearest to the channel) via the spin-blockade measurement, but still it is possible to know the state of the whole qubits.

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Resonant scattering can enhance the degree of entanglement

    Kazuya Yuasa, Hiromichi Nakazato

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   40 ( 2 ) 297 - 308  2007.01  [Refereed]

     View Summary

    Generation of entanglement between two qubits by scattering an entanglement mediator is discussed. The mediator bounces between the two qubits and exhibits a resonant scattering. It is clarified how the degree of the entanglement is enhanced by the constructive interference of such bouncing processes. Maximally entangled states are available via adjusting the incident momentum of the mediator or the distance between the two qubits, but their fine tunings are not necessarily required to gain highly entangled states and a robust generation of entanglement is possible.

    DOI

    Scopus

    41
    Citation
    (Scopus)
  • Solution of the Lindblad equation in the Kraus representation

    H. Nakazato, Y. Hida, K. Yuasa, B. Militello, A. Napoli, A. Messina

    PHYSICAL REVIEW A   74 ( 6 )  2006.12  [Refereed]

     View Summary

    The so-called Lindblad equation, a typical master equation describing the dissipative quantum dynamics, is shown to be solvable for finite-level systems in a compact form without resort to writing it down as a set of equations among matrix elements. The solution is then naturally given in an operator form, known as the Kraus representation. Following a few simple examples, the general applicability of the method is clarified.

    DOI

    Scopus

    32
    Citation
    (Scopus)
  • Generation of multipartite entangled states in Josephson architectures

    Rosanna Migliore, Kazuya Yuasa, Hiromichi Nakazato, Antonino Messina

    PHYSICAL REVIEW B   74 ( 10 )  2006.09  [Refereed]

     View Summary

    We propose and analyze a scheme for the generation of multipartite entangled states in a system of inductively coupled Josephson flux qubits. The qubits have fixed eigenfrequencies during the whole process in order to minimize decoherence effects and their inductive coupling can be turned on and off at will by tuning an external control flux. Within this framework, we will show that a W state in a system of three or more qubits can be generated by exploiting the sequential one by one coupling of the qubits with one of them playing the role of an entanglement mediator.

    DOI

    Scopus

    26
    Citation
    (Scopus)
  • Control of decoherence via quantum zeno subspaces

    P Facchi, H Nakazato, S Pascazio, S Tasaki

    INTERNATIONAL JOURNAL OF MODERN PHYSICS B   20 ( 11-13 ) 1408 - 1420  2006.05  [Refereed]

     View Summary

    We discuss three control strategies, whose objective is to counter the effects of decoherence: the first strategy hinges upon the quantum Zeno effect, the second makes use of frequent unitary interruptions ("bang-bang" pulses), and the third of a strong, continuous coupling. Decoherence can be suppressed only if the frequency tau(-1) of the measurements/pulses is large enough or if the coupling K is sufficiently strong. Otherwise, if tau(-1) or K are large, but not sufficiently large, all these control procedures accelerate decoherence.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Preparation of quantum state through Zeno-like measurements

    Kazuya Yuasa, Hiromichi Nakazato

    Journal of Physics: Conference Series   31 ( 1 ) 183 - 184  2006.03

     View Summary

    We present a novel method for preparing pure quantum states, i.e., purification through Zeno-like measurements, and its possible applications and extensions. © 2006 IOP Publishing Ltd.

    DOI

    Scopus

  • A Purification Scheme and Entanglement Distillations

    H. Nakazato, M. Unoki, K. Yuasa

    Quantum Information and Computing (World Sci. Pub., Singapore)     259 - 273  2006.03  [Refereed]

  • Projection Operator Method for Open Quantum Systems Revisited(Fundamental Problems and Applications of Quantum Field Theory)

    Yuasa K., Tasaki S., Facchi P., Kimura G., Nakazato H., Ohba I., Pascazio S.

    Soryushiron Kenkyu Electronics   113 ( 1 ) A15  2006

    DOI CiNii

  • Short-Time Scaling in a Critical Relaxation Dynamics with a Kernelized Langevin Equation(Fundamental Problems and Applications of Quantum Field Theory)

    Hattori Nozomu, Otobe Tsuyoshi, Yuasa Kazuya, Nakazato Hiromichi, Okano Keisuke

    Soryushiron Kenkyu Electronics   113 ( 1 ) A58  2006

    DOI CiNii

  • Generation of multipartite entangled states in Josephson architectures

    Rosanna Migliore, Kazuya Yuasa, Hiromichi Nakazato, Antonino Messina

    Physical Review B - Condensed Matter and Materials Physics   74 ( 10 ) 104503  2006  [Refereed]

     View Summary

    We propose and analyze a scheme for the generation of multipartite entangled states in a system of inductively coupled Josephson flux qubits. The qubits have fixed eigenfrequencies during the whole process in order to minimize decoherence effects and their inductive coupling can be turned on and off at will by tuning an external control flux. Within this framework, we will show that a W state in a system of three or more qubits can be generated by exploiting the sequential one by one coupling of the qubits with one of them playing the role of an entanglement mediator. © 2006 The American Physical Society.

    DOI

    Scopus

    26
    Citation
    (Scopus)
  • Quantum entanglement formation by repeated spin blockade measurements in a spin field-effect transistor structure embedded with quantum dots

    K Yoh, K Yuasa, H Nakazato

    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES   29 ( 3-4 ) 674 - 678  2005.11  [Refereed]

     View Summary

    We propose a method of operating a quantum state machine made of stacked quantum dots buried in adjacent to the channel of a spin field-effect transistor (FET) [S. Datta, B. Das, Appl. Phys. Lett. 56 (1990) 665; K. Yoh, et al., Proceedings of the 23rd International Conference oil Physics of Semiconductors (ICPS) 2004; H. Ohno, K. Yoh et al., Jpn. J. Appl. Phys. 42 (2003) L87; K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134]. In this method, a spin blockade measurement extracts the quantum state of a nearest quantum dot through Coulomb blockade [K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134; K. Yoh, H. Kazama, Physica E 7 (2000) 440] of the adjacent channel conductance. Repeated quantum Zeno-like (QZ) measurements [H. Nakazato, et al., Phys. Rev. Lett. 90 (2003) 060401] of the spin blockade is shown to purify the quantum dot states within several repetitions. The growth constraints of the stacked InAs quantum dots are shown to provide an exchange interaction energy in the range of 0.01-1 meV [S. Itoh, et al., Jpn. J. Appl. Phys. 38 (1999) L917; A. Tackeuchi, et al., Jpn. J. Appl. Phys. 42 (2003) 4278]. We have verified that one can reach the fidelity of 90% by repeating the measurement twice, and that of 99.9% by repeating only eleven QZ measurements. Entangled states with two and three vertically stacked dots are achieved with the sampling frequency of the order of 100 MHz. (c) 2005 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    8
    Citation
    (Scopus)
  • A simple scheme to entangle distant qubits from a mixed state via an entanglement mediator

    K Yuasa, H Nakazato

    PROGRESS OF THEORETICAL PHYSICS   114 ( 3 ) 523 - 531  2005.09  [Refereed]

     View Summary

    A simple scheme to prepare an entanglement between two separated qubits from a given mixed state is proposed. A single qubit (entanglement mediator) is repeatedly made to interact locally and consecutively with the two qubits through rotating-wave couplings and is then measured. It is shown that we need to repeat this kind of process only three times to establish a maximally entangled state directly from an arbitrary initial mixed state, with no need to prepare the state of the qubits in advance or to rearrange the setup step by step. Furthermore, the maximum yield realizable with this scheme is compatible with the maximum entanglement, provided that the coupling constants are properly tuned.

    DOI CiNii

    Scopus

    12
    Citation
    (Scopus)
  • Governing survival probability to distill quantum states

    B Militello, A Messina, H Nakazato

    OPTICS AND SPECTROSCOPY   99 ( 3 ) 438 - 442  2005.09  [Refereed]

     View Summary

    A quantum system interacting with a repeatedly measured one undergoes a nonunitary time evolution pushing it into some specific subspaces. We deeply investigate the origin of the relevant selection rule, bringing to the light its connection with the survival probability related with the two-system interaction. The possibility of inducing an effective dynamics in the distilled subspace just during the distillation process is demonstrated. (c) 2005 Pleiades Publishing, Inc.

    DOI CiNii

    Scopus

    3
    Citation
    (Scopus)
  • Steering distillation processes through quantum Zeno dynamics

    B Militello, H Nakazato, A Messina

    PHYSICAL REVIEW A   71 ( 3 )  2005.03  [Refereed]

     View Summary

    A quantum system in interaction with a repeatedly measured one undergoes a nonunitary time evolution and is pushed into a subspace substantially determined by the two-system coupling. The possibility of suitably modifying such an evolution through quantum Zeno dynamics (i.e., the generalized quantum Zeno effect) addressing the system toward an a priori decided target subspace is illustrated. Applications and their possible realizations in the context of trapped ions are also discussed.

    DOI

    Scopus

    9
    Citation
    (Scopus)
  • Control of decoherence: Analysis and comparison of three different strategies

    P Facchi, S Tasaki, S Pascazio, H Nakazato, A Tokuse, DA Lidar

    PHYSICAL REVIEW A   71 ( 2 )  2005.02  [Refereed]

     View Summary

    We analyze and compare three different strategies, all aimed at controlling and eventually halting decoherence. The first strategy hinges upon the quantum Zeno effect, the second makes use of frequent unitary interruptions ("bang-bang" pulses and their generalization, quantum dynamical decoupling), and the third uses a strong, continuous coupling. Decoherence is shown to be suppressed only if the frequency N of the measurements or pulses is large enough or if the coupling K is sufficiently strong. Otherwise, if N or K is large, but not extremely large, all these control procedures accelerate decoherence. We investigate the problem in a general setting and then consider some practical examples, relevant for quantum computation.

    DOI

    Scopus

    191
    Citation
    (Scopus)
  • Governing survival probability to distill quantum states

    Militello, B., Messina, A., Nakazato, H.

    Optika i Spektroskopiya   99 ( 3 )  2005

  • Distillation of entanglement between distant systems by repeated measurements on an entanglement mediator

    G Compagno, A Messina, H Nakazato, A Napoli, M Unoki, K Yuasa

    PHYSICAL REVIEW A   70 ( 5 ) 1 - 52316  2004.11  [Refereed]

     View Summary

    A recently proposed purification method, in which Zeno-like measurements of a subsystem can bring about a distillation of another subsystem in interaction with the former, is utilized to yield entangled states between distant systems. It is shown that measurements of a two-level system, locally interacting with two other spatially separated uncoupled subsystems, can distill entangled states from the latter irrespective of the initial states of the two subsystems.

    DOI J-GLOBAL

    Scopus

    26
    Citation
    (Scopus)
  • Entanglement purification through Zeno-like measurements

    K Yuasa, H Nakazato, M Unoki

    JOURNAL OF MODERN OPTICS   51 ( 6-7 ) 1005 - 1009  2004.04  [Refereed]

     View Summary

    We present a novel method for purifying quantum states, i.e. purification through Zeno-like measurements, and show an application to entanglement purification.

    DOI

  • Preparation and entanglement purification of qubits through Zeno-like measurements

    Hiromichi Nakazato, Makoto Unoki, Kazuya Yuasa

    Physical Review A - Atomic, Molecular, and Optical Physics   70 ( 1 ) 1 - 12303  2004  [Refereed]

     View Summary

    A mechanism to purify quantum states by Zeno-like measurements was discussed and was applied to simple qubit systems. A pure state was extracted in a quantum system by a series of measurements on another quantum system in interaction with the former. Entanglement purification was one of the application in the purification method. An extension of this method was in the entanglement between two spatially separated qubits which was necessary for quantum communication and quantum teleportation.

    DOI J-GLOBAL

    Scopus

    56
    Citation
    (Scopus)
  • Purification of Quantum State through Zeno-like Measurements

    Kazuya Yuasa, Hiromichi Nakazato, Tomoko Takazawa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72   34 - 37  2003.11  [Refereed]

     View Summary

    We present a novel procedure to purify quantum states, i.e., purification through Zeno-like measurements. By simply repeating one and the same measurement on a quantum system, one can purify another system in interaction with the former. The conditions for the (efficient) purification are specified on a rather general setting, and the framework of the method possesses wide applicability. It is explicitly demonstrated on a specific setup that the purification becomes very efficient by tuning relevant parameters.

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • Optimization of a neutron-spin test of the quantum Zeno effect

    P Facchi, Y Nakaguro, H Nakazato, S Pascazio, M Unoki, K Yuasa

    PHYSICAL REVIEW A   68 ( 1 ) 1 - 12107  2003.07  [Refereed]

     View Summary

    A neutron-spin experimental test of the quantum Zeno effect (QZE) is discussed from a practical point of view, where the nonideal efficiency of the magnetic mirrors, used for filtering the spin state, is taken into account. In the idealized case, the number N of (ideal) mirrors can be indefinitely increased, yielding an increasingly better QZE. In contrast, in a practical situation with imperfect mirrors, there is an optimal number of mirrors, N-opt, at which the QZE becomes maximum: more frequent measurements would deteriorate the performance. However, a quantitative analysis shows that a good experimental test of the QZE is still feasible. These conclusions are of general validity: in a realistic experiment, the presence of losses and imperfections leads to an optimal frequency N-opt, which is in general finite. One should not increase N beyond N-opt. A convenient formula for N-opt, valid in a broad framework, is derived as a function of the parameters characterizing the experimental setup.

    DOI J-GLOBAL

    Scopus

    2
    Citation
    (Scopus)
  • Purification through Zeno-like measurements

    H Nakazato, T Takazawa, K Yuasa

    PHYSICAL REVIEW LETTERS   90 ( 6 ) 060401  2003.02  [Refereed]

     View Summary

    A series of frequent measurements on a quantum system (Zeno-like measurements) is shown to result in the "purification" of another quantum system in interaction with the former. Even though the measurements are performed on the former system, their effect drives the latter into a pure state, irrespectively of its initial (mixed) state, provided certain conditions are satisfied.

    DOI PubMed

    Scopus

    19
    Citation
    (Scopus)
  • Journal of the Physical Society of Japan: Preface

    Ohba, I., Aizawa, Y., Daishido, T., Kurihara, S., Maeda, K., Nakazato, H., Tasaki, S., Yuasa K.

    Journal of the Physical Society of Japan   72 ( SUPPL.C )  2003

  • Proceedings of Waseda International Symposium on Fundamental Physics ---New Perspectives in Quantum Physics---

    I. Ohba, Y. Aizawa, T. Daishido, S. Kurihara, K.-I. Maeda, H. Nakazato, S. Tasaki, K. Yuasa

    The Physical Society of Japan    2003

  • Purification and entanglement distillations

    H. Nakazato

    ICQI03TU, Tokyo, Japan    2003

  • A purification scheme and entanglement distillation

    H. Nakazato

    ICQI03WU, Tokyo, Japan    2003

  • Proceedings of Waseda International Symposium on Fundamental Physics ---New Perspectives in Quantum Physics---

    I. Ohba, Y. Aizawa, T. Daishido, S. Kurihara, K.-I. Maeda, H. Nakazato, S. Tasaki, K. Yuasa

    The Physical Society of Japan    2003

  • Purification and entanglement distillations

    H. Nakazato

    ICQI03TU, Tokyo, Japan    2003

  • A purification scheme and entanglement distillation

    H. Nakazato

    ICQI03WU, Tokyo, Japan    2003

  • To decay or not to decay? Temporal behavior of a quantum system - Analysis based on a solvable model

    H Nakazato

    FUNDAMENTAL ASPECTS OF QUANTUM PHYSICS   17   267 - 283  2003  [Refereed]

     View Summary

    The exact expression of the survival amplitude of a model system, which may describe photodetachment of a negative ion, is derived and analyzed in detail with an attention on its behavior as a function of time. The latter is governed by the location of poles of the amplitude in the complex energy plane. Poles located on the real energy axis can prevent the system from decay (known as plasmon poles), while other poles on the second Riemannian sheet give rise to exponentially decaying terms. The solvability of the model enables us to see explicitly the analytic structure of the amplitude, e.g., the movement of the poles in the complex energy plane as functions of parameters of the model. The behavior both at short and long times is also derived exactly and its peculiarity is pointed out and discussed.

    DOI

  • From the quantum zeno to the inverse quantum zeno effect

    P Facchi, H Nakazato, S Pascazio

    PHYSICAL REVIEW LETTERS   86 ( 13 ) 2699 - 2703  2001.03  [Refereed]

     View Summary

    The temporal evolution of an unstable quantum mechanical system undergoing repeated measurements is investigated. In general, by changing the time interval between successive measurements, the decay can be accelerated (inverse quantum Zeno effect) or slowed down (quantum Zeno effect), depending on the features of the interaction Hamiltonian. A geometric criterion is proposed for a transition to occur between these two regimes.

    DOI PubMed CiNii J-GLOBAL

    Scopus

    299
    Citation
    (Scopus)
  • To decay or not to decay? Temporal behavior of a quantum system

    H. Nakazato

    Japan-Italy Joint Forum Waseda Symposium    2001

  • Stability and instability in parametric resonance and quantum Zeno effect

    P Facchi, H Nakazato, S Pascazio, J Perina, J Rehacek

    PHYSICS LETTERS A   279 ( 3-4 ) 117 - 122  2001.01  [Refereed]

     View Summary

    A quantum mechanical version of a classical inverted pendulum is analyzed. The stabilization of the classical motion is reflected in the bounded evolution of the quantum mechanical operators in the Heisenberg picture. Interesting links with the quantum Zeno effect are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI CiNii J-GLOBAL

    Scopus

    10
    Citation
    (Scopus)
  • Two-level system with a noisy Hamiltonian

    H Nakazato, S Pascazio

    JOURNAL OF SUPERCONDUCTIVITY   12 ( 6 ) 843 - 849  1999.12  [Refereed]

     View Summary

    We study the dynamical properties of a two-level system in interaction with its environment, whose action on the system is modeled by means of a noise term in the Hamiltonian. We solve the Schrodinger equation, obtain an evolution equation of the Lindblad type for the noise average of the density matrix, and: discuss the results in terms of a "decoherence parameter." Finally, we concentrate our attention on the possibility of hindering the transitions between the two levels in two (apparently unrelated) ways: (a) by increasing the strength of the noise; (b) by a series of frequent measurements. There is an interesting relation between these two situations.

    DOI J-GLOBAL

    Scopus

    10
    Citation
    (Scopus)
  • Reflection and transmission in a neutron-spin test of the quantum Zeno effect

    K Machida, H Nakazato, S Pascazio, H Rauch, S Yu

    PHYSICAL REVIEW A   60 ( 5 ) 3448 - 3460  1999.11  [Refereed]

     View Summary

    The dynamics of a quantum system undergoing frequent "measurements," leading to the so-called quantum Zeno effect, is examined on the basis of a neutron-spin experiment recently proposed for its demonstration. Unlike in all previous studies, the spatial degrees of freedom of the neutron are duly taken into account. Their inclusion in the analysis is important for two reasons: first, neutron-reflection effects are shown to be very important; second, the evolution may rum out to be totally different from the ideal case. Our results can be interpreted in terms of a rigorous theorem due to Misra and Sudarshan: indeed we clarify that, in contrast with a widespread belief, a quantum Zeno effect does not halt the evolution of a quantum system; it rather modifies it, by forcing the system to remain in a certain subspace, defined by the very measurement performed. [S1050-2947(99)00811-2].

    DOI J-GLOBAL

    Scopus

    22
    Citation
    (Scopus)
  • Stochastic quantization of bottomless systems - Stationary quantities in a diffusive process

    K Yuasa, H Nakazato

    PROGRESS OF THEORETICAL PHYSICS   102 ( 4 ) 719 - 727  1999.10  [Refereed]

     View Summary

    By making use of the Langevin equation with a kernel, it was shown that the Feynman measure e(-S) can be realized in a restricted sense in a diffusive stochastic process, which diverges and has no equilibrium, for bottomless systems. In this paper, the dependence on the initial conditions and the temporal behavior are analyzed for 0-dim bottomless systems. Furthermore, it is shown that it is possible to find stationary quantities.

    DOI J-GLOBAL

    Scopus

    2
    Citation
    (Scopus)
  • Infinitely frequent measurements and quantum Zeno effect

    Z Hradil, H Nakazato, M Namiki, S Pascazio, H Rauch

    PHYSICS LETTERS A   239 ( 6 ) 333 - 338  1998.03  [Refereed]

     View Summary

    The limit of infinitely many measurements is critically analyzed within the quantum mechanical framework, in connection with the quantum Zeno effect. It is shown that such a limit is unphysical and that quantum losses are unavoidable. A specific example involving neutron spin is considered. (C) 1998 Elsevier Science B.V.

    DOI CiNii J-GLOBAL

    Scopus

    22
    Citation
    (Scopus)
  • Time development of a wave packet in potential scattering

    H Nakazato

    SYMMETRIES IN SCIENCE X   pp. 305-314   305 - 314  1998  [Refereed]

     View Summary

    A one-dimensional scattering problem off a delta-shaped potential is solved analytically and the time development of a wave packet is derived from the time-dependent Schrodinger equation. The exact and explicit expression of the scattered wave packet supplies us with interesting information about the "time delay" by potential scattering in the asymptotic region. It is demonstrated that a wave packet scattered by a spin-flipping potential can give us quite a different value for the delay times from that obtained without spin-degrees of freedom.

  • Time symmetry and quantum dephasing

    M Namiki, H Nakazato, S Pascazio

    SYMMETRIES IN SCIENCE X   pp. 315-323   315 - 323  1998  [Refereed]

     View Summary

    We first stress that the time symmetry in quantum mechanics manifests itself in the analytical properties of the Fourier transform of the evolution operator in the complex E-plane (E being the variable conjugate to time), in such a way that all singularities are distributed only on the real axis in the first Riemannian sheet, and new poles appear, in the N infinite limit (N standing for the number of degrees of freedom of detector or instrument concerned), on the second Riemannian sheet in a symmetric way with respect to the real axis. We then examine the symmetry-breaking phenomenon, such as decay or dissipation, by setting up the initial value problem: The temporal evolution of the transition probability is divided into three parts, the first being Gaussian for very short times, the second exponential for intermediate times and the third of the power type for very long times. We know that the Gaussian decay is directly connected to the so-called quantum Zeno effect, the exponential decay corresponds to a sort of dephasing process, because the time rate of the total transition probability becomes a sum of time rates of partial probabilities, and both the Gaussian-like and power-like decay will disappear, leaving only the exponential one, in the van Hove limit. The dominance of the exponential decay is equivalent to the appearance of a master equation, which tells us that we have no phase-correlation but decoherence or dephasing. All temporal behaviors of quantum-mechanical transition probability and related physics are reflected in the analytical property of the Fourier transform of the evolution operator.

  • Temporal behavior of quantum systems and quantum zeno effect

    S Pascazio, H Nakazato, M Namiki

    SYMMETRIES IN SCIENCE X   pp. 337-344   337 - 344  1998  [Refereed]

     View Summary

    The temporal behavior of an unstable system is analyzed quantum mechanically and compared to the exponential decay law. The general mathematical features of the quantum evolution, yielding a quadratic region at short times and a power law at long times, are briefly reviewed.
    The consequences of the short-time quadratic evolution are curious: By performing many measurements in rapid succession on a quantum system, in order to check whether it is still in its initial state, one can hinder its evolution. This phenomenon is known as the quantum Zeno effect and is discussed in detail. In this respect, a specific example involving neutron spin is considered. Finally, we focus our attention on some interesting features of the evolution law.

  • Time development of a wave packet and the time delay

    H Nakazato

    FOUNDATIONS OF PHYSICS   27 ( 12 ) 1709 - 1723  1997.12  [Refereed]

     View Summary

    A one-dimensional scattering problem off a delta-shaped potential is solved analytically and the time development of a wave packet is derived from the time-dependent Schrodinger equation. The exact and explicit expression of the scattered wave packet supplies us with interesting information about the 'time delay' by potential scattering in the asymptotic region. It is demonstrated that a wave packet scattered by a spin-flipping potential can give us quite a different value for the delay times from that obtained without spin-degrees of freedom.

    DOI J-GLOBAL

    Scopus

    5
    Citation
    (Scopus)
  • Emergence of a Wiener process as a result of the quantum mechanical interaction with a macroscopic medium

    R Blasi, H Nakazato, M Namiki, S Pascazio

    PHYSICA A   245 ( 1-2 ) 189 - 211  1997.10  [Refereed]

     View Summary

    We analyze a modified version of the Coleman-Hepp model, which is able to take into account energy-exchange processes between the incoming particle and the linear array made up of N spin-1/2 systems. We bring to light the presence of a Wiener dissipative process in the weak-coupling, macroscopic (N --> infinity) limit. In such a limit and a restricted portion of the total Hilbert space, the particle undergoes a sort of Brownian motion, while the flee Hamiltonian of the spin array serves as a Wiener process. No partial trace is computed over the states of the spin system (which plays the role of ''reservoir''). The mechanism of appearance of the stochastic process is discussed and contrasted to other noteworthy examples in the literature. The links with van Hove's ''lambda(2)T'' limits are emphasized.

    DOI J-GLOBAL

  • A solvable model for quantum mechanical dissipation

    H Nakazato, S Pascazio

    NEW PERSPECTIVES IN THE PHYSICS OF MESOSCOPIC SYSTEMS   pp. 216-224   216 - 224  1997  [Refereed]

     View Summary

    We study the Coleman-Hepp or AgBr Hamiltonian, concentrating our attention on a weak-coupling, macroscopic Limit that yields dissipative effects. We analyze the role played by Van Hove's "lambda(2)T" limit.

  • Dissipative behavior of a quantum system interacting with a macroscopic medium

    R Blasi, H Nakazato, M Namiki, S Pascazio

    PHYSICS LETTERS A   223 ( 5 ) 320 - 326  1996.12  [Refereed]

     View Summary

    The modified Coleman-Hepp (AgBr) model describes the interaction between an ultrarelativistic quantum mechanical particle Q and an N-spin array D (a macroscopic medium in the N --> infinity limit). We prove that the energy operator for D essentially behaves as a Wiener process in the weak-coupling, macroscopic limit, in a restricted state space. No assumptions are made on the spectrum of the Hamiltonian of the macroscopic system D. The mechanism of appearance of such a stochastic process and its relevance to issues like dissipation and irreversibility are briefly discussed.

    DOI CiNii J-GLOBAL

    Scopus

    3
    Citation
    (Scopus)
  • Quantum dephasing by chaos

    H Nakazato, M Namiki, S Pascazio, Y Yamanaka

    PHYSICS LETTERS A   222 ( 3 ) 130 - 136  1996.10  [Refereed]

     View Summary

    We examine whether the chaotic behavior of classical systems with a limited number of degrees of freedom can produce quantum dephasing, against the conventional idea that dephasing takes place only in large systems with a huge number of constituents and complicated internal interactions. On the basis of this analysis, we briefly discuss the possibility of defining quantum chaos and of inventing a ''chaos detector''.

    DOI CiNii J-GLOBAL

    Scopus

    5
    Citation
    (Scopus)
  • Understanding the quantum Zeno effect

    H Nakazato, M Namiki, S Pascazio, H Rauch

    PHYSICS LETTERS A   217 ( 4-5 ) 203 - 208  1996.07  [Refereed]

     View Summary

    The quantum Zeno effect consists in the hindrance of the evolution of a quantum system that is very frequently monitored and found to be in its initial state at every single measurement. On the basis of the correct formula for the survival probability, i.e. the probability of finding the system in its initial state at every single measurement, we critically analyze a recent proposal and experimental test that make use of an oscillating system.

    DOI CiNii J-GLOBAL

    Scopus

    56
    Citation
    (Scopus)
  • Effect of fluctuation and dissipation on neutron scattering

    K. Machida, H. Nakazato, M. Namiki, S. Pascazio

    J. Phys. Soc. Jpn. Suppl.A   65  1996

  • Quantum Zeno effect

    S. Pascazio, H. Nakazato, M. Namiki

    J. Phys. Soc. Jpn. Suppl.A   65  1996

  • Effect of fluctuation and dissipation on neutron scattering

    International Symposium on Advances in Neutron Optics and Related Research Facilities    1996

  • Effect of fluctuation and dissipation on neutron scattering

    K. Machida, H. Nakazato, M. Namiki, S. Pascazio

    J. Phys. Soc. Jpn. Suppl.A   65  1996

  • Quantum Zeno Effect

    International Symposium on Advances in Neutron Optics and Related Research Facilities    1996

  • Temporal behavior of quantum mechanical systems

    H Nakazato, M Namiki, S Pascazio

    INTERNATIONAL JOURNAL OF MODERN PHYSICS B   10 ( 3 ) 247 - 295  1996.01  [Refereed]

     View Summary

    The temporal behavior of quantum mechanical systems is reviewed. We mainly focus our attention on the time development of the so-called ''survival'' probability of those systems that are initially prepared in eigenstates of the unperturbed Hamiltonian, by assuming that the latter has a continuous spectrum.
    The exponential decay of the survival probability, familiar, for example, in radioactive decay phenomena, is representative of a purely probabilistic character of the system under consideration and is naturally expected to lead to a master equation. This behavior, however, can be found only at intermediate times, for deviations from it exist both at short and long times and can have significant consequences.
    After a short introduction to the long history of the research on the temporal behavior of such quantum mechanical systems, the short-time behavior and its controversial consequences when it is combined with von Neumann's projection postulate in quantum measurement theory are critically overviewed from a dynamical point of view. We also discuss the so-called quantum Zeno effect from this standpoint.
    The behavior of the survival amplitude is then scrutinized by investigating the analytic properties of its Fourier and Laplace transforms. The analytic property that there is no singularity except a branch cut running along the real energy axis in the first Riemannian sheet is an important reflection of the time-reversal invariance of the dynamics governing the whole process. It is shown that the exponential behavior is due to the presence of a simple pole in the second Riemannian sheet, while the contribution of the branch point yields a power behavior for the amplitude. The exponential decay form is cancelled at short times and dominated at very long times by the branch-point contributions, which give a Gaussian behavior for the former and a power behavior for the latter.
    In order to realize the exponential law in quantum theory, it is essential to take into account a certain kind of macroscopic nature of the total system, since the exponential behavior is regarded as a manifestation of a complete loss of coherence of the quantum subsystem under consideration. In this respect, a few attempts at extracting the exponential decay form on the basis of quantum theory, aiming at the master equation, are briefly reviewed, including van Hove's pioneering work and his well-known ''lambda(2)T'' limit.
    In the attempt to further clarify the mechanism of the appearance of a purely probabilistic behavior without resort to any approximation, a solvable dynamical model is presented and extensively studied. The model describes an ultrarelativistic particle interacting with N two-level systems (called ''spins'') and is shown to exhibit an exponential behavior at all times in the weak-coupling, macroscopic limit. Furthermore, it is shown that the model can even reproduce the short-time Gaussian behavior followed by the exponential law when an appropriate initial state is chosen. The analysis is exact and no approximation is involved. An interpretation for the change of the temporal behavior in quantum systems is drawn from the results obtained. Some implications for the quantum measurement problem are also discussed, in particular in connection with dissipation.

    DOI J-GLOBAL

    Scopus

    202
    Citation
    (Scopus)
  • On the short-time behavior of quantum mechanical systems

    H Nakazato, S Pascazio

    MODERN PHYSICS LETTERS A   10 ( 40 ) 3103 - 3111  1995.12  [Refereed]

     View Summary

    The conditions that yield deviations from a purely exponential behavior of a quantum mechanical system at short times are analyzed with special emphasis on the boundedness of the Hamiltonian. A few practical examples are considered. The problem of dissipation in quantum mechanics and quantum field theory is also briefly discussed.

    DOI J-GLOBAL

  • ON THE QUANTUM ZENO EFFECT

    H NAKAZATO, M NAMIKI, S PASCAZIO, H RAUCH

    PHYSICS LETTERS A   199 ( 1-2 ) 27 - 32  1995.03  [Refereed]

     View Summary

    The limit of infinitely frequent measurements (continuous observation), yielding the quantum Zeno paradox, is critically analyzed and shown to be unphysical. A specific example involving neutron spin is considered and some practical estimates are given.

    DOI

    Scopus

    52
    Citation
    (Scopus)
  • A COHERENT UNDERSTANDING OF SOLVABLE MODELS FOR QUANTUM MEASUREMENT PROCESSES

    H NAKAZATO, S PASCAZIO

    PHYSICS LETTERS A   192 ( 2-4 ) 169 - 174  1994.09  [Refereed]

     View Summary

    By making use of Schwinger's oscillator model of angular momentum, we put forward an interesting connection among three solvable Hamiltonians, widely used for discussions on the quantum measurement problem. This connection implies that a particular macroscopic limit has to be taken for these models to be physically sensible.

  • EXPONENTIAL BEHAVIOR OF A QUANTUM SYSTEM IN A MACROSCOPIC MEDIUM

    H NAKAZATO, M NAMIKI, S PASCAZIO

    PHYSICAL REVIEW LETTERS   73 ( 8 ) 1063 - 1066  1994.08  [Refereed]

     View Summary

    An exponential behavior at all times is derived for a solvable dynamical model in the weak-coupling macroscopic limit. Some implications for the quantum measurement problems are discussed, in particular in connection with dissipation.

  • 2
    Citation
    (Scopus)
  • MACROSCOPIC LIMIT OF A SOLVABLE DYNAMICAL MODEL

    H NAKAZATO, S PASCAZIO

    PHYSICAL REVIEW A   48 ( 2 ) 1066 - 1081  1993.08  [Refereed]

     View Summary

    The interaction between an ultrarelativistic particle and a linear array made up of N two-level systems (AgBr molecules) is studied by making use of a modified version of the Coleman-Hepp Hamiltonian. Energy-exchange processes between the particle and the molecules axe properly taken into account, and the evolution of the total system is calculated exactly both when the array is initially in the ground state and in a thermal state. In the weak-coupling, macroscopic (N --> infinity) limit, the system remains solvable and leads to interesting connections with the Jaynes-Cummings model, which describes the interaction of a particle with a maser. The visibility of the interference pattern produced by the two branch waves of the particle is computed, and the conditions under which the spin array behaves as a ''detector'' are investigated. The behavior of the visibility yields good insights into the issue of quantum measurements: It is found that, in the N --> infinity limit, a superselection-rule space appears in the description of the (macroscopic) apparatus. In general, an initial thermal state of the ''detector'' provokes a more substantial loss of quantum coherence than an initial ground state. It is argued that a system increasingly loses coherence as the temperature of the detector increases. The problem of ''imperfect measurements'' is also briefly discussed.

  • 1
    Citation
    (Scopus)
  • Spectrum of the Fokker-Planck Hamiltonian in Minkowski Space :

    NAKAZATO Hiromichi

    Progress of theoretical physics. Supplement   ( 111 ) 349 - 371  1993

     View Summary

    The stochastic quantization method is formulated in Minkowski space. Owing to a complex drift which appears in the Langevin equation (one of the basic equations of this quantization method), it is not manifest whether the system has a definite equilibrium state. To guarantee the system will reach equilibrium, the so-called ie-prescription is adopted. It is shown that in the Fokker-Planck formalism there naturally appears an effective Fokker-Planck distribution, which is complex-valued and is to be expected to become the Feynman amplitude e^<iS> in the equilibrium limit. The dynamics which governs the hypothetical thermal process can be clarified by investigating the spectrum of the Fokker-Planck Hamiltonian. Here the spectrum is studied by means of the δ-expansion technique of Bender et al. and the ordinary perturbation theory to show its important role.

    DOI CiNii

  • SOLVABLE DYNAMIC-MODEL FOR A QUANTUM MEASUREMENT PROCESS

    H NAKAZATO, S PASCAZIO

    PHYSICAL REVIEW LETTERS   70 ( 1 ) 1 - 4  1993.01  [Refereed]

     View Summary

    A model Hamiltonian describing an energy-exchange process between an ultrarelativistic particle and a one-dimensional spin array is proposed and solved exactly. Interesting relations with the quantum measurement problem are discussed.

  • LOSS OF QUANTUM-MECHANICAL COHERENCE IN A MEASUREMENT PROCESS

    H NAKAZATO, S PASCAZIO

    PHYSICAL REVIEW A   45 ( 7 ) 4355 - 4366  1992.04  [Refereed]

     View Summary

    A quantum-mechanical measurement process is analyzed in terms of a model Hamiltonian describing the interaction between a quantum system (a "particle") and a macroscopic apparatus (a "detector"), which is assumed to be made up of N two-level elementary constituents ("molecules"). The description of the molecule locations introduces an effective fluctuating coupling constant, and this provokes a loss of quantum-mechanical coherence in the limit of large N. It is argued that coherence is lost statistically, as a result of the interaction: The collapse of the wave function is indeed obtained when the same experiment is performed many times, as a result of the microscopic differences among macroscopically identical initial states of the detector. In this way, insight is obtained into the mechanism engendering the loss of coherence suffered by a quantum-mechanical system when interacting with a macroscopic apparatus, and the concept of "wave-function collapse" is replaced by that of a statistically defined dephasing process. No classical behavior of the detection system is postulated and the presence of no external observer is required.

  • BLENDING 2 ALTERNATIVE APPROACHES TO QUANTUM MEASUREMENT

    H NAKAZATO, S PASCAZIO

    PHYSICS LETTERS A   156 ( 7-8 ) 386 - 390  1991.07  [Refereed]

     View Summary

    Two different approaches to the problem of measurement in quantum mechanics are combined. In this way, new insights are obtained into the mechanism engendering the loss of coherence suffered by a quantum mechanical system when interacting with a macroscopic apparatus.

  • Complementarity in the Double-Slit Experiment Revisited : General and Mathematical Physics

    Hiromichi NAKAZATO, Department of Physics University of the Ryukyus

    Progress of theoretical physics = Progress of theoretical physics   85 ( 6 ) 1177 - 1187  1991.06

    DOI CiNii

  • SYMMETRIES IN STOCHASTIC QUANTIZATION AND ITO-STRATONOVICH RELATED INTERPRETATION

    H NAKAZATO, K OKANO, L SCHULKE, Y YAMANAKA

    NUCLEAR PHYSICS B   346 ( 2-3 ) 611 - 631  1990.12  [Refereed]

  • Spectral representation in stochastic quantization

    Nakazato, H.

    Physical Review D   42 ( 4 )  1990

    DOI

    Scopus

    1
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    (Scopus)
  • Calculation of β-Functions Up to Two-Loop Order in φ^4 Theory Based on Stochastic Quantization Method : Particles and Fields

    Hiromichi NAKAZATO, Gentaro TAKADA, Hiroshi SOSHI, Yoshiya YAMANAKA, Department of Physics University of the Ryukyus, Department of Physics Waseda University, Department of Physics Waseda University, Department of Physics University of Alberta

    Progress of theoretical physics = Progress of theoretical physics   80 ( 3 ) 559 - 565  1988.09

    DOI CiNii

  • Thermal Equilibrium in Minkowski Stochastic Quantization

    Hiromichi NAKAZATO, Department of Physics Waseda University

    Progress of theoretical physics = Progress of theoretical physics   77 ( 1 ) 20 - 25  1987.01

    DOI CiNii

  • MINKOWSKI STOCHASTIC QUANTIZATION

    H NAKAZATO, Y YAMANAKA

    PHYSICAL REVIEW D   34 ( 2 ) 492 - 496  1986.07  [Refereed]

    DOI

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    26
    Citation
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  • Possible Nonvanishing Mass of Photon : Particles and Fields

    Hiromichi NAKAZATO, Mikio NAMIKI, Yoshiya YAMANAKA, Kan-ichi YOKOYAMA, Department of Physics Waseda University, Department of Physics Waseda University, Research Institute for Theoretical Phisics Hiroshima University, Research Institute for Theoretical Phisics Hiroshima University

    Progress of theoretical physics = Progress of theoretical physics   75 ( 3 ) 686 - 691  1986.03

    DOI CiNii

  • MASSIVE ABELIAN GAUGE-FIELDS COUPLED WITH NONCONSERVED CURRENTS - RENORMALIZATION SCHEME

    H NAKAZATO, M NAMIKI, Y YAMANAKA, K YOKOYAMA

    PROGRESS OF THEORETICAL PHYSICS   75 ( 1 ) 175 - 191  1986.01  [Refereed]

  • EQUIVALENCE OF STOCHASTIC QUANTIZATION METHOD TO CONVENTIONAL FIELD-THEORIES THROUGH SUPER TRANSFORMATION INVARIANCE

    H NAKAZATO, M NAMIKI, OHBA, I, K OKANO

    PROGRESS OF THEORETICAL PHYSICS   70 ( 1 ) 298 - 307  1983  [Refereed]

  • STOCHASTIC QUANTIZATION METHOD OF FERMION FIELDS

    T FUKAI, H NAKAZATO, OHBA, I, K OKANO, Y YAMANAKA

    PROGRESS OF THEORETICAL PHYSICS   69 ( 5 ) 1600 - 1616  1983  [Refereed]

  • SHORT DISTANCE INTERACTION EFFECTS IN ELASTIC DIFFERENTIAL CROSS-SECTION OF HIGH-ENERGY HADRON-NUCLEUS COLLISIONS

    A NAKAMURA, H NAKAZATO, M NAMIKI

    PROGRESS OF THEORETICAL PHYSICS   70 ( 3 ) 858 - 870  1983  [Refereed]

▼display all

Books and Other Publications

  • ペレス 量子論の概念と手法 ---先端研究へのアプローチ---

    丸善  2001

  • Decoherence and Quantum Measurements

    M. Namiki, S. Pascazio, H. Nakazato( Part: Joint author)

    World Sci. Pub. (Singapore)  1998

  • 翻訳:「量子力学はこうして生まれた」,ジョン・ヘンドリー著

    丸善  1992

Presentations

▼display all

Research Projects

  • Quantum Measurement in Statistical Mechanics and Quantum Information

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2014.04
    -
    2018.03
     

    YUASA Kazuya, NAKAZATO Hiromichi, BURGARTH Daniel, FACCHI Paolo, GIOVANNETTI Vittorio, PASCAZIO Saverio

     View Summary

    “Quantum measurement” is a keyword that distinguishes the quantum world from the classical world. We have explored nontrivial roles of quantum measurement in a variety of subjects. In particular, we have focused on “quantum metrology,” “quantum control,” and “statistical mechanics.” We have developed novel ideas and unique methodologies for quantum metrology and quantum control, contributing to the field of quantum information technology, and have shed light upon the intriguing roles of quantum measurement for the foundations of statistical mechanics.

  • 量子環境物理学

    科学研究費助成事業(早稲田大学)  科学研究費助成事業(基盤研究(C))

    Project Year :

    2010
    -
    2014
     

     View Summary

    本研究課題では,外界(環境系)との相互作用下にある注目量子系の物理を,これまで不問に付されてきた感のある環境系のダイナミクスや量子系のコヒーレンスやエンタングルメントといった量子論的特徴の振る舞いを通して解析し,開いた量子系の理解を深化させることにある.今年度は以下のような課題に取り組んだ.
    ・位相相互作用型スピン(量子系)-ボソン(環境)系の厳密解から環境系に対する力学の再吟味に着手しており,マルコフ・非マルコフ性の特徴付けや環境系の緩和時間に関して興味深い結果が得られるものと期待している.また,回転波近似のもとでの準位間遷移型相互作用をする場合のダイナミクスを,全ハミルトニアンの固有値と固有状態を求めるという観点から試みた.基底状態(真空)と第一励起状態のスペクトラムは既知ではあるが,今回,それらの固有状態の完全性(の一部)を示した.
    ・量子系は,純粋度やフォンノイマンエントロピーなど,1体の物理量の

  • Quantum Coherence and Quantum Measurement

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2009
    -
    2012
     

    YUASA Kazuya, NAKAZATO Hiromichi, BURGARTH Daniel, GIOVANNETTI Vittorio, PASCAZIO Saverio

     View Summary

    Among various features that distinguish the quantum world from the classical world, we have focused on “quantum coherence” and “quantum measurement,” and have explored their interesting interplay. We have worked at a variety of subjects, where quantum measurements play nontrivial roles, not simply capturing quantum coherence, but playing a crucial role for the emergence of quantum coherence, or providing us with unique ways of controlling quantum coherence. Through such research, we have approached the intriguing nature of the quantum-mechanical world and developed unique methodologies useful for quantum-information technologies.

  • Spin blockade from spin channel to quantum dots and its application to qubit

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2008
    -
    2010
     

    YOH Kanji, SUEOKA Kazuhisa, NAKAZATO Hiromichi

     View Summary

    We have investigated surface reaction of Fe electrode and InAs substrate by thermodynamic calculation. We have fabricated a spin transistors with Fe electrode and verified current oscillation which agreed well with theoretical calculation. We have also fabricated an InAs nanowire spin transistor based on Au colloid and observed current oscillation which is presumably originates from spin-orbit interaction. In a spintransistor/quantum dot hybrid structure, we have theoretically demonstrated that spin polarization of 40% would be hard to verify quantum entanglement, but it would be appreciably large signal with 60% spin polarization and clear entanglement would be observable with 80% spin polarization in the spin channel.

  • Quantum dynamics and hierarchy

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2006
    -
    2009
     

    NAKAZATO Hiromichi, YUASA Kazuya, SAVERIO Pascazio, PAOLO Facchi, ANTONINO Messina, GIUSEPPE Compagno, BENEDETTO Militello

     View Summary

    The ultimate purpose of this project is to understand in depth the hierarchical structures seen in the theoretical descriptions of physical systems, by faithfully studying the dynamics in the actual physical processes, to extract key notions that are essential in connecting different layers in the hierarchy. In particular, on the dynamics of microscopic systems under the influence of the environmental system, we have proposed new ideas to keep or recover quantum coherence against environmental disturbances like decoherence or dissipation, applied them to several physical situations and obtained new knowledge on such systems. A hint to understand the relationship between the quantum field theory and the quantum mechanics has also been found.

  • Research on Quantum Field Theory for Finite Space-Time Systems and Dynamics of Quantum Systems

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2001
    -
    2006
     

    OHBA Ichiro, NAKAZATO Hiromichi, YAMANAKA Yoshiya, YUASA Kazuya, OTA Yukihiro, MINE Makoto

     View Summary

    In this project the head investigator, I. Ohba together with Y. Ota quantized the dissipative chaos system applying the method of stochastic state diffusion, and discussed the quantum-classical correspondence quantitatively calculating pseudo-Lyapunov index. Then they developed the semiclassical approximation on the quantum dissipative system. Further, they focused on the quantum computer of nuclear spins in a semiconductor proposed by B. E. Kane, and solved the time-dependent Schrodinger equation rigorously and showed that the inevitable operation error exists in the previously proposed way of construction of the quantum gates.
    H. Nakazato and K. Yuasa reconsidered the quantum Zeno effect including the degrees of freedom of the environment, and found that the "environment" (of finite degrees of freedom)is purified by the Zeno-like measurement in which the frequent sequential measurements are performed on the system. As an application, they showed that the entanglement distillation and initialization of qubits are possible. Further, they developed the method to derive the solution of Lindlbad master equation with the Kraus representation.
    Y. Yamanaka together with one of the member

  • Time development of quantum systems and field theory

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2002
    -
    2005
     

    NAKAZATO Hiromichi, YUASA Kazuya

     View Summary

    In this research project, the temporal evolution of quantum systems, especially that under the influence of the action of quantum measurements, has mainly been investigated.
    As is well known, the temporal behavior of a quantum system is classified into three characteristic stages, i.e., the quadratic (Gaussian) behavior at short times, the exponential decay at intermediate times and the power decay at long times and on the basis of a solvable model, we first demonstrated these characteristics analytically.
    Next, we have proposed a new scheme of driving a quantum system under investigation to a pure state irrespectively of its initial (in general mixed) state, by means of repeated measurements of another quantum system in interaction with the former. A remarkable feature of this method is that the two important notions in this kind of research work, that is, the fidelity and the yield, can be made compatible, the condition which is not easily implemented in many other attempts. Moreover, since its fundamental idea is so simple and general, it retains high flexibility and applicability and in fact, it has been generalized and applied to many different physical situations. Among such

  • Temporal evolution of quantum systems and quantum field theory

    Project Year :

    2002
     
     
     

  • Temporal evolution of quantum systems and quantum field theory

    Project Year :

    2000
     
     
     

  • Micro-macro transition and quantum field theory

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1998
    -
    2000
     

    NAKAZATO Hiromichi, IMAFUKU Kentaro, OHBA Ichiro

     View Summary

    The final goal of this project shall be to understand the behaviors of macroscopic and/or mesoscopic systems consistently from the view point of micro-macro transition and to establish quantum theories for such systems. We have inverstigated several topics that are closely connected to the fundamental issues of quantum mechanics, and here is a summary of the results of the project. 1. We have studied the temporal brhaviors of quantum (unstable) systems to obtain a better understanding of the mechanism of losing the quantum coherence to give exponential decay. 2. A neutron-spin experiment, proposed to test the so-called quantum Zeno effect, has been reanalyzed by taking into account of the possible reflection effect of neutron caused at the boundaries of the magnetic field. It has turned ouf that the effect can become so important that the survival probability of the neutron is completely different from the ideal value. 3. The Nelson stochastic quantization method has been used for extracting information about time in quantum systems. In particular, we have tried to estimate the so-called tunneling time, by applying an oscillating external perturbation to the barrier potential. 4. The stochastic resonance, a phenomenum where a noise can enhance the response to a tiny signal, well known in broad area in classical mechanics, is formulated and analyzed quantum mechanically. 5. A quantum nonlinear optical system is proposed to realize a quantum mechanical analogue of the inverted pendulum in classical mechanins. It is shown that the system, which otherwise produces exponentially growing number of two modes of photons through the nonlinear down-conversion process, can be stabilized by applying periodically a linear coupling between the two modes.

  • Micro-macro transition and quantum field theory

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1998
    -
    1999
     

    NAKAZATO Hiromichi, IMAFUKU Kentaro, OHBA Ichiro

     View Summary

    The final goal of this project shall be to understand the behaviors of macroscopic and/or mesoscopic systems consistently from the view point of micro-macro transition and to establish quantum theories for such systems. We have inverstigated several topics that are closely connected to the fundamental issues of quantum mechanics, and here is a summary of the results of the project. 1. We have studied the temporal brhaviors of quantum (unstable) systems to obtain a better understanding of the mechanism of losing the quantum coherence to give exponential decay. 2. A neutron-spin experiment, proposed to test the so-called quantum Zeno effect, has been reanalyzed by taking into account of the possible reflection effect of neutron caused at the boundaries of the magnetic field. It has turned ouf that the effect can become so important that the survival probability of the neutron is completely different from the ideal value. 3. The Nelson stochastic quantization method has been used for extracting information about time in quantum systems. In particular, we have tried to estimate the so-called tunneling time, by applying an oscillating external perturbation to the barrier potential. 4. T

  • Quantum field theory for macroscopic and mesoscopic systems

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1996
    -
    1998
     

    NAKAZATO Hiromichi, PAOLO Cea, SAVERIO Pascazio, OHBA Ichiro

     View Summary

    The final goal of this project shall be to understand both macroscopic and mesoscopic systems quantum mechanically. We have investigated such topics that are closely connected to some fundamental issues of quantum mechanics with special attention to the physical and mathematical realization of the micro-macro transition. Here is a summary of the project.
    1. We have proposed a solvable dynamical model for the quantum measurement proces and scrutinized the mechanism of emergence of the Wiener stochastic process in the weak-coupling, macroscopic limit. It is shown explicitly taht the free Hamiltonian of the detecting macroscopic system plays the role of the Wiener process, which implies that the stchasticity in this model is ascribed to a quantum mechanical origin. 2. Temporal evolution of quantum systems has been reinvestigated in general. Furthermore, the time development of a wave packet was directly calculated for a simple quantum system, and for the hydrogen system the exact expression of the transition amplitude between different energy levels was derived. In the latter case, the characteristic time scale in the short time region was evaluated and the oscillatory behavior was found to persist in the survival probability. 3. A neutron spin-flip experiment which clarifies the occurrence of the quantum Zeno effect has been proposed and examined experimentally and theoretically. 4. Nelson's version of quantum mechanics has beeb applied to a quantum mechanical particle tunmneling through a potential. The behavior of the particle is numerically simulated and the tunneling time has been estimated. We have also tried to take the possible dissipation effect on such a particle into account in this formalism to obtain more realistic tunneling time.
    5. We summarized our research on the decoherence mechanism in the quantum mechanical measurement process in the book, "Decoherence and Quantum Measurements, " (Singapore, 1998).

  • Quantum field theory for macroscopic and mesoscopic systems

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1996
    -
    1997
     

    NAKAZATO Hiromichi, PAOLO Cea, SAVERIO Pascazio, OHBA Ichiro

     View Summary

    The final goal of this project shall be to understand both macroscopic and mesoscopic systems quantum mechanically. We have investigated such topics that are closely connected to some fundamental issues of quantum mechanics with special attention to the physical and mathematical realization of the micro-macro transition. Here is a summary of the project.
    1. We have proposed a solvable dynamical model for the quantum measurement proces and scrutinized the mechanism of emergence of the Wiener stochastic process in the weak-coupling, macroscopic limit. It is shown explicitly taht the free Hamiltonian of the detecting macroscopic system plays the role of the Wiener process, which implies that the stchasticity in this model is ascribed to a quantum mechanical origin. 2. Temporal evolution of quantum systems has been reinvestigated in general. Furthermore, the time development of a wave packet was directly calculated for a simple quantum system, and for the hydrogen system the exact expression of the transition amplitude between different energy levels was derived. In the latter case, the characteristic time scale in the short time region was evaluated and the oscillatory behavior was fo

  • Nonequilibrium stochastic process as a possible quantization method

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1995
    -
    1997
     

    NAKAZATO Hiromichi, OKANO Keisuke, KANENAGA Masahiko

     View Summary

    The stochastic quantization scheme, proposed by Parisi and Wu, has been so designed as to reproduce ordinary quantum theory in the equilibrium limit of a hypothetical stochastic process w.r.t.the so-called fictitious time. In this project, the possibility of quantizing bottomless systems, classical actions of which are unbounded from below, by means of nonequilibrium stochastic processes has been sought. Some related topics have also been investigated.
    Here is a summary of the project. 1.We have set up a kerneled Langevin equation for the simplest (0-dim.) bottomless system and solved it to obtain its exact solution. The method has been extended to systems with many degrees of freedom and the exact solution of the corresponding Fokker-Planck equation was found. 2.These exact solutions clarify that the hypothetical stochastic processes described by the bottomless actions are of diffusion type and therefore have no equilibrium. At the same time, however, it is shown that they can well reprodece the desired weight function e^<-s>, expected in the path integral quantization, in the appropriate finite region corresponding to a finite fictitious time. 3.The so-called excursion phenomena,

  • 中性子による量子力学の理論的研究

    科学研究費助成事業(早稲田大学)  科学研究費助成事業(重点領域研究)

    Project Year :

    1992
    -
    1996
     

     View Summary

    本研究の主目的は観測・測定過程と干渉現象を一つの現象の両極端と考える立場から、詳細な理論的解析を行うところにある。具体的には、測定過程の場合の検出器及び干渉現象の位相器や吸収物と入射中性子との相互作用に対する理論的モデルを考え、位相相関の喪失すなわち、測定による「波束の収縮」の度合いを定量的に判定するオーダーパラメータ(秩序変数)を計算することである。
    本年度の具体的研究目的は、前年度から続いている検出器モデルを導入した大規模数値実験にあったが、その大部分はすでに論文としてまとめ Phy.Rev.A 誌に掲載された。さらに、吸収効果を入れた数値計算も近く論文としてまとめる予定である。また、量子ゼノン効果への不確定性関係の影響を分析した論文が Phys.Lett.誌と Taiyuan 会議に報告された。量子ゼノン効果は不安定量子系の時間発展と密接な関係があるが、その分析の総合報告も Int.J.OfMod.Physics 誌に掲載された。高エネルギー核反応におけ

  • 確率過程量子化法の動力学的研究

    日本学術振興会  科学研究費助成事業

    Project Year :

    1991
     
     
     

    中里 弘道

  • 確率過程量子化法におけるくりこみ理論とその応用

    日本学術振興会  科学研究費助成事業

    Project Year :

    1986
     
     
     

    中里 弘道

▼display all

Misc

  • Carrier Design and Graduate School Reform for Postadoctoral Fellows and Doctoral Students in Science and Engineering(Network Pages for Professional Development of Physicists)

    Asahi Toru, Nakazato Hiromichi, Suzuki Kiyotaka

      68 ( 9 ) 623 - 627  2013.09

    CiNii

  • 29aEG-3 Measurement of eigenvalues of a density operator using the anti-symmetrizer on multipartite quantum system

    Tanaka T., Kimura G., Nakazato H.

    Meeting abstracts of the Physical Society of Japan   68 ( 1 ) 243 - 243  2013.03

    CiNii

  • 19aAK-11 Minimal Model for Measuring Purity and Dimension of Quantum Systems

    Tanaka T., Kimura G., Nakazato H.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 ) 141 - 141  2012.08

    CiNii

  • 23aED-10 Analysis of nonlocality in multi-qubit system in terms of Bell-type inequality

    Yoshida Motoyuki, Sekiguchi Takafumi, Nakazato Hiromichi

    Meeting abstracts of the Physical Society of Japan   66 ( 2 ) 168 - 168  2011.08

    CiNii

  • Physics of the Quark Gluon Plasma and Professor Namiki

    Ohba Ichiro, Nakazato Hiromichi, Zinovjev Gennady, Muroya Shin, Hirano Tetsufumi

    Butsuri   66 ( 4 ) 258 - 269  2011.04

     View Summary

    Discovery of the strongly correlated quark-gluon plasma at RHIC is based on a hydrodynamical model, which is a macroscopic picture model introduced by Landau to describe a multiple production phenomena. Field theoretical derivation and the applicability conditions of the model were established by the late Professor Mikio Namiki and his collaborators. After reviewing the discussions done by Namiki et al, we briefly survey the physics of sQGP at RHIC from the point of view of a hydrodynamical model.

    CiNii

  • Gaussian, exponential and power-law decays and their time ranges : An analysis based on the Friedrichs model(Perspectives of Nonequilibrium Statistical Physics-The Memory of Professor Shuichi Tasaki-) :

    Nakazato Hiromichi

      97 ( 3 ) 450 - 455  2011

     View Summary

    The time ranges of the three typical decay forms in quantum mechanics, i.e., the Gaussian, exponential and power-law decays, are investigated on the basis of the Friedrichs model. The analysis yields a deeper understanding of the decay dynamics of quantum systems.

    CiNii

  • 23aRF-10 Analysis of nonlocality in 3-qubit system by Svetlichny inequality

    Yoshida Motoyuki, Sekiguchi Takafumi, Nakazato Hiromichi

    Meeting abstracts of the Physical Society of Japan   65 ( 2 ) 108 - 108  2010.08

    CiNii

  • 23aTB-8 Dephasing dynamics of non-interacting 2 qubits

    Yoshimoto Seiya, Unoki Makoto, Kajikawa Kouhei, Nakazato Hiromichi

    Meeting abstracts of the Physical Society of Japan   65 ( 1 ) 209 - 209  2010.03

    CiNii

  • 26pZE-10 Entanglement Generation by Resonant Scattering of Ancilla Qubits

    Yuasa Kazuya, Nakazato Hiromichi, Giovannetti Vittorio, Burgarth Daniel

    Meeting abstracts of the Physical Society of Japan   64 ( 2 ) 81 - 81  2009.08

    CiNii

  • 27pSK-11 Entanglement of Field-Emitted Electrons from a Superconductor

    Yuasa K., Ohba I., Tasaki S., Nakazato H., Facchi Paolo, Fazio Rosario, Pascazio Saverio

    Meeting abstracts of the Physical Society of Japan   64 ( 1 ) 144 - 144  2009.03

    CiNii

  • 20aZD-12 Entanglement Generation by 3D Scattering II

    Yuasa Kazuya, Hida Yuichiro, Nakazato Hiromichi

    Meeting abstracts of the Physical Society of Japan   63 ( 2 ) 99 - 99  2008.08

    CiNii

  • 26aWD-7 Dynamical Formulation of (Anti-)Bunching

    Yuasa K., Ohba I., Tasaki S., Nakazato H., Facchi P., Pascazio S.

    Meeting abstracts of the Physical Society of Japan   63 ( 1 ) 335 - 335  2008.02

    CiNii

  • 23pRG-4 Entanglement formation by Scattering in 3D

    Hida Y., Yuasa K., Nakazato H.

    Meeting abstracts of the Physical Society of Japan   62 ( 2 ) 188 - 188  2007.08

    CiNii

  • 18pWD-11 How to Solve Markovian Master Equations in Operator Forms

    Hida Y., Nakazato H., Yuasa K., Militello B., Napoli A., Messina A.

    Meeting abstracts of the Physical Society of Japan   62 ( 1 ) 250 - 250  2007.02

    CiNii

  • 25pRB-6 Decoherence Effect in a Scheme to Entangle Dinstant Qubits via an Entanglement Mediator

    HIDA Yuichiro, YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   61 ( 2 ) 112 - 112  2006.08

    CiNii

  • 30aXG-6 Derivation of Master Equation via Projection Method in the Presence of Initial Correlation

    Yuasa K., Tasaki S., Nakazato H., Ohba I., Kimura G., Facchi Paolo, Pascazio Saverio

    Meeting abstracts of the Physical Society of Japan   61 ( 1 ) 329 - 329  2006.03

    CiNii

  • 22pWA-7 State Tomography for a Multi-Qubit System via Measurements on a Single Qubit

    OKANO K., YUASA K., NAKAZATO H., YOH K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 ) 90 - 90  2005.08

    CiNii

  • 21pXE-9 Short-Time Scaling Law in a Critical Relaxational Dynamics with a Kernelized Langevin Equation

    Hattori N., Otobe T., Yuasa K., Nakazato H., Okano K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 ) 187 - 187  2005.08

    CiNii

  • Evaluating Critical Exponents through Short-time Scaling based on a Kernelized Langevin Equation

    Otobe T., Hattori N., Yuasa K., Nakazato H., Okano K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 ) 187 - 187  2005.08

    CiNii

  • An Efficient Scheme to Entangle Distant Qubits from an Arbitrary Mixed State(Quantum Field Theories : Fundamental Problems and Applications)

    湯浅 一哉, 中里 弘道

    Soryushiron Kenkyu   111 ( 3 ) C101  2005.06

    DOI CiNii

  • 27aYE-4 An Efficient Scheme to Distill an Entanglement between Distant Qubits

    YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   60 ( 1 ) 178 - 178  2005.03

    CiNii

  • Quantum Zeno effect in an environment

    Yuasa Kazuya, Nakazato Hiromichi

    Bussei Kenkyu   82 ( 6 ) 924 - 928  2004.09

     View Summary

    この論文は国立情報学研究所の電子図書館事業により電子化されました。

    CiNii

  • ゼノン型観測によるエンタングル状態の抽出(場の量子論の基礎的諸問題と応用,研究会報告)

    湯浅 一哉, 中里 弘道, 鵜木 誠

    素粒子論研究   109 ( 6 ) F94  2004.09

    DOI CiNii

  • 15pTF-10 Robustness of a Purification Method based on Zeno-like Measurements against Errors in Measurements

    OKANO Kosuke, UNOKI Makoto, YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   59 ( 2 ) 144 - 144  2004.08

    CiNii

  • 28pXG-8 Purification through Zeno-like measurements : Robustness against fluctuations in measurement intervals

    UNOKI Makoto, YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   59 ( 1 ) 174 - 174  2004.03

    CiNii

  • Purification of Quantum States through Zeno-like Measurements(Quantum Field Theories: Fundamental Problems and Applications)

    湯浅 一哉, 中里 弘道, 高沢 智子

    Soryushiron Kenkyu   107 ( 5 ) E70  2003.08

    DOI CiNii

  • Entanglement Distillation through Zeno-like Measurements

    Nakazato H., Yuasa K., Unoki M.

    Meeting abstracts of the Physical Society of Japan   58 ( 2 ) 149 - 149  2003.08

    CiNii

  • Purification of Quantum States through Zeno-like Measurements

    UNOKI Makoto, YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   58 ( 1 ) 203 - 203  2003.03

    CiNii

  • Fluctuation in time interval of measurements in Quantum Zeno Effect

    UNOKI M, NAKAGURO Y, YUASA K, NAKAZATO H

    Meeting abstracts of the Physical Society of Japan   57 ( 2 ) 218 - 218  2002.08

    CiNii

  • Efficiency of Mirrors in the Neutron-Spin Test of Quantum Zeno Effect

    Nakaguro Y, Unoki M, Yuasa K, Nakazato H, Facchi P, Pascazio S

    Meeting abstracts of the Physical Society of Japan   57 ( 2 ) 218 - 218  2002.08

    CiNii

  • 24pXG-13 環境の影響下における量子ゼノン効果

    湯浅 一哉, 中里 弘道, 高沢 智子

    日本物理学会講演概要集   57 ( 1 ) 3 - 3  2002.03

    CiNii

  • 24pXG-13 Quantum Zeno Effect in an Environment

    YUASA Kazuya, NAKAZATO Hiromichi, TAKAZAWA Tomoko

    Meeting abstracts of the Physical Society of Japan   57 ( 1 ) 123 - 123  2002.03

    CiNii

  • Kernel-dependence in stochastic quantization of bottomless systems

    YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   55 ( 1 ) 1 - 1  2000.03

    CiNii

  • 25aSG-2 Stochastic Quantization of Bottomless Systems of φ^3-Type

    SUGIYAMA Hiroaki, YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   54 ( 2 ) 7 - 7  1999.09

    CiNii

  • 31a-YD-9 Analysis on Stochastic Quantization of Bottomless Systems with Analytical Solution to the Fokker-Planck Equation

    YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   54 ( 1 ) 8 - 8  1999.03

    CiNii

  • 28p-ZD-2 Quantum zeno effect in neutron experiment : Reflection effect

    Machida K., Nakazato H., Pascazio S., Rauch H., Yu S.-X.

    Meeting abstracts of the Physical Society of Japan   54 ( 1 ) 278 - 278  1999.03

    CiNii

  • 絡み合いとデコヒーレンス:量子と古典の境界線(セルジュ・アロッシュ著)

    中里弘道

    パリティ/丸善   14;8,pp.18-26  1999

  • The effect of "fluctuation" in the (modified) Coleman-Hepp model

    OKUMURA M., IMAFUKU K., NAKAZATO H.

    Meeting abstracts of the Physical Society of Japan   53 ( 2 ) 745 - 745  1998.09

    CiNii

  • The Analytical Solution to the Fokker-Planck Equation with a Bottomless Action:Dependence on Initial Condition

    YUASA Kazuya, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   53 ( 2 ) 9 - 9  1998.09

    CiNii

  • 時間とはいったい何だろうか?(2)

    Wheeler John Archibald, 中里 弘道

    パリティ   13 ( 8 ) 21 - 33  1998.08

    CiNii

  • 時間とはいったい何だろうか?(1)

    Wheeler John Archibald, 中里 弘道

    パリティ   13 ( 7 ) 28 - 35  1998.07

    CiNii

  • On time scale in tunneling phenomena

    IMAFUKU Kentaro, NAKAZATO Hiromichi

    Meeting abstracts of the Physical Society of Japan   53 ( 1 ) 659 - 659  1998.03

    CiNii

  • 時間とは一体何だろうか?(I)(ジョン・ウィーラー著)

    中里弘道

    パリティ/丸善   13;7, pp. 28-35  1998

  • 時間とは一体何だろうか?(II)(ジョン・ウィーラー著)

    中里弘道

    パリティ/丸善   13;8, pp. 21-33  1998

  • 5p-YE-13 Emergence of a Wiener process in a dynamical model describing a quantum mechanical interaction with a macroscopic medium

    Biasi R., Nakazato H., Namiki M., Pascazio S.

    Meeting abstracts of the Physical Society of Japan   52 ( 2 ) 735 - 735  1997.09

    CiNii

  • 5p-YE-17 Dissipation affected by 1/f noise in quantum mechanics

    Oyama Hajime, Arazoe Naoki, Machida Ken, Nakazato Hiromichi, Ohba Ichiro

    Meeting abstracts of the Physical Society of Japan   52 ( 2 ) 736 - 736  1997.09

    CiNii

  • 23p-C-10 The Transition Amplitude for the Coulomb System within the Stochastic Quantisation Scheme

    Yuasa Kazuya, Nakazato Hiromichi

    Meeting abstracts of the Physical Society of Japan   52 ( 2 ) 14 - 14  1997.09

    CiNii

  • 31p-YQ-10 Quantum dephasing by a chaotic system with a few degrees of freedom III

    Sasaki Takashi, Nakazato Hiromichi, Namiki Mikio

    Meeting abstracts of the Physical Society of Japan   52 ( 1 ) 17 - 17  1997.03

    CiNii

  • 31p-YQ-9 Time development of the wave packet and its "time delay" in potential scattering

    Nakazato H.

    Meeting abstracts of the Physical Society of Japan   52 ( 1 ) 17 - 17  1997.03

    CiNii

  • 31p-YQ-6 Decoherece of a quantum system coupled with heat bath

    Arazoe Naoki, Nakazato Hiromichi, Ohba Ichiro

    Meeting abstracts of the Physical Society of Japan   52 ( 1 ) 16 - 16  1997.03

    CiNii

  • 30p-A-6 Quantum zeno effect in neutron experiment II

    Machida Ken, Nakazato Hiromichi, Namiki Mikio, Pascazio Saverio

    Meeting abstracts of the Physical Society of Japan   52 ( 1 ) 384 - 384  1997.03

    CiNii

  • 測定による波動関数の位相相関の喪失 : 数値実験と解析(量子情報理論と開放系)

    町田 顕, 河野 尚幸, 中里 弘道

    数理解析研究所講究録   982   21 - 29  1997.03

    CiNii

  • Modified Coleman-Hepp 模型とそのマクロ極限(量子情報理論と開放系)

    Pascazio Saverio, 中里 弘道

    数理解析研究所講究録   980   22 - 31  1997.02

    CiNii

  • 9a-K-7 Transition Amplitudes within the Stochastic Quantization Scheme

    Yuasa Kazuya, Nakazato Hiromichi

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1996 ( 1 ) 29 - 29  1996.09

    CiNii

  • 9a-K-5 Dephasing by a chaotic system with a few degrees of freedom II

    Sasaki Takashi, Nakazato Hiromichi, Namiki Mikio

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1996 ( 1 ) 28 - 28  1996.09

    CiNii

  • Quantum zeno effect in neutron experiment

    Machida Ken, Nakazato Hiromichi, Namiki Mikio, Pascazio Saverio

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1996 ( 2 ) 655 - 655  1996.09

    CiNii

  • 量子力学的測定過程の数値シミュレ-ション (特集 観測問題とその周辺)

    町田 顕, 中里 弘道, Pascazio Saverio

    数理科学   34 ( 2 ) 13 - 18  1996.02

    CiNii

  • 量子力学的測定過程の数値シミュレーション

    町田 顕, 中里 弘道, Pascazio Saverio

    数理科学/サイエンス社   1996年2月号 ( 2 ) 13 - 18  1996

    CiNii

  • 2p-A-1 Application of the Stochastic Quantization to Bottomless Systems

    Nakazato Hiromichi

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1994 ( 1 ) 26 - 26  1994.09

    CiNii

  • V. B. Braginsky and F. Y. Khalili, Quantum Measurement, Cambridge University Press, New York, 1992, xvi+194p., 23.5×15.5cm, 8,480円

    中里 弘道

    日本物理學會誌   49 ( 2 ) 144 - 144  1994.02

    CiNii

  • 6p-C-7 Transition Amplitudes within the Stochastic Quantization Scheme

    NAKAZATO Hiromichi, HUFFEL Helmuth

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1993 ( 1 ) 33 - 33  1993.09

    CiNii

  • Ciniの観測理論と多ヒルベルト空間的アプローチ(量子力学的観測理論,研究会報告)

    Pascazio Saverio, 中里 弘道

    素粒子論研究   83 ( 6 ) F132 - F135  1991.09

     View Summary

    量子力学的測定過程が量子力学の枠内で理解できるか?といういわゆる量子力学的観測問題の解決を目指した試みは数多く存在するが,ここではその中からCiniの観測理論[1]を取り上げ,これにMachida-Namikiの多ヒルベルト空間的アプローチ[2]を適用し,Ciniの測定器にゆらぎの効果を取り入れた場合を考察する.なお,詳しい議論に関しては[3]を参照していただきたい.

    DOI CiNii

  • Application of Minkowski Stochastic Quantization Method to Vector Field Theory

    Hiromichi NAKAZATO, Department of Physics Waseda University

    Progress of theoretical physics = Progress of theoretical physics   77 ( 4 ) 802 - 807  1987.04

    CiNii

  • 27a-JE-4 波束の収縮を起こす観測過程と散乱モデル(統計力学・物性基礎論)

    村山 良昌, 中里 弘道, 並木 美喜雄, 大場 一郎

    年会講演予稿集   42 ( 3 ) 296 - 296  1987.03

    CiNii

  • 30p-QB-13 観測にともなう波束の収縮の数値シミュレーション

    村山 良昌, 中里 弘道, 並木 美喜雄, 大場 一郎

    秋の分科会講演予稿集   1986 ( 3 ) 394 - 394  1986.09

    CiNii

  • "Excited lepton" described by renormalizable field theory

    中里 弘道

    Soryushiron Kenkyu   71 ( 5 ) E61 - E64  1985.08

    CiNii

  • 確率過程量子化法と超対称性(確率過程量子化法をめぐって,研究会報告)

    中里 弘道

    素粒子論研究   71 ( 4 ) D13 - D15  1985.07

    CiNii

  • 確率過程量子化法をめぐって

    中里 弘道

    素粒子論研究   71 ( 4 ) pD11 - D57  1985.07

    CiNii

  • 確率過程量子法と超対称性(原子核三者若手夏の学校,研究会報告)

    中里 弘道

    素粒子論研究   69 ( 2 ) Bp1 - 15  1984.05

    CiNii

  • PHENOMENOLOGICAL ANALYSIS OF Z0-]LL-GAMMA DECAY ON EXCITED LEPTON HYPOTHESIS

    H NAKAZATO, M NAMIKI, Y YAMANAKA, K YOKOYAMA

    PROGRESS OF THEORETICAL PHYSICS   72 ( 4 ) 865 - 868  1984

    Article, review, commentary, editorial, etc. (scientific journal)  

  • Stochastic Quantization Method of Fermion Fields

    NAKAZATO H

    Soryushiron Kenkyu   67 ( 5 ) E16  1983.08

    CiNii

  • 高エネルギー・ハドロン-原子核反応に関するコメント((II)「ハドロン物理」研究会,原子核三者若手夏の学校報告)

    中里 弘道

    素粒子論研究   64 ( 5 ) 235 - 235  1982.02

    CiNii

  • 高エネルギー・ハドロン-原子核散乱の分析(高エネルギー素粒子及び原子核標的反応におけるハドロン生成機構,研究会報告)

    中里 弘道

    素粒子論研究   63 ( 5 ) E82 - E88  1981.08

    DOI CiNii

  • 高エネルギー・ハドロン-原子核散乱におけるVirtuality効果(ハドロン物理とQCD,原子核三者若手夏の学校・研究会報告-素粒子論-,夏の学校報告)

    中里 弘道

    素粒子論研究   62 ( 3 ) 101 - 103  1980.12

    CiNii

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Other

  • Dupty Dean of Research Counsil, Waseda University

    2011.06
     
     
  • 早稲田大学副研究院長(~2014年9月)

    2011.06
     
     
  • Assistant Dean, Faculty of Science and Engineering, Waseda University (-2008 September)

    2006.09
     
     
  • 先進理工学部教務主任(~2008年9月)

    2006.09
     
     
 

Syllabus

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Overseas Activities

  • 量子論の基礎にかかわる諸課題の検討

    2019.10
    -
    2020.03

    イタリア   Palermo University

    イタリア   Bari University

Sub-affiliation

  • Faculty of Science and Engineering   Graduate School of Advanced Science and Engineering

Research Institute

  • 2022
    -
    2024

    Waseda Research Institute for Science and Engineering   Concurrent Researcher

Internal Special Research Projects

  • 量子論の伝統的模型で解き明かす量子ダイナミクス

    2021  

     View Summary

    1. We show that for any finite-dimensionalquantum systems, the conserved quantities can be characterized by theirrobustness to small perturbations: for fragile symmetries, small perturbationscan lead to large deviations over long times, while for robust symmetries,their expectation values remain close to their initial values for all times.This is in analogy with the celebrated Kolmogorov-Arnold-Moser theorem inclassical mechanics. 2. An analytic approach to investigatethe zero-temperature time evolution of the Jaynes-Cummings system with cavitylosses is developed. With realistic coupling between the cavity and theenvironment assumed, a simple master equation is derived, leading to theexplicit analytic solution for the resonant case. We examine the small and large detuning limits and discuss thecondition where the widely used phenomenological treatment is justified.Explicit evaluations of the time evolutions for various initial states withfinite detuning are also presented.3. We propose to extend the adiabatic impulseapproximation to multilevel systems to cope with non-adiabatic transitions seenin various fields of physics. This approximation method is shown to beequivalent to a series of unitary evolutions and facilitates to evaluate the dynamicsnumerically. In particular, we analyze the dynamics of the Landau–Zener gridmodel and the multilevel Landau–Zener–Stueckelberg–Majorana interference model,and confirm that the results are in good agreement with the exact dynamicsevaluated numerically. We also derive the conditions for destructiveinterference to occur in the multilevel system.&nbsp;

  • 新たな知見と視点から探る量子論基礎

    2020  

     View Summary

    First, the time evolution of an arbitraryfinite-dimensional quantum system under frequent kicks, where each kick is ageneric quantum operation, has been considered. &nbsp;We develop a generalization of theBaker-Campbell-Hausdorff formula, allowing to reformulate such pulsed dynamicsas a continuous one. &nbsp;As a result, weobtain a general type of quantum Zeno dynamics, which unifies all knownmanifestations in the literature as well as describing new types.Second, it has been theoretically demonstratedthat two spins (qubits or qutrits), coupled by exchange interaction,undergo a coupling-based joint Landau-Majorana-Stückelberg-Zenertransition when a linear ramp is applied&nbsp; to one of the two spins. &nbsp;Such a transition, under appropriateconditions, drives the two-spin system toward a maximally entangled state. &nbsp;We have investigated effects, on the quantumdynamics of the two qudits, stemming from the Dzyaloshinskii-Moriya (DM) anddipole-dipole (d-d) interactions, qualitatively and quantitatively. &nbsp;Since the Hamiltonian of the two spins has a symmetry, an exact treatment of the quantum dynamics is possible. &nbsp;We have transparently revealed that the DM andd-d interactions generate independent, enhancing or hindering, modifications inthe dynamical behavior predicted for the two spins coupled exclusively by theexchange interaction.

  • 量子2準位系の解析解と量子論基礎

    2019  

     View Summary

    On the basis of the recent proposal for the new parametrization of evolution operators for quantum two-level systems, a protocol for explicitly constructing the exact evolution operators generated by 2×2 time-dependent PT-symmetric Hamiltonians is proposed.&nbsp; Its mathematical applicability is illustrated with the help of appropriate examples. The physical relevance of the proposed approach within gain-loss system scenarios, like two coupled waveguides, is discussed in detail.&nbsp; On the other hand, in the general framework of mixed states, an explicit bound for bipartite NPT entanglement is derived on the basis of the mixedness characterization of the physical system. The result derived is very general, being based only on the assumption of finite dimensionality. In addition it turns out to be of experimental interest since some purity measuring protocols are known. Exploiting the bound in the particular case of thermal entanglement, a way to connect thermodynamic features to monogamy of quantum correlations is suggested, and some recent results on the subject are given a physically clear explanation.

  • 量子ダイナミクスの新展開

    2018  

     View Summary

    In this project, I have examined quantumdynamics of some systems from unique perspectives.&nbsp; In particular, ourrecent proposal of how to construct solvable quantum models for time-dependenttwo-level systems has been applied to a few quantum systems to obtain newinsights and results. We have considered a quantum two-level system (spin 1/2 particle)under a time-dependent classical magnetic field (semi-classical Rabi system) and succeeded in extending the so-called resonance condition to moregeneral one. Our method is applied to a system of a pair oftwo-level systems interacting to each other under external time-dependentmagnetic fields.&nbsp; The total dynamics can be reduced to two independenttwo-dimensional subdynamics only if the total Hamiltonian is endowed with asymmetry.&nbsp; A condition under which a complex quantum four-level system canbe solved analytically has thus been clarified. Our proposal is nothing but a new parametrizationof a solution for time-dependent Hamiltonian systems.&nbsp; This knowledge hasenabled us to parametrize transition amplitudes between instantaneouseigenstates of time-dependent Hamiltonian for quantum two-level system.&nbsp;The result has been utilized to evaluate the quantum adiabatic condition and wehave clarified what was wrong with the traditional adiabatic condition andderived a correct adiabatic condition.

  • 量子ダイナミクスの新展開

    2016  

     View Summary

    In this project, I have examined quantum dynamics of some systems from unique perspectives.&nbsp; First, our recent proposal of how to construct solvable quantum models for time-dependent two-level systems has been applied to a pair of two-level systems interacting to each other under external time-dependent magnetic fields.&nbsp; The system is modeled by a general Hamiltonian endowed with a symmetry that enables one to reduce the total dynamics into two independent two-dimensional subdynamics.&nbsp; Each of the subdynamics is shown to be brought into an exactly solvable form by appropriately engineering the magnetic fields and thus we obtain an exact time evolution of the compound system.&nbsp; Several physically relevant and interesting quantities are evaluated exactly to disclose intriguing phenomena in such a system.&nbsp; On the other hand, it has recently been shown that a strong-amplitude-damping process applied locally on a part of a quantum system can have a beneficial effect on the dynamics of the remaining part of the system.&nbsp; Quantum operations that cannot be implemented without the dissipation become achievable by the action of the strong dissipative process.&nbsp; Here we generalize this idea by identifying decoherence-free subspaces (DFSs) as the subspaces in which the dynamics becomes more complex.&nbsp; We characterize the set of reachable operations within the DFSs.&nbsp; We provide three examples that become fully controllable within the DFSs while the control over the original Hilbert space in the absence of dissipation is trivial.&nbsp; In particular, we show that the (classical) Ising Hamiltonian is turned into a Heisenberg Hamiltonian by strong collective decoherence, which provides universal quantum computation within the DFSs.

  • 量子論の新展開:基礎物理学のニューフロンティア

    2001   相澤 洋二, 大場 一郎, 栗原 進, 前田 恵一, 田崎 秀一, 大師堂 経明, 井元 信之, 家 泰弘, 小林 俊一, 佐藤 勝彦, 中村 勝弘, Pascazio, S., Accardi, L., Casati, G., Berry, M.V., Rauch, H.

     View Summary

    本研究課題は,2002年に開催予定の国際研究集会「早稲田基礎物理学シンポジウム-量子論の新展開-」の企画準備を目的としている.この研究集会では,素粒子のようなミクロな世界から膨張する宇宙まで,広範なスケールでのあらゆる階層の物理現象の中から,特に量子論の基礎とその周辺に焦点を当てて現代基礎物理学の到達点を振り返るとともに,21世紀の基礎物理学の進路を展望する.本研究課題の成果としては,以下に記すような準備のための会合と,関連の準備研究集会(いずれも理工学部内で開催)を設けて,シンポジウムの方向性を定めることができた.準備作業の経緯2001年6月7日 第一回準備会合:国際研究集会を2002年11月13~15日に国際会議場で開催することを決定.組織委員長として大場一郎理工学部教授を選出.会議の名称,招待講演者の可能性等に関して意見交換2001年6月30日 第二回準備会合:学外研究分担者も交えて,会議の骨格作り2001年9月27日~29日 日本-イタリア共同フォーラム 早稲田ワークショップ「量子力学の基礎的問題」に参加2002年1月23日 第三回準備会合:国際研究集会の名称を「早稲田基礎物理学シンポジウム-量子論の新展開-」(英文 "Waseda Symposium on Fundamental Physics --New Perspectives in Quantum Physics--")に決定.Advisory Board,組織委員会及び招待講演候補者の選定と国内準備研究集会を3月に実施することを確認2002年3月18日~19日 国内準備研究集会を開催 2002年3月19日 第四回準備会合:上記研究会を受けて,国内外の招待講演者リスト作成.2002年11月実施に向けた作業の確認

  • 不安定量子系の時間発展

    1998  

     View Summary

     不安定量子系の崩壊における指数関数的振る舞いからのずれを測る実験、あるいは量子論の基礎の吟味をも視野に入れた実験は、近年になって漸く可能になるとともに、今日著しい進展を遂げつつある。これらの実験的状況は理論的興味にも大きく影響を与え、量子ゼノン効果検証実験の理論的解析や陽子崩壊における量子効果の再検討等が始まっている。本研究はこのような流れを踏まえ、不安定系に対する(場の)量子論を再考しその時間発展を詳細に検討するとともに、実験との比較を通して量子論自身を今一度吟味することを最終目的として提案されたが、本年度は、上記の量子ゼノン効果に関して、より現実的な模型に基づく理論解析を行なった。 量子ゼノン効果の検証実験としては、中性子スピンを使った実験が理論的に提案され、それに基づいて現在実際の実験が進行中であるが、この効果の検証のためには、実験上の様々なロスをも考慮したより現実的な解析が必要である。実験では、有限領域内の磁場との相互作用とそれに引き続くスペクトル分解によってスピンのある一成分の時間発展に注目することになるが、これまでの理論解析では、磁場の境界領域でのロス(中性子の反射)が考えられてこなかった。我々は、この反射の効果を取り入れた模型を提案するとともに、その効果を評価した。模型はこれまでと同様、厳密に解くことが可能であり、反射のようなロスが存在する場合には、どのようなスペクトル分解を行なうかで最終的な結果が全く変わってしまうということが判明した。これは実験を行なう上でロスの抑制が極めて重要であることを物語っている。この成果は間もなく公表の予定である。 この他、この課題に関連した問題として、不安定量子系の生成機講を理解するための模型の考察、場の量子論の枠内での崩壊過程の取り扱いの試みとして提案されたMaianiらの模型の吟味を行なっている。

  • マクロ系及びメソスコピック系の量子論

    1996  

     View Summary

     本研究ではマクロ系やメソスコピック系に対する量子論的理解をその最終目的とし、micro-macro transition の実現とその物理的、数学的基礎付けを念頭に、量子力学的観測問題及び関連する諸問題に焦点を当てて取り組んできた。具体的な成果としては、 1. Nakazato-Pascazio によって提案された可解な力学的模型の、弱結合・マクロ極限における詳細な分析を進めることによって、この量子系に指数関数型の振る舞いをもたらすような確率過程( Wiener 過程)が存在すること、またその際 Wiener 過程をもたらす演算子が測定器系の自由 Hamiltonian (Heisenberg 演算子) で与えられることを明らかにした。 2. 量子系の時間発展に関して改めて整理し直し、その振る舞い(時間スケールの短い方から順に、ガウス型、指数関数型、べき関数型)と複素エネルギー平面での解析性について一般的な関係を導出した。 3. 量子ゼノン効果の検証実験として中性子スピンを利用する実験を提案し、その実現に向けての実験的・理論的検討を行った。 4. デルタ関数型ポテンシャルよる波束の散乱を忠実に追跡し、その時間発展の様子を詳細に調べた。この場合の相互作用は到達距離 0 の短距離力であるにも拘らず、散乱後の波束は力が斥力であるか引力であるかによって時間のずれ(time delay or advance)を生ずることが分かった。しかしこの一方で、スピンのような内部自由度をもつ波束のスピン反転ポテンシャルによる散乱の場合には、時間のずれは消滅してしまうことも明らかになった。

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