2022/09/25 更新

写真a

ユアサ カズヤ
湯浅 一哉
所属
理工学術院 先進理工学部
職名
教授
ホームページ

兼担

  • 理工学術院   大学院先進理工学研究科

学内研究所等

  • 2020年
    -
    2022年

    理工学術院総合研究所   兼任研究員

学位

  • 2001年03月   早稲田大学   博士(理学)

経歴

  • 2013年
    -
    継続中

    早稲田大学 先進理工学部   物理学科   教授

  • 2012年
    -
    2013年

    早稲田大学 先進理工学部   物理学科   准教授

  • 2007年
    -
    2012年

    早稲田大学 高等研究所   准教授

  • 2007年
     
     

    イタリア・バーリ大学 物理学科   博士研究員

  • 2006年
    -
    2007年

    独立行政法人産業技術総合研究所 情報セキュリティ研究センター   研究員

  • 2004年
    -
    2006年

    早稲田大学大学院 理工学研究科   物理学及応用物理学専攻   客員講師 (専任扱い)

  • 2001年
    -
    2004年

    早稲田大学 理工学部   物理学科   助手

  • 1998年
    -
    2001年

    早稲田大学 理工学部   物理学科   日本学術振興会特別研究員 (DC)

▼全件表示

 

研究分野

  • 半導体、光物性、原子物理

  • 数理物理、物性基礎

研究キーワード

  • Superconductor

  • Bose-Einstein Condensation

  • Quantum Zeno Effect

  • 量子ゼノン効果

  • 超伝導

  • ボース凝縮

  • 光物性

  • 表面物理

  • Quantum Measurement

  • 量子観測

  • Quantum Field Theory

  • Open Quantum Systems

  • Control of Quantum Systems

  • Quantum Coherence

  • Quantum Information

  • Foundations of Quantum Mechanics

  • 場の量子論

  • 量子開放系

  • 量子系制御

  • 量子コヒーレンス

  • 量子情報

  • 量子論基礎

▼全件表示

論文

  • Unification of Random Dynamical Decoupling and the Quantum Zeno Effect

    Alexander Hahn, Daniel Burgarth, Kazuya Yuasa

    New Journal of Physics   24 ( 6 ) 063027  2022年07月  [査読有り]  [国際誌]  [国際共著]

     概要を見る

    Periodic deterministic bang–bang dynamical decoupling and the quantum Zeno effect are known to emerge from the same physical mechanism. Both concepts are based on cycles of strong and frequent kicks provoking a subdivision of the Hilbert space into independent subspaces. However, previous unification results do not capture the case of random bang–bang dynamical decoupling, which can be advantageous to the deterministic case but has an inherently acyclic structure. Here, we establish a correspondence between random dynamical decoupling and the quantum Zeno effect by investigating the average over random decoupling evolutions. This protocol is a manifestation of the quantum Zeno dynamics and leads to a unitary bath evolution. By providing a framework that we call equitability of system and bath, we show that the system dynamics under random dynamical decoupling converges to a unitary with a decoupling error that characteristically depends on the convergence speed of the Zeno limit. This reveals a unification of the random dynamical decoupling and the quantum Zeno effect.

    DOI

  • One bound to rule them all: from Adiabatic to Zeno

    Daniel Burgarth, Paolo Facchi, Giovanni Gramegna, Kazuya Yuasa

    Quantum   6   737  2022年06月  [査読有り]  [国際誌]  [国際共著]

     概要を見る

    We derive a universal nonperturbative bound on the distance between unitary evolutions generated by time-dependent Hamiltonians in terms of the difference of their integral actions. We apply our result to provide explicit error bounds for the rotating-wave approximation and generalize it beyond the qubit case. We discuss the error of the rotating-wave approximation over long time and in the presence of time-dependent amplitude modulation. We also show how our universal bound can be used to derive and to generalize other known theorems such as the strong-coupling limit, the adiabatic theorem, and product formulas, which are relevant to quantum-control strategies including the Zeno control and the dynamical decoupling. Finally, we prove generalized versions of the Trotter product formula, extending its validity beyond the standard scaling assumption.

    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  2021年04月  [査読有り]  [国際誌]  [国際共著]

    DOI

  • Eternal Adiabaticity in Quantum Evolution

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

    Physical Review A   103 ( 3 ) 032214  2021年03月  [査読有り]  [国際誌]  [国際共著]

    DOI

  • Quantum Zeno Dynamics from General Quantum Operations

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

    Quantum   4   289  2020年07月  [査読有り]  [国際誌]  [国際共著]

     概要を見る

    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

  • Phase Diagram of Bipartite Entanglement

    Paolo Facchi, Giorgio Parisi, Saverio Pascazio, Antonello Scardicchio, Kazuya Yuasa

    Journal of Physics A   52   414002  2019年09月  [査読有り]

    DOI

  • Relaxation to Gaussian Generalized Gibbs Ensembles in Quadratic Bosonic Systems in the Thermodynamic Limit

    Takaaki Monnai, Shohei Morodome, Kazuya Yuasa

    Physical Review E   100   022105  2019年08月  [査読有り]

    DOI

  • Generalized Adiabatic Theorem and Strong-Coupling Limits

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

    Quantum   3   152  2019年06月  [査読有り]

    DOI

  • Optimal Gaussian Metrology for Generic Multimode Interferometric Circuit

    Teruo Matsubara, Paolo Facchi, Vittorio Giovannetti, Kazuya Yuasa

    New Journal of Physics   21   033014  2019年03月  [査読有り]

    DOI

  • Long-Lived Entanglement of Two Multilevel Atoms in a Waveguide

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

    Journal of Physics Communications   2   035006  2018年03月  [査読有り]

    DOI

  • On the Derivation of the GKLS Equation for Weakly Coupled Systems

    Paolo Facchi, Marilena Ligabo, Kazuya Yuasa

    OPEN SYSTEMS & INFORMATION DYNAMICS   24 ( 4 ) 1740017  2017年12月  [査読有り]

     概要を見る

    We consider the reduced dynamics of a small quantum system in interaction with a reservoir when the initial state is factorized. We present a rigorous derivation of a GKLS master equation in the weak-coupling limit for a generic bath, which is not assumed to have a bosonic or fermionic nature, and whose reference state is not necessarily thermal. The crucial assumption is a reservoir state endowed with a mixing property: the n-point connected correlation function of the interaction must be asymptotically bounded by the product of two-point functions (clustering property).

    DOI

  • Estimating Temperature via Sequential Measurements

    Antonella De Pasquale, Kazuya Yuasa, Vittorio Giovannetti

    Physical Review A   96 ( 1 ) 012316  2017年07月  [査読有り]  [国際誌]  [国際共著]

    DOI

  • Lindbladian purification

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

    Quantum Science and Technology   2 ( 2 ) 024001  2017年06月  [査読有り]

     概要を見る

    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

  • Remote parameter estimation in a quantum spin chain enhanced by local control

    Jukka Kiukas, Kazuya Yuasa, Daniel Burgarth

    PHYSICAL REVIEW A   95 ( 5 ) 052132  2017年05月  [査読有り]

     概要を見る

    We study the interplay of control and parameter estimation on a quantum spin chain. A single qubit probe is attached to one end of the chain, while we wish to estimate a parameter on the other end. We find that control on the probe qubit can substantially improve the estimation performance and discover some interesting connections to quantum state transfer.

    DOI

  • 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  2017年03月  [査読有り]

    DOI

  • Uncertainty relations in the framework of equalities

    Tohru Ozawa, Kazuya Yuasa

    JOURNAL OF MATHEMATICAL ANALYSIS AND APPLICATIONS   445 ( 1 ) 998 - 1012  2017年01月  [査読有り]

     概要を見る

    We study the Schrodinger Robertson uncertainty relations in an algebraic framework. Moreover, we show that some specific commutation relations imply new equalities, which are regarded as equality versions of well-known inequalities such as Hardy's inequality. (C) 2016 Elsevier Inc. All rights reserved.

    DOI

  • Typical pure nonequilibrium steady states and irreversibility for quantum transport

    Takaaki Monnai, Kazuya Yuasa

    PHYSICAL REVIEW E   94 ( 1 ) 012146  2016年07月  [査読有り]

     概要を見る

    It is known that each single typical pure state in an energy shell of a large isolated quantum system well represents a thermal equilibrium state of the system. We show that such typicality holds also for nonequilibrium steady states (NESS's). We consider a small quantum system coupled to multiple infinite reservoirs. In the long run, the total system reaches a unique NESS. We identify a large Hilbert space from which pure states of the system are to be sampled randomly and show that the typical pure states well describe the NESS. We also point out that the irreversible relaxation to the unique NESS is important to the typicality of the pure NESS's.

    DOI

  • Universal control induced by noise

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

    PHYSICAL REVIEW A   93 ( 6 ) 062308  2016年06月  [査読有り]

     概要を見る

    On the basis of the quantum Zeno effect, it has been recently shown [D. K. Burgarth et al., Nat. Commun. 5, 5173 (2014)] 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 strength. As a by-product, a subsystem fidelity that can be applied in other optimization problems for open quantum systems is developed.

    DOI

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

    Hiromichi Nakazato, Saverio Pascazio, Magdalena Stobinska, Kazuya Yuasa

    PHYSICAL REVIEW A   93 ( 2 ) 023845  2016年02月  [査読有り]

     概要を見る

    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 - x(2))(-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

  • Hamiltonian purification

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

    JOURNAL OF MATHEMATICAL PHYSICS   56 ( 12 ) 122104  2015年12月  [査読有り]

     概要を見る

    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

  • Quantum estimation via sequential measurements

    Daniel Burgarth, Vittorio Giovannetti, Airi N. Kato, Kazuya Yuasa

    NEW JOURNAL OF PHYSICS   17   113055  2015年11月  [査読有り]

     概要を見る

    The problem of estimating a parameter of a quantum system through a series of measurements performed sequentially on a quantum probe is analyzed in the general setting where the underlying statistics is explicitly non-i.i.d. We present a generalization of the central limit theorem in the present context, which under fairly general assumptions shows that as the number N of measurement data increases the probability distribution of functionals of the data (e.g., the average of the data) through which the target parameter is estimated becomes asymptotically normal and independent of the initial state of the probe. At variance with the previous studies (Guta M 2011 Phys. Rev. A 83 062324; van Horssen Mand Guta M 2015 J. Math. Phys. 56 022109) we take a diagrammatic approach, which allows one to compute not only the leading orders in N of the moments of the average of the data but also those of the correlations among subsequent measurement outcomes. In particular our analysis points out that the latter, which are not available in usual i.i.d. data, can be exploited in order to improve the accuracy of the parameter estimation. An explicit application of our scheme is discussed by studying how the temperature of a thermal reservoir can be estimated via sequential measurements on a quantum probe in contact with the reservoir.

    DOI

  • Two-mode bosonic quantum metrology with number fluctuations

    Antonella De Pasquale, Paolo Facchi, Giuseppe Florio, Vittorio Giovannetti, Koji Matsuoka, Kazuya Yuasa

    PHYSICAL REVIEW A   92 ( 4 ) 042115  2015年10月  [査読有り]

     概要を見る

    We search for the optimal quantum pure states of identical bosonic particles for applications in quantum metrology, in particular, in the estimation of a single parameter for the generic two-mode interferometric setup. We consider the general case in which the total number of particles is fluctuating around an average N with variance Delta N-2. By recasting the problem in the framework of classical probability, we clarify themaximal accuracy attainable and show that it is always larger than the one reachable with a fixed number of particles (i.e., Delta N = 0). In particular, for larger fluctuations, the error in the estimation diminishes proportionally to 1/Delta N, below the Heisenberg-like scaling 1/N. We also clarify the best input state, which is a quasi-NOON state for a generic setup and, for some special cases, a two-mode Schrodinger-cat state with a vacuum component. In addition, we search for the best state within the class of pure Gaussian states with a given average N, which is revealed to be a product state (with no entanglement) with a squeezed vacuum in one mode and the vacuum in the other.

    DOI

  • 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  2014年11月  [査読有り]

     概要を見る

    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

  • 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  2014年10月  [査読有り]

     概要を見る

    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

  • Typical pure nonequilibrium steady states

    Takaaki Monnai, Kazuya Yuasa

    EPL   107 ( 4 ) 40006  2014年08月  [査読有り]

     概要を見る

    We show that typicality holds for a class of nonequilibrium systems, i.e., nonequilibrium steady states (NESSs): almost all the pure states properly sampled from a certain Hilbert space well represent a NESS and characterize its intrinsic thermal nature. We clarify the relevant Hilbert space from which the pure states are to be sampled, and construct practically all the typical pure NESSs. The scattering approach leads us to the natural extension of the typicality for equilibrium systems. Each pure NESS correctly yields the expectation values of observables given by the standard ensemble approach. It means that we can calculate the expectation values in a NESS with only a single pure NESS. We provide an explicit construction of the typical pure NESS for a model with two reservoirs, and see that it correctly reproduces the Landauer-type formula for the current flowing steadily between the reservoirs. Copyright (C) EPLA, 2014

    DOI

  • 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  2014年06月  [査読有り]

     概要を見る

    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

  • Identifiability of open quantum systems

    Daniel Burgarth, Kazuya Yuasa

    PHYSICAL REVIEW A   89 ( 3 ) 030302(R)  2014年03月  [査読有り]

     概要を見る

    We provide a general framework for the identification of open quantum systems. By looking at the input-output behavior, we try to identify the system inside a black box in which some Markovian time evolution takes place. Due to the generally irreversible nature of the dynamics, it is difficult to assure full controllability over the system. Still, we show that the system is identifiable up to similarity under a certain rank condition. The framework also covers situations relevant to standard quantum process tomography, where we do not have enough control over the system but have a tomographically complete set of initial states and observables. Remarkably, the similarity cannot in general be reduced to unitarity even for unitary systems, and the spectra of Hamiltonians are not identifiable without additional knowledge.

    DOI

  • 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  2013年10月  [査読有り]

     概要を見る

    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

  • 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年09月  [査読有り]

    DOI

  • Ergodic and mixing quantum channels in finite dimensions

    D. Burgarth, G. Chiribella, V. Giovannetti, P. Perinotti, K. Yuasa

    New Journal of Physics   15   073045  2013年07月  [査読有り]

     概要を見る

    The paper provides a systematic characterization of quantum ergodic and mixing channels in finite dimensions and a discussion of their structural properties. In particular, we discuss ergodicity in the general case where the fixed point of the channel is not a full-rank (faithful) density matrix. Notably, we show that ergodicity is stable under randomizations, namely that every random mixture of an ergodic channel with a generic channel is still ergodic. In addition, we prove several conditions under which ergodicity can be promoted to the stronger property of mixing. Finally, exploiting a suitable correspondence between quantum channels and generators of quantum dynamical semigroups, we extend our results to the realm of continuous-time quantum evolutions, providing a characterization of ergodic Lindblad generators and showing that they are dense in the set of all possible generators. © IOP Publishing and Deutsche Physikalische Gesellschaft.

    DOI

  • Entropy-driven phase transitions of entanglement

    Paolo Facchi, Giuseppe Florio, Giorgio Parisi, Saverio Pascazio, Kazuya Yuasa

    Physical Review A - Atomic, Molecular, and Optical Physics   87 ( 5 ) 052324  2013年05月  [査読有り]

     概要を見る

    We study the behavior of bipartite entanglement at fixed von Neumann entropy. We look at the distribution of the entanglement spectrum, that is, the eigenvalues of the reduced density matrix of a quantum system in a pure state. We report the presence of two continuous phase transitions, characterized by different entanglement spectra, which are deformations of classical eigenvalue distributions. © 2013 American Physical Society.

    DOI

  • Witnessing the quantumness of a single system: From anticommutators to interference and discord

    Rosario Fazio, Kavan Modi, Saverio Pascazio, Vlatko Vedral, Kazuya Yuasa

    Physical Review A - Atomic, Molecular, and Optical Physics   87 ( 5 ) 052132  2013年05月  [査読有り]

     概要を見る

    We introduce a method to witness the quantumness of a system. The method relies on the fact that the anticommutator of two classical states is always positive. By contrast, we show that there is always a nonpositive anticommutator due to any two quantum states. We notice that interference depends on the trace of the anticommutator of two states, and it is therefore operationally more suitable to detect quantumness by looking at anticommutators of states rather than their commutators. © 2013 American Physical Society.

    DOI

  • Entropy-driven phase transitions of entanglement

    Paolo Facchi, Giuseppe Florio, Giorgio Parisi, Saverio Pascazio, Kazuya Yuasa

    PHYSICAL REVIEW A   87 ( 5 )  2013年05月  [査読有り]

     概要を見る

    We study the behavior of bipartite entanglement at fixed von Neumann entropy. We look at the distribution of the entanglement spectrum, that is, the eigenvalues of the reduced density matrix of a quantum system in a pure state. We report the presence of two continuous phase transitions, characterized by different entanglement spectra, which are deformations of classical eigenvalue distributions.

    DOI

  • Selective writing and read-out of a register of static qubits

    A. De Pasquale, F. Ciccarello, K. Yuasa, V. Giovannetti

    NEW JOURNAL OF PHYSICS   15   043012  2013年04月  [査読有り]

     概要を見る

    We propose a setup comprising an arbitrarily large array of static qubits (SQs), which interact with a flying qubit (FQ). The SQs work as a quantum register, which can be written or read out by means of the FQ through quantum state transfer (QST). The entire system, including the FQ's motional degrees of freedom, behaves quantum mechanically. We demonstrate a strategy allowing for selective QST between the FQ and a single SQ chosen from the register. This is achieved through a perfect mirror located beyond the SQs and suitable modulation of the inter-SQ distances.

    DOI

  • Classical to quantum in large-number limit

    Kavan Modi, Rosario Fazio, Saverio Pascazio, Vlatko Vedral, Kazuya Yuasa

    PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES   370 ( 1976 ) 4810 - 4820  2012年10月  [査読有り]  [招待有り]

     概要を見る

    We construct a quantumness witness following the work of Alicki & van Ryn (AvR). We reformulate the AvR test by defining it for quantum states rather than for observables. This allows us to identify the necessary quantities and resources to detect quantumness for any given system. The first quantity turns out to be the purity of the system. When applying the witness to a system with even moderate mixedness, the protocol is unable to reveal any quantumness. We then show that having many copies of the system leads the witness to reveal quantumness. This seems contrary to the Bohr correspondence, which asserts that, in the large-number limit, quantum systems become classical, whereas the witness shows quantumness when several non-quantum systems, as determined by the witness, are considered together. However, the resources required to detect the quantumness increase dramatically with the number of systems. We apply the quantumness witness for systems that are highly mixed but in the large-number limit that resembles nuclear magnetic resonance (NMR) systems. We make several conclusions about detecting quantumness in NMR-like systems.

    DOI PubMed

  • Probing Cooper pairs with Franson interferometry

    Vittorio Giovannetti, Kazuya Yuasa

    PHYSICAL REVIEW B   86 ( 11 ) 115429  2012年09月  [査読有り]

     概要を見る

    A setup based on the Franson optical interferometer is analyzed, which allows us to detect the coherence properties of Cooper pairs emerging via tunneling from a superconductor in contact with two one-dimensional channels. By tuning the system parameters we show that both the internal coherence of the emitted Cooper pairs, which is proportional to Pippard's length, and the de Broglie wavelength of their center-of-mass motion can be measured via current-current correlation measurements.

    DOI

  • 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  2012年04月  [査読有り]

     概要を見る

    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

  • Entanglement-assisted tomography of a quantum target

    A. De Pasquale, P. Facchi, V. Giovannetti, K. Yuasa

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   45 ( 10 ) 105309  2012年03月  [査読有り]

     概要を見る

    We study the efficiency of quantum tomographic reconstruction where the system under investigation (quantum target) is indirectly monitored by looking at the state of a quantum probe that has been scattered off the target. In particular, we focus on the state tomography of a qubit through a one-dimensional scattering of a probe qubit, with a Heisenberg-type interaction. Via direct evaluation of the associated quantum Cramer-Rao bounds, we compare the accuracy efficiency that one can obtain by adopting entanglement-assisted strategies with that achievable when entanglement resources are not available. Even though sub-shot noise accuracy levels are not attainable, we show that quantum correlations play a significant role in the estimation. A comparison with the accuracy levels obtainable by direct estimation (not through a probe) of the quantum target is also performed.

    DOI

  • Quantumness and entanglement witnesses

    Paolo Facchi, Saverio Pascazio, Vlatko Vedral, Kazuya Yuasa

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   45 ( 10 ) 105302  2012年03月  [査読有り]

     概要を見る

    We analyze the recently introduced notion of quantumness witnesses and compare it to that of entanglement witnesses. We show that any entanglement witness is also a quantumness witness. We then consider some physically relevant examples and explicitly construct some witnesses.

    DOI

  • Quantum System Identification

    Daniel Burgarth, Kazuya Yuasa

    PHYSICAL REVIEW LETTERS   108 ( 8 ) 080502  2012年02月  [査読有り]

     概要を見る

    The aim of quantum system identification is to estimate the ingredients inside a black box, in which some quantum-mechanical unitary process takes place, by just looking at its input-output behavior. Here we establish a basic and general framework for quantum system identification, that allows us to classify how much knowledge about the quantum system is attainable, in principle, from a given experimental setup. We show that controllable closed quantum systems can be estimated up to unitary conjugation. Prior knowledge on some elements of the black box helps the system identification. We present an example in which a Bell measurement is more efficient to identify the system. When the topology of the system is known, the framework enables us to establish a general criterion for the estimability of the coupling constants in its Hamiltonian.

    DOI

  • 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 ) 075503  2011年04月  [査読有り]

     概要を見る

    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.

    DOI

  • Relevance of Bose-Einstein condensation to the interference of two independent Bose gases

    Mauro Iazzi, Kazuya Yuasa

    PHYSICAL REVIEW A   83 ( 3 ) 033611  2011年03月  [査読有り]

     概要を見る

    Interference of two independently prepared ideal Bose gases is discussed, on the basis of the idea of measurement-induced interference. It is known that, even if the number of atoms in each gas is individually fixed finite and the symmetry of the system is not broken, an interference pattern is observed on each single snapshot. The key role is played by the Hanbury Brown and Twiss effect, which leads to an oscillating pattern of the cloud of identical atoms. Then, how essential is the Bose-Einstein condensation to the interference? In this work, we describe two ideal Bose gases trapped in two separate three-dimensional harmonic traps at a finite temperature T, using the canonical ensembles (with fixed numbers of atoms). We compute the full statistics of the snapshot profiles of the expanding and overlapping gases released from the traps. We obtain a simple formula valid for finite T, which shows that the average fringe spectrum (average fringe contrast) is given by the purity of each gas. The purity is known to be a good measure of condensation, and the formula clarifies the relevance of the condensation to the interference. The results for T = 0, previously known in the literature, can be recovered from our analysis. The fluctuation of the interference spectrum is also studied, and it is shown that the fluctuation is vanishingly small only below the critical temperature T-c, meaning that interference pattern is certainly observed on every snapshot below T-c. The fact that the number of atoms is fixed in the canonical ensemble is crucial to this vanishing fluctuation.

    DOI

  • INTERFERENCE OF AN ARRAY OF INDEPENDENT BOSE-EINSTEIN CONDENSATES WITH FIXED NUMBER OF ATOMS

    Satoshi Ando, Kazuya Yuasa, Mauro Iazzi

    INTERNATIONAL JOURNAL OF QUANTUM INFORMATION   9   431 - 443  2011年01月  [査読有り]

     概要を見る

    Interference of an array of independent Bose-Einstein condensates, whose experiment has been performed recently, is theoretically studied in detail. Even if the number of the atoms in each gas is kept finite and the phases of the gases are not well-defined, interference fringes are observed on each snapshot. The statistics of the snapshot interference patterns, i.e. the average fringe amplitudes and their fluctuations (covariance), are computed analytically, and concise formulas for their asymptotic values for long time of flight are derived. Processes contributing to these quantities are clarified and the relationship with the description on the basis of the symmetry-breaking scenario is revealed.

    DOI

  • 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 ) 060101  2010年12月  [査読有り]

     概要を見る

    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.

    DOI

  • Distillation by repeated measurements: Continuous spectrum case

    Bruno Bellomo, Giuseppe Compagno, Hiromichi Nakazato, Kazuya Yuasa

    PHYSICAL REVIEW A   82 ( 6 )  2010年12月  [査読有り]

     概要を見る

    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.

    DOI

  • Interference of Cooper pairs emitted from independent superconductors

    Mauro Iazzi, Kazuya Yuasa

    PHYSICAL REVIEW B   81 ( 17 ) 172501  2010年05月  [査読有り]

     概要を見る

    We discuss the interference in the two-particle distribution of the electrons emitted from two independent superconductors. It is clarified that, while the interference appearing in the antibunching correlation is due to the Hanbury Brown and Twiss effect, that in the positive correlation due to superconductivity is intrinsically different and is nothing but the first-order interference of Cooper pairs emitted from different sources. This is the equivalent of the interference of two independent Bose-Einstein condensates.

    DOI

  • Extraction of an entanglement by repetition of the resonant transmission of an ancilla qubit

    Kazuya Yuasa

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   43 ( 9 ) 095304  2010年03月  [査読有り]

     概要を見る

    A scheme for the extraction of entanglement in two noninteracting qubits (spins) is proposed. The idea is to make use of the resonant transmission of an ancilla qubit through the two fixed qubits, controlled by the entanglement in the scatterers. Repetition of the resonant transmission extracts the singlet state in the target qubits from their arbitrary given state. Neither the preparation nor the post-selection of the ancilla spin is required, in contrast to the previously proposed schemes.

    DOI

  • 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年  [査読有り]

     概要を見る

    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

  • Thwarted dynamics by partial projective measurements

    Bruno Bellomo, Giuseppe Compagno, Hiromichi Nakazato, Kazuya Yuasa

    Journal of Russian Laser Research   30 ( 5 ) 451 - 457  2009年12月  [査読有り]

     概要を見る

    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. © 2009 Springer Science+Business Media, Inc.

    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   123027  2009年12月  [査読有り]

     概要を見る

    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.

    DOI

  • State tomography of a qubit through scattering of a probe qubit

    Antonella De Pasquale, Kazuya Yuasa, Hiromichi Nakazato

    Physical Review A - Atomic, Molecular, and Optical Physics   80 ( 5 ) 052111  2009年11月  [査読有り]

     概要を見る

    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. © 2009 The American Physical Society.

    DOI

  • 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 ) 052113  2009年11月  [査読有り]

     概要を見る

    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

  • State tomography of a qubit through scattering of a probe qubit

    Antonella De Pasquale, Kazuya Yuasa, Hiromichi Nakazato

    PHYSICAL REVIEW A   80 ( 5 )  2009年11月  [査読有り]

     概要を見る

    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

  • Quantum coherence of electrons field-emitted from a superconductor: Correlations and entanglement

    Kazuya Yuasa

    PHYSICAL REVIEW B   80 ( 10 ) 104516  2009年09月  [査読有り]

     概要を見る

    The correlations of the electrons field-emitted from a superconductor are fully analyzed, both in space and time. It is proposed that a coincidence experiment would reveal a positive correlation between the electrons emitted in opposite directions. The electrons can be entangled and can even violate Bell's inequality. The crucial role played by Andreev's process is scrutinized, analytical formulas are derived for the correlations, and the physics behind the phenomenon is clarified.

    DOI

  • Entanglement generation by qubit scattering in three dimensions

    Yuichiro Hida, Hiromichi Nakazato, Kazuya Yuasa, Yasser Omar

    PHYSICAL REVIEW A   80 ( 1 ) 012310  2009年07月  [査読有り]

     概要を見る

    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

  • 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年05月  [査読有り]

     概要を見る

    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

  • Analysis of Critical Short-Time Langevin Dynamics in Two-Dimensional φ4 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年05月  [査読有り]

    DOI

  • 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年02月  [査読有り]

     概要を見る

    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

  • XX model on the circle

    A. De Pasquale, G. Costantini, P. Facchi, G. Florio, S. Pascazio, K. Yuasa

    EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS   160   127 - 138  2008年07月  [査読有り]

     概要を見る

    We diagonalize the XX model with a finite number of spins and periodic boundary conditions. We solve for the ground state, focus on the rapidity of the convergence to the thermodynamic limit and study the features of multipartite entanglement.

    DOI

  • Crystallographic coherent lengths of J-aggregates and their absorption spectra

    Noritaka Kato, Ichiro Hirosawa, Masup Sato, Tomoyuki Koganezawa, Kazuya Yuasa

    COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS   321 ( 1-3 ) 275 - 280  2008年05月  [査読有り]

     概要を見る

    The Langmuir (L) and Langmuir-Blodgett (LB) films of the J-aggregates formed by amphiphilic merocyanine dye (MID) differ their absorption bands (J-bands), and the J-band in the LB film is located in shorter wavelength than that in the L film. From the grazing incidence X-ray diffraction patterns, the lattice structures and the crystallographic coherent lengths of the MD J-aggregates in the L and LB films were evaluated. Besides a 7% shrinkage of the 2-dimensional lattice in the LB film, more than two-order of magnitude shorter coherent lengths were observed in the LB film, suggesting that the difference of the J-band wavelength was attributed to the size effect of the J-aggregate crystal. (C) 2008 Elsevier B.V. All rights reserved.

    DOI

  • 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 ) 042109  2008年04月  [査読有り]

     概要を見る

    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

  • Estimation of the repeatedly projected reduced density matrix under decoherence

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

    PHYSICAL REVIEW A   77 ( 4 ) 042114  2008年04月  [査読有り]

     概要を見る

    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

  • Lateral effects in fermion antibunching

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

    PHYSICAL REVIEW A   77 ( 4 ) 043623  2008年04月  [査読有り]

     概要を見る

    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

  • 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 ) 042110  2007年10月  [査読有り]

     概要を見る

    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

  • 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年08月  [査読有り]

     概要を見る

    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

  • 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年03月  [査読有り]

     概要を見る

    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

  • 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年03月  [査読有り]

     概要を見る

    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

  • Resonant scattering can enhance the degree of entanglement

    Kazuya Yuasa, Hiromichi Nakazato

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   40 ( 2 ) 297 - 308  2007年01月  [査読有り]

     概要を見る

    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

  • 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年  [査読有り]

     概要を見る

    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

  • 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 ) 062113  2006年12月  [査読有り]

     概要を見る

    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

  • Generation of multipartite entangled states in Josephson architectures

    Rosanna Migliore, Kazuya Yuasa, Hiromichi Nakazato, Antonino Messina

    PHYSICAL REVIEW B   74 ( 10 )  2006年09月  [査読有り]

     概要を見る

    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

  • 斜入射X線回折法による水面上J会合体単分子膜の構造解析とその励起子吸収帯のエネルギー準位の計算

    加藤徳剛, 湯浅一哉, 上江洲由晃

    表面科学   27 ( 5 ) 258 - 264  2006年05月  [査読有り]  [招待有り]

    DOI CiNii

  • A Purification Scheme and Entanglement Distillations

    Hiromichi Nakazato, Makoto Unoki, Kazuya Yuasa

    Quantum Information and Computing, Vol. 19 of QP-PQ: Quantum Probability and White Noise Analysis     259 - 273  2006年03月  [査読有り]

  • Preparation of quantum state through Zeno-like measurements

    Kazuya Yuasa, Hiromichi Nakazato

    THIRD 21COE SYMPOSIUM: ASTROPHYSICS AS INTERDISCIPLINARY SCIENCE   31   183 - +  2006年

     概要を見る

    We present a novel method for preparing pure quantum states, i.e., purification through Zeuo-like measurements, and its possible applications and extensions.

    DOI

  • 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年  [査読有り]

     概要を見る

    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

  • _

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

    素粒子論研究   113 ( 1 ) A15  2006年

    DOI CiNii

  • _

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

    素粒子論研究   113 ( 1 ) A58  2006年

    DOI CiNii

  • 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年11月  [査読有り]

     概要を見る

    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

  • 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年09月  [査読有り]

     概要を見る

    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

  • Determination of a merocyanine J-aggregate structure and the significant contribution of the electric dipole interaction to the exciton band wavelength

    N Kato, K Yuasa, T Araki, Hirosawa, I, M Sato, N Ikeda, K Iimura, Y Uesu

    PHYSICAL REVIEW LETTERS   94 ( 13 ) 136404  2005年04月  [査読有り]

     概要を見る

    The molecular alignment of a merocyanine (MC) J-aggregate monolayer at the air-water interface was determined by a grazing incidence x-ray diffraction method. The obtained molecular arrangement apparently shows that the conventional formula, which accounts only for the transition dipole interaction, is not sufficient to figure out the exciton band wavelength, suggesting the importance of the electric dipole (ED) interaction. We derived a simple formula for the ED interaction energy under an extended dipole approximation and clarified the ED contribution in the MC J aggregate.

    DOI

  • Grazing Incidence X-Ray Diffraction of Merocyanine J-Aggregate Monolayers at the Air-Water Interface

    Noritaka Kato, Kazuya Yuasa, Takeshi Araki, Yoshiaki Uesu, Ichiro Hirosawa, Masugu Sato, Naoshi Ikeda, Ken-ichi Iimura

    Transactions of the Materials Research Society of Japan   30   117 - 121  2005年04月  [査読有り]

  • 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 ) 052316  2004年11月  [査読有り]

     概要を見る

    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

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

    H Nakazato, M Unoki, K Yuasa

    PHYSICAL REVIEW A   70 ( 1 )  2004年07月  [査読有り]

     概要を見る

    A method of purification, purification through Zeno-like measurements [ H. Nakazato, T. Takazawa, and K. Yuasa, Phys. Rev. Lett. 90, 060401 (2003) ], is discussed extensively and applied to a few simple qubit systems. It is explicitly demonstrated how it works and how it is optimized. As possible applications, schemes for initialization of multiple qubits and entanglement purification are presented, and their efficiency is investigated in detail. Simplicity and flexibility of the idea allow us to apply it to various kinds of settings in quantum information and computation, and would provide us with useful and practical methods of state preparation.

    DOI

  • Entanglement purification through Zeno-like measurements

    K Yuasa, H Nakazato, M Unoki

    JOURNAL OF MODERN OPTICS   51 ( 6-7 ) 1005 - 1009  2004年04月  [査読有り]

     概要を見る

    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年  [査読有り]

     概要を見る

    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

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

    Ichiro Ohba, Yoji Aizawa, Tsuneaki Daishido, Susumu Kurihara, Kei-ichi Maeda, Hiromichi Nakazato, Shuichi Tasaki, Kazuya Yuasa

    Journal of the Physical Society of Japan   72 ( Suppl. C ) 1 - 200  2003年12月  [査読有り]

  • 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 ) 012107  2003年07月  [査読有り]

     概要を見る

    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

  • Purification through Zeno-like measurements

    H Nakazato, T Takazawa, K Yuasa

    PHYSICAL REVIEW LETTERS   90 ( 6 ) 060401  2003年02月  [査読有り]

     概要を見る

    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

  • Purification of quantum state through Zeno-like measurements

    Kazuya Yuasa, Hiromichi Nakazato, Tomoko Takazawa

    Journal of the Physical Society of Japan   72 ( C ) 34 - 37  2003年  [査読有り]

     概要を見る

    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. © 2003 The Physical Society of Japan.

    DOI

  • Modified Fowler-Nordheim field emission formulae from a nonplanar emitter model

    K Yuasa, A Shimoi, Ohba, I, C Oshima

    SURFACE SCIENCE   520 ( 1-2 ) 18 - 28  2002年11月  [査読有り]

     概要を見る

    Field emission formulae, current-voltage characteristics and energy distribution of emitted electrons, are derived analytically for a nonplanar (hyperboloidal) metallic emitter model. The traditional Fowler-Nordheim (F-N) formulae, which are derived from a planar emitter model, are modified, and the assumption of the planar emitter in the F-N model is reconsidered. Our analytical calculation also reveals the backgrounds of the previous numerical discussion by He et al. on the effect of the geometry of emitter on field emission. The new formulae contain a parameter which characterizes the sharpness of the hyperboloidal emitter, and experimental data of field emissions from clean tungsten emitters and nanotip emitters are analyzed by making use of this feature. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI CiNii

  • Bifurcation phenomenon in spin relaxation (vol 89, art no 140403, 2002)

    G Kimura, K Yuasa, K Imafuku

    PHYSICAL REVIEW LETTERS   89 ( 16 )  2002年10月

    DOI

  • Bifurcation phenomenon in spin relaxation

    G Kimura, K Yuasa, K Imafuku

    PHYSICAL REVIEW LETTERS   89 ( 14 ) 140403  2002年09月  [査読有り]

     概要を見る

    Spin relaxation in a strong-coupling regime (with respect to the spin system) is investigated in detail based on the spin-boson model in a stochastic limit. We find a bifurcation phenomenon in temperature dependence of relaxation constants, which is never observed in the weak-coupling regime. We also discuss inequalities among the relaxation constants in our model and show the well-known relation 2Gamma(T)greater than or equal toGamma(L), for example, for a wider parameter region than before.

    DOI

  • 2次元量子Markov過程と緩和定数(量子情報とその周辺分野の解析的研究)

    木村, 元, 湯浅, 一哉, 今福, 健太郎

    数理解析研究所講究録   1266   21 - 30  2002年05月

  • Stochastic limit approximation for rapidly decaying systems

    G Kimura, K Yuasa, K Imafuku

    PHYSICAL REVIEW A   63 ( 2 ) 022103  2001年02月  [査読有り]

     概要を見る

    The stochastic limit approximation method for "rapid" decay is presented, where the damping rate gamma is comparable to the system frequency Omega, i.e., gamma similar to Omega, whereas the usual stochastic limit approximation is applied only to the weak damping situation gamma much less than Omega. The key formulas for rapid decay are very similar to those for weak damping, but the dynamics are quite different. From a microscopic Hamiltonian, the spin-boson model, a Bloch equation containing two independent time scales is derived. This is a useful method to extract the minimal dissipative dynamics at high temperature k(B)T much greater than(h) over bar Omega and the master equations obtained are of the Lindblad form unlike that of Caldeira and Leggett. The validity of the method is confirmed by comparing the master equation derived through this method with the exact one.

    DOI CiNii

  • Stochastic Limit Approximation for Rapidly Decaying Systems

    湯浅 一哉, 木村 元, 今福 健太郎

    素粒子論研究   103 ( 1 ) A124 - A129  2001年

    DOI CiNii

  • 量子ホワイトノイズによる量子確率共鳴現象 (量子情報と量子カオスの数理)

    湯浅, 一哉, 今福, 健太郎

    数理解析研究所講究録   1142   100 - 110  2000年04月

    CiNii

  • 24aZB-4 Lindblad型マスター方程式を用いた確率共鳴現象の解析 II

    中村 桂一, 湯浅 一哉, 今福 健太郎, 大場 一郎

    日本物理学会講演概要集   55.1.2   225  2000年

    DOI CiNii

  • 23aTE-5 スピン・ボソン・モデルに基づく速いスピン緩和の解析

    木村 元, 湯浅 一哉, 今福 健太郎

    日本物理学会講演概要集   55.2.2   217  2000年

    DOI CiNii

  • Stochastic quantization of bottomless systems - Stationary quantities in a diffusive process

    K Yuasa, H Nakazato

    PROGRESS OF THEORETICAL PHYSICS   102 ( 4 ) 719 - 727  1999年10月  [査読有り]

     概要を見る

    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 CiNii

  • 27aQ-12 Lindblad型マスター方程式を用いた確率共鳴現象の解析

    中村 桂一, 湯浅 一哉, 今福 健太郎, 大場 一郎

    日本物理学会講演概要集   54.2.2   275  1999年

    DOI CiNii

  • 25p-H-5 スピン-ボソン系における確率共鳴現象について

    今福 健太郎, 湯浅 一哉, 大場 一郎

    日本物理学会講演概要集   53.2.3   745  1998年

    DOI CiNii

▼全件表示

Misc

▼全件表示

共同研究・競争的資金等の研究課題

  • 量子測定と量子制御: 量子情報技術から統計力学の基礎まで

    日本学術振興会  科学研究費助成事業 学術研究助成基金助成金 基盤研究(C) (一般) (No. 18K03470)

    研究期間:

    2018年04月
    -
    2023年03月
     

    湯浅 一哉

  • 量子観測で迫る統計力学の基礎と量子情報

    日本学術振興会  科学研究費助成事業 学術研究助成基金助成金 基盤研究(C) (一般) (No. 26400406)

    研究期間:

    2014年04月
    -
    2018年03月
     

    湯浅 一哉

  • 量子コヒーレンスと量子観測の織りなす物理

    文部科学省  科学研究費助成事業 科学研究費補助金 若手研究(B) (No. 21740294)

    研究期間:

    2009年04月
    -
    2013年03月
     

    湯浅 一哉

  • 量子コヒーレンス制御とその量子情報分野への応用

    文部科学省  科学研究費補助金 若手研究(B) (No. 18740250)

    研究期間:

    2006年04月
    -
    2007年03月
     

    湯浅 一哉

  • 積分核を活用した確率過程量子化法

    文部科学省  科学研究費補助金 特別研究員奨励費 (No. 6617)

    研究期間:

    1998年04月
    -
    2001年03月
     

    湯浅 一哉

講演・口頭発表等

  • 繰り返し測定による量子ビットチャンネルのパラメータの推定

    松原 輝王, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人 日本物理学会  

    発表年月: 2016年

    開催年月:
    2016年
     
     

     概要を見る

    <p>量子チャンネルのパラメータを推定する問題を議論する.通常は系を推定対象のチャンネルに通す実験を独立に多数回行って得られる測定データからパラメータを推定するが,本講演では測定ごとに系の状態をリセットすることなくチャンネルに通しては測定する作業を繰り返してデータを集めるスキームを,量子ビットチャンネルを題材に検討する.任意の初期状態から推定できる,データ間の相関の情報を利用することで推定精度を向上できるなどの特長があることを示す.</p>

  • 非平衡定常状態における量子ゆらぎ定理:可解モデルによる解析

    諸留 昇平, 門内 隆明, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人 日本物理学会  

    発表年月: 2016年

    開催年月:
    2016年
     
     

     概要を見る

    <p>近年,非平衡過程を記述する「ゆらぎ定理」が注目を集めている.この定理は通常,熱平衡状態にある系にする仕事に注目したものであるが,本研究では,非平衡定常状態にある量子系に操作をしてゆらぎ定理が成立しているかを議論する.この際,可解モデルを採用し厳密に解析する.その結果,熱平衡状態ではゆらぎ定理が成立していたが,非平衡定常状態では成立しないことがわかり,非平衡定常状態でも成立するような物理量を探った.</p>

  • 量子多重散乱効果による量子状態推定精度の向上

    鈴木 貴大, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人 日本物理学会  

    発表年月: 2016年

    開催年月:
    2016年
     
     

     概要を見る

    <p>量子干渉効果を利用することによって量子状態推定の精度を向上できることを示す.推定対象のスピンにプローブスピンを散乱させる1次元散乱実験を行って得られる散乱データを通じて対象スピンの量子状態を推定する.この際,推定対象のスピンの脇に補助壁を立てると,プローブスピンは対象スピンと補助壁との間で多重散乱される.この多重散乱によって生じる量子干渉効果によって対象スピンの量子状態の推定精度を向上できることを示す.</p>

  • 補助系とのエンタングルメントによる量子ビットチャンネルのパラメータの推定精度の向上

    田中 康就, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人 日本物理学会  

    発表年月: 2016年

    開催年月:
    2016年
     
     

     概要を見る

    <p>量子チャンネルに含まれるパラメータを推定する問題を議論する. 量子チャンネルに通すプローブ量子系とエンタングルさせる補助系を導入することで, 量子チャンネルのパラメータを推定する精度を向上する可能性を追究する.量子ビットチャンネルを題材に検討し, (i)推定対象のパラメータによってその方法が有用な場合とそうでない場合があること, (ii)有用な場合でも, 必ずしも最大エンタングル状態が最適とは限らないことを示す.</p>

  • 21pAN-3 光学位相シフトの量子計測に対する最適な多モードガウス型純粋状態

    松岡 耕司, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2015年

    開催年月:
    2015年
     
     
  • 24aAJ-6 孤立量子系における典型的な非平衡定常状態

    門内 隆明, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2015年

    開催年月:
    2015年
     
     
  • 17aCX-7 ミクロカノニカル状態におけるKMS条件と熱力学極限

    門内 隆明, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2015年

    開催年月:
    2015年
     
     
  • 9pAP-6 典型的純粋状態と量子測定による対称性の破れ(9pAP 非平衡定常系2,領域11(物性基礎論・統計力学・流体物理・応用数学・社会経済物理))

    門内 隆明, Iazzi Mauro, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2014年08月

    開催年月:
    2014年08月
     
     
  • 19aAK-10 同種粒子性を利用する量子計測と識別不可能性(19aAK 量子エレクトロニクス(量子測定),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    松岡 耕司, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2012年08月

    開催年月:
    2012年08月
     
     
  • 18aAK-5 マッハ・ツェンダー干渉計を用いて2量子ビット間に任意の初期状態から確率1でエンタングルメントを生成する方法(18aAK 量子エレクトロニクス(量子情報理論),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    稲葉 弘一, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2012年08月

    開催年月:
    2012年08月
     
     
  • 27pBE-2 エルゴード写像による量子パラメータ推定(27pBE 量子統計・量子情報,領域1(原子・分子,量子エレクトロニクス,放射線物理))

    安藤 慧, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2012年03月

    開催年月:
    2012年03月
     
     
  • 27pBE-3 複数の同種粒子の散乱によるポテンシャル強度の推定(27pBE 量子統計・量子情報,領域1(原子・分子,量子エレクトロニクス,放射線物理))

    奥出 淳也, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2012年03月

    開催年月:
    2012年03月
     
     
  • 22pEB-5 観測とランダム操作の繰り返しによる2量子ビット間エンタングルメント生成(22pEB 量子エレクトロニクス(量子測定・量子エレクトロニクス・分光),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    寺澤 翔一郎, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2011年08月

    開催年月:
    2011年08月
     
     
  • 23aRF-6 補助系に対する観測とフィードバックの繰り返しによる2量子ビット間エンタングルメント生成(23aRF 量子エレクトロニクス(量子情報基礎理論),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    奥出 淳也, 湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2010年08月

    開催年月:
    2010年08月
     
     
  • 25pRD-3 2つの独立な超伝導体から放出されるクーパー対の干渉(25pRD 量子エレクトロニクス(量エレ),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    湯浅 一哉, Iazzi Mauro

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2010年08月

    開催年月:
    2010年08月
     
     
  • 26pZE-10 媒介系の共鳴散乱の繰り返しによる2量子ビット間のエンタングルメント生成(量子エレクトロニクス(量子情報,量子測定,エンタングルメント,デコヒーレンス),領域1,原子・分子,量子エレクトロニクス,放射線物理)

    湯浅 一哉, 中里 弘道, Giovannetti Vittorio, Burgarth Daniel

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2009年08月

    開催年月:
    2009年08月
     
     
  • 27pSK-11 超伝導体から電界放出される電子対のエンタングルメント(27pSK 量子エレクトロニクス(輻射場の量子情報処理,エンタングルメント),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    湯浅 一哉, 大場 一郎, 田崎 秀一, 中里 弘道, Facchi Paolo, Fazio Rosario, Pascazio Saverio

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2009年03月

    開催年月:
    2009年03月
     
     
  • 20aZD-12 三次元散乱問題として捉えたエンタングルメント生成II(20aZD 量子エレクトロニクス(量子コンピュータ,量子情報,量子測定,エンタングルメント),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    湯浅 一哉, 肥田 雄一郎, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2008年08月

    開催年月:
    2008年08月
     
     
  • 26aWD-7 粒子源から放出されるビーム中の2粒子量子干渉の場の理論的取り扱い(量子カオス系・量子系一般,領域11,統計力学,物性基礎論,応用数学,力学,流体物理)

    湯浅 一哉, 大場 一郎, 田崎 秀一, 中里 弘道, ファッキ P., パスカッチオ S.

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2008年02月

    開催年月:
    2008年02月
     
     
  • 23pRG-4 三次元散乱問題として捉えたエンタングルメント生成(量子エレクトロニクス(量子情報),領域1,原子・分子,量子エレクトロニクス,放射線物理)

    肥田 雄一郎, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2007年08月

    開催年月:
    2007年08月
     
     
  • 18pWD-11 マスター方程式を演算子形式で解く方法(量子力学・量子カオス,領域11,原子・分子,量子エレクトロニクス,放射線物理)

    肥田 雄一郎, 中里 弘道, 湯浅 一哉, Militello B., Napoli A., Messina A.

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2007年02月

    開催年月:
    2007年02月
     
     
  • 25pRB-6 媒介系を用いたエンタングルメント生成におけるデコヒーレンスの影響(25pRB 量子エレクトロニクス(量子情報),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    肥田 雄一郎, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2006年08月

    開催年月:
    2006年08月
     
     
  • 30aXG-6 射影演算子法によるマスター方程式の導出と初期相関(30aXG 量子力学・量子カオス,領域11(統計力学,物性基礎論,応用数学,力学,流体物理))

    湯浅 一哉, 田崎 秀一, 中里 弘道, 大場 一郎, 木村 元, ファッキ パオロ, パスカッチオ サベリオ

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2006年03月

    開催年月:
    2006年03月
     
     
  • 21pXE-10 積分核を含むLangevin方程式に基づいた短時間スケーリング則による臨界指数の評価(古典スピン系一般・古典フラストレート系,領域11(統計力学,物性基礎論,応用数学,力学,流体物理))

    乙部 毅, 服部 望, 湯浅 一哉, 中里 弘道, 岡野 啓介

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2005年08月

    開催年月:
    2005年08月
     
     
  • 21pXE-9 積分核を含むLangevin方程式に基づく臨界緩和過程の短時間スケーリング則(古典スピン系一般・古典フラストレート系,領域11(統計力学,物性基礎論,応用数学,力学,流体物理))

    服部 望, 乙部 毅, 湯浅 一哉, 中里 弘道, 岡野 啓介

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2005年08月

    開催年月:
    2005年08月
     
     
  • 22pWA-7 端点1量子ビットの測定による多量子ビット系の状態推定(量子エレクトロニクス,領域1(原子・分子,量子エレクトロニクス,放射線物理))

    岡野 康介, 湯浅 一哉, 中里 弘道, 陽 完治

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2005年08月

    開催年月:
    2005年08月
     
     
  • 27aYE-4 離れた量子ビット間にエンタングル状態を効率良く抽出する方法(量子エレクトロニクス(量子情報),領域1(原子・分子,量子エレクトロニクス,放射線物理))

    湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2005年03月

    開催年月:
    2005年03月
     
     
  • 15pTF-10 ゼノン型観測による量子状態純化における観測エラーの影響(量子エレクトロニクス, 領域 1)

    岡野 康介, 鵜木 誠, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2004年08月

    開催年月:
    2004年08月
     
     
  • 28pXG-8 ゼノン型観測による量子状態の純粋化における測定時間間隔の揺らぎの影響(量子エレクトロニクス(量子情報理論))(領域1)

    鵜木 誠, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2004年03月

    開催年月:
    2004年03月
     
     
  • 23pTF-4 ゼノン型観測によるエンタングル状態の抽出

    中里 弘道, 湯浅 一哉, 鵜木 誠

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2003年08月

    開催年月:
    2003年08月
     
     
  • 31pSG-12 ゼノン型観測による量子状態の純粋化

    鵜木 誠, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2003年03月

    開催年月:
    2003年03月
     
     
  • 6aTA-5 中性子スピンを用いた量子ゼノン効果検証実験における測定効率の影響(その他の量子力学系,領域11)

    中黒 洋一, 鵜木 誠, 湯浅 一哉, 中里 弘道, Facchi P, Pascazio S

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2002年08月

    開催年月:
    2002年08月
     
     
  • 6pTA-6 量子ゼノン効果に及ぼす測定時間間隔の揺らぎの影響(その他の量子力学系,領域11)

    鵜木 誠, 中黒 洋一, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2002年08月

    開催年月:
    2002年08月
     
     
  • 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   一般社団法人日本物理学会  

    発表年月: 2002年03月

    開催年月:
    2002年03月
     
     
  • 24pXG-13 環境の影響下における量子ゼノン効果(24pXG 素粒子論,宇宙線, 領域1,領域11合同 量子論基礎,領域1(原子・分子,量子エレクトロニクス,放射線物理分野))

    湯浅 一哉, 中里 弘道, 高沢 智子

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2002年03月

    開催年月:
    2002年03月
     
     
  • 23aTE-4 速い確率極限近似

    湯浅 一哉, 木村 元, 今福 健太郎

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2000年09月

    開催年月:
    2000年09月
     
     
  • 30aSF-1 底なし系の確率過程量子化における積分核依存性

    湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2000年03月

    開催年月:
    2000年03月
     
     
  • 24aZB-4 Lindblad型マスター方程式を用いた確率共鳴現象の解析 II

    中村 桂一, 湯浅 一哉, 今福 健太郎, 大場 一郎

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 2000年03月

    開催年月:
    2000年03月
     
     
  • 25aSG-2 φ^3型底なし系の確率過程量量子化の試み

    杉山 弘晃, 湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1999年09月

    開催年月:
    1999年09月
     
     
  • 27aQ-11 微視的Hamiltonianに基づくLindblad演算子

    湯浅 一哉

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1999年09月

    開催年月:
    1999年09月
     
     
  • 27aQ-12 Lindblad型マスター方程式を用いた確率共鳴現象の解析

    中村 桂一, 湯浅 一哉, 今福 健太郎, 大場 一郎

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1999年09月

    開催年月:
    1999年09月
     
     
  • 31a-YD-9 底なし系の確率過程量子化に関するFokker-Planck方程式の解析解による解析

    湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1999年03月

    開催年月:
    1999年03月
     
     
  • 31a-XD-4 "古典的"と"量子論的(トンネル的)"遷移チャンネルをもつ系における確率共鳴現象

    今副 健太郎, 湯浅 一哉, 大場 一郎

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1999年03月

    開催年月:
    1999年03月
     
     
  • 5p-F-7 底なし系に対するFokker-Planck方程式の解析解の初期条件依存性

    湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1998年09月

    開催年月:
    1998年09月
     
     
  • 25p-H-5 スピン-ボソン系における確率共鳴現象について

    今福 健太郎, 湯浅 一哉, 大場 一郎

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1998年09月

    開催年月:
    1998年09月
     
     
  • 23p-C-10 確率過程量子化法によるクーロン・ポテンシャルに対する遷移確率振幅の計算

    湯浅 一哉, 中里 弘道

    日本物理学会講演概要集   一般社団法人日本物理学会  

    発表年月: 1997年09月

    開催年月:
    1997年09月
     
     
  • 9a-K-7 確率過程量子化法による遷移確率振幅の計算

    湯浅 一哉, 中里 弘道

    日本物理学会講演概要集. 秋の分科会   一般社団法人日本物理学会  

    発表年月: 1996年09月

    開催年月:
    1996年09月
     
     

▼全件表示

特定課題研究

  • 測定による量子制御: 量子情報技術から統計力学の基礎まで

    2018年  

     概要を見る

    ■光をプローブに利用する量子計測に関し,一般の多モード線形光学回路に含まれるパラメータをGauss型状態と呼ばれるクラスのプローブ光で計測する場合の計測精度限界を明らかにした.&nbsp;■未知のバックグラウンドパラメータが存在する状況における量子計測を議論し,バックグラウンドのみをプローブするプローブと主のプローブをエンタングルさせることによってバックグラウンドの影響を除去しつつ高精度の計測が可能になることを明らかにした.&nbsp;■Maxwellの悪魔によって電流を逆流させるモデルを解析し,逆流電流の大きさを悪魔が獲得する情報量,もしくは,悪魔の記憶消去に伴って放出されるエントロピーで評価する不等式を得た.

  • 量子系制御とその量子情報技術への応用

    2017年  

     概要を見る

    「量子系制御」をキーワードに量子情報技術に関わる話題,特に「観測による量子系制御」と「量子計測」に取り組み,次の成果を得た.■いかなる複雑なMarkov 過程も,互いに可換な時間発展生成子で駆動される自明な時間発展を測定で射影して得られるものとして理解できることを明らかにし,“Lindbladian Purification” を提唱した.■繰り返し測定によって系の時間発展を変化させつつデータを得る計測スキームを温度を計測する問題に適用し,その有用性を明らかにした.■最適制御の考え方を量子計測の問題に援用し,計測の過程で量子制御を加えることで計測制度を顕著に向上できることを明らかにした.

  • 観測による量子系制御と量子情報技術への展開

    2016年  

     概要を見る

    「量子観測」をキーワードに量子情報技術に関わる話題,特に「量子系制御」と「量子計測」に取り組み,次の成果を得た.■観測や緩和過程で量子系に対する制御性を向上させる可能性を追究し,緩和過程によってデコヒーレンスの影響を遮断しつつ完全可制御も達成できる興味深い例を提示した.この成果は論文誌の“Editors’ Suggestion”に選ばれた.■プローブと補助系とのエンタングルメントを利用する量子計測の可能性を検討し,必ずしもエンタングルメントが有用ではないことを明らかにした.■計測対象をリング干渉計に組み込むことでプローブ過程に生じる量子干渉効果によって計測精度を向上できることを明らかにした.

  • 量子観測をキーワードに追究する量子情報技術

    2015年  

     概要を見る

    「量子観測」をキーワードに,量子情報技術に関わる話題,特に「量子系制御」と「量子計測」の研究に取り組み,以下の成果を得た.■制御の最中に観測を加えると実行可能な制御の種類を増やせるが,逆にいかなる複雑な制御も単純な制御+量子観測の形に表現できることを指摘し,その一般論を構築して論文発表した.■最も一般的な2入力2出力線形光学回路に含まれるパラメータの量子計測精度限界を明らかにし,論文発表した.■系に立て続けに観測して得られるデータ列から計測対象の値を推定する方法を検討し,測定データ間に存在する相関の情報を活用することで精度の高い計測が可能になることを明らかにして論文発表した.

  • 量子観測をキーワードに迫る量子論の基礎と量子情報

    2013年  

     概要を見る

    本研究課題は,「量子観測」をキーワードに量子論の基礎的諸問題や量子情報技術に関わる問題に取り組むことを目的としていた.主に「量子コヒーレンス」,「量子系制御」,「量子計測」の 3つの柱を中心に,それらの話題において「量子観測」が非自明で意外な役割を演じる興味深いテーマに取り組み,以下の研究成果を得た.9ヶ月間ほどの研究期間ではあったが,4編の論文発表に結実した.■量子コヒーレンス 論文発表には至っていないが,(1) ボース凝縮体の干渉現象が量子論における観測に対する射影仮説を素直に適用する形で説明できることを解明した.さらに,このアプローチによって議論の見通しが良くなり,(2) 超伝導体間に流れるジョセフソン電流も全く同様に説明できることが明らかになりつつある.対称性が自発的に破れた状態が観測による射影によって実現されるという「観測による量子コヒーレンス」がフェルミ粒子系でも成立することを明確に示す最初の例になる.現在,論文執筆に向けて,細部の検討を継続している.■量子系制御 量子系に対して観測を行うとその観測対象の状態が乱されてしまう効果をうまく活用することによって量子系を制御しようという「観測による量子系制御」のアイデアを追究した.(1) その数学的基盤となる「量子エルゴード写像」に関する一連の数学的定理を詳細に検討し,論文としてまとめて発表した.(2)「観測による量子系制御」の可能性の 1つとして,量子系に観測を頻繁に行うことで生じる「量子ゼノン効果」を拡張した制御手法の可能性を検討した.通常の量子ゼノン効果の場合とは異なって,観測の仕方を徐々に変えていくと,量子系を断熱的に変化させたときに生じるのと同じ非自明な幾何学的位相を生じさせることができることを明らかにし,量子計算等の量子情報処理に必要となる量子演算ゲートを実現する一つの方法として論文発表した. ■量子計測 (1) 量子情報処理デバイスの実現を目指す量子ドット系において,そのデバイスが想定通りに機能するかどうかを調べる際に必要となる「量子プロセス推定」を実現する方法を検討し,論文発表した.(2) インプットーアウトプット関係からブラックボックス内のシステムを推定する「量子システム同定」の我々の理論を,現実には避けがたい開放系の時間発展をも含められる形に拡張することに成功し,論文発表した.

  • 量子観測で迫る量子論の基礎と量子情報

    2012年  

     概要を見る

    本研究課題の目的は,量子論の世界の不思議が際立つ「量子観測」をキーワードに,量子論の基礎と量子情報技術に関わるテーマに取り組んで,量子論の本質に迫り,量子性を活用する量子技術に寄与することにあった.量子論の本質が凝縮されている干渉現象を追究して「量子コヒーレンス」に対する理解を深め,「量子系制御」の独自のアイデアを発展させて量子情報技術に新たな手法を提供し,「量子計測」の話題への取り組みを通じて量子性の新たな可能性を見出すことをテーマに研究を展開して,以下の成果を得た.([…] は研究成果発表欄の研究業績に添えた番号を参照する.)■量子コヒーレンス1.フランソン干渉計を利用してクーパー電子対の 2電子間相関長や重心運動のド・ブロイ波長を計測できることを示した [6].2.量子状態の量子性 (非可換性) を,干渉計を組み合わせてとらえる方法を提案した [1,5].3.2つの大自由度量子系間の典型的エンタングルメントに見られる相転移を,エンタングルメントの指標としてエントロピーを採用して解析し,他の簡易的な指標の場合よりも相転移が滑らかになることを明らかにした [3].4.BCS状態にある2つの独立なフェルミ原子気体間の干渉を議論し,もともと位相相関の無い原子気体同士でも,原子気体を撮像する観測によって原子気体間の相対位相が確定し,コヒーレンスがもたらされることを示した [14].■量子系制御5.多重散乱の干渉効果を利用して書き込みと読み出しができる量子メモリを提案した [4].6.観測の繰り返しによる量子状態生成の独自の手法を支える量子写像のエルゴード性・混合性に関する数学的基礎を整備した [2].7.観測の繰り返しによる量子状態生成の独自の手法をマッハ・ツェンダー干渉計の設定に適用し,エンタングルメント生成のスキームを提案した [10,12].8.観測の繰り返しによる量子状態生成の独自の手法に対する環境系の影響を検討し,手順を工夫することでスキームを頑強にできることを示した [11].■量子計測9.多数回試行が想定される量子論にあって1回の試行で得られる観測データから系のパラメータを推定する方法を示した [8].10.同種粒子の識別不可能性に起因する多粒子干渉効果で計測精度を向上できることを示した [9,13].

  • 有限温度下における量子系のダイナミクス

    2003年  

     概要を見る

    通常,緩和過程というと,指数関数的緩和が観測されるが,不安定量子状態の崩壊過程を詳細に調べると,それは単純な指数関数則には従っていないことが明らかになる.こうした議論は,これまで主にゼロ温度の問題設定下で詳細に行われてきたが,本研究課題では,有限温度下をはじめとする様々な状況・問題設定で量子系の時間発展に関わる諸問題を議論することを目的としてきた.具体的に取り組んだ研究テーマとその成果は,以下の通りである.1. 量子散逸過程における指数関数的振舞いを手際よく抽出する手法であるvan Hove極限,及び,それを拡張した「確率極限」に関する研究を行った.特に,従来,弱い散逸がその適用対象であった確率極限を「強結合系」に適用する枠組みへと拡張し,その手法に基づいて,強結合下における散逸過程において緩和定数の温度依存性に対する「分岐現象」を発見した.2. 上述の非指数関数的振舞いの興味深い帰結として,「量子ゼノン効果」が知られている.これは,繰り返し行われる観測下において量子系の時間発展が抑制される効果であるが,その検証実験としてウィーンのRauchのグループが計画中の中性子スピンを用いた実験を議論し,現実には避けがたい「エラーが量子ゼノン効果に及ぼす影響」を評価するとともに,検証実験としての可能性を明らかにした.3. 量子ゼノン効果の場合と同様にして観測を繰り返すことで量子系を混合状態から純粋状態へと導く「量子状態純化」の新しい機構を発見した.その量子情報分野への応用を目指して「エンタングル状態」の純化,量子ビットの「初期化」の手法としての応用の可能性を示すとともに,その手法の様々なエラーに対する安定性を議論した.

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