Updated on 2024/02/27

写真a

 
TAKAHASHI, Junichi
 
Affiliation
Faculty of Science and Engineering, School of Fundamental Science and Engineering
Job title
Assistant Professor(non-tenure-track)
Degree
博士

Research Experience

  • 2022.10
    -
    Now

    Waseda University   School of Fundamental Science and Engineering

  • 2021.10
    -
    2022.09

    Kochi University   Research and Education Faculty Natural Sciences Cluster, Science and Technology Unit

  • 2018.04
    -
    2021.09

    Waseda University   Faculty of Science and Engineering

  • 2018.01
    -
    2018.03

    Waseda University   Research Institute for Science and Engineering

  • 2016.04
    -
    2017.12

    ソフトウエア開発会社   開発部

  • 2014.04
    -
    2016.03

    Waseda University   School of Fundamental Science and Engineering

  • 2013.04
    -
    2014.03

    Waseda University

▼display all

Education Background

  • 2013.04
    -
    2016.03

    Waseda University   Graduate School of Fundamental Science and Engineering  

  • 2011.04
    -
    2013.03

    Waseda University   Graduate School of Fundamental Science and Engineering  

  • 2007.04
    -
    2011.03

    Waseda University   School of Fundamental Science and Engineering  

Professional Memberships

  • 2022.10
    -
    Now

    日本数学会

  • 2021.08
    -
    Now

    日本キャリア開発協会

  • 2012.01
    -
    Now

    日本物理学会

Research Areas

  • Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics / Mathematical physics and fundamental theory of condensed matter physics
 

Papers

  • Rigged Hilbert space approach for non-Hermitian systems with positive definite metric

    S. Ohmori, J. Takahashi (co-first)

    Journal of Mathematical Physics   63 ( 12 ) 123503 - 123503  2022.12

     View Summary

    We investigate Dirac’s bra–ket formalism based on a rigged Hilbert space for a non-Hermitian quantum system with a positive-definite metric. First, the rigged Hilbert space, characterized by a positive-definite metric, is established. With the aid of the nuclear spectral theorem for the obtained rigged Hilbert space, spectral expansions are shown for the bra–kets by the generalized eigenvectors of a quasi-Hermitian operator. The spectral expansions are utilized to endow the complete bi-orthogonal system and the transformation theory between the Hermitian and non-Hermitian systems. As an example of application, we show a specific description of our rigged Hilbert space treatment for some parity-time symmetrical quantum systems.

    DOI

  • Dissipation-relaxation dynamics of a spin-1/2 particle with a Rashba-type spin-orbit coupling in an ohmic heat bath

    Tomohiro Hata, Eiji Nakano, Kei Iida, Hiroyuki Tajima, Junichi Takahashi

    Physical Review B   104 ( 14 )  2021.08

     View Summary

    Spin-orbit coupling (SOC), which is inherent to a Dirac particle that moves
    under the influence of electromagnetic fields, manifests itself in a variety of
    physical systems including non-relativistic ones. For instance, it plays an
    essential role in spintronics developed in the past few decades, particularly
    by controlling spin current generation and relaxation. In the present work, by
    using an extended Caldeira-Leggett model, we elucidate how the interplay
    between spin relaxation and momentum dissipation of an open system of a single
    spin-$1/2$ particle with a Rashba type SOC is induced by the interactions with
    a spinless, three-dimensional environment. Staring from the path integral
    formulation for the reduced density matrix of the system, we have derived a set
    of coupled nonlinear equations that consists of a quasi-classical Langevin
    equation for the momentum with a frictional term and a spin precession
    equation. The spin precesses around the effective magnetic field generated by
    both the SOC and the frictional term. It is found from analytical and numerical
    solutions to these equations that a spin torque effect included in the
    effective magnetic field causes a spin relaxation and that the spin and
    momentum orientations after a long time evolution are largely controlled by the
    Rashba coupling strength. Such a spin relaxation mechanism is qualitatively
    different from, e.g., the one encountered in semiconductors where essentially
    no momentum dissipation occurs due to the Pauli blocking.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Extracting non-local inter-polaron interactions from collisional dynamics

    Junichi Takahashi, Hiroyuki Tajima, Eiji Nakano, Kei Iida

    PHYSICAL REVIEW A   103 ( 4 )  2021.04

     View Summary

    This study develops a novel experimental method of deducing the profile of
    interaction induced between impurities in a trapped gas of ultracold Fermi/Bose
    atoms, which are often referred to as Fermi/Bose polarons. In this method, we
    consider a two-body Fermi/Bose polaron collision experiment in which impurities
    and atoms interact only weakly. Numerical simulations of the quantum dynamics
    reveal the possibility to obtain information regarding the non-local induced
    interaction between two polarons from a measured profile of the polaron wave
    packet at several snapshots. This is because the potential of the induced
    interaction is well balanced by the quantum potential whenever the WKB
    approximation for the relevant Schr\"{o}dinger equation is applicable.

    DOI

    Scopus

  • Polaron Problems in Ultracold Atoms: Role of a Fermi Sea across Different Spatial Dimensions and Quantum Fluctuations of a Bose Medium

    Hiroyuki Tajima, Junichi Takahashi, Simeon I. Mistakidis, Eiji Nakano, Kei Iida

    ATOMS   9 ( 1 )  2021.01

     View Summary

    The notion of a polaron, originally introduced in the context of electrons in
    ionic lattices, helps us to understand how a quantum impurity behaves when
    being immersed in and interacting with a many-body background. We discuss the
    impact of the impurities on the medium particles by considering feedback
    effects from polarons that can be realized in ultracold quantum gas
    experiments. In particular, we exemplify the modifications of the medium in the
    presence of either Fermi or Bose polarons. Regarding Fermi polarons we present
    a corresponding many-body diagrammatic approach operating at finite
    temperatures and discuss how mediated two- and three-body interactions are
    implemented within this framework. Utilizing this approach, we analyze the
    behavior of the spectral function of Fermi polarons at finite temperature by
    varying impurity-medium interactions as well as spatial dimensions from three
    to one. Interestingly, we reveal that the spectral function of the medium atoms
    could be a useful quantity for analyzing the transition/crossover from
    attractive polarons to molecules in three-dimensions. As for the Bose polaron,
    we showcase the depletion of the background Bose-Einstein condensate in the
    vicinity of the impurity atom. Such spatial modulations would be important for
    future investigations regarding the quantification of interpolaron correlations
    in Bose polaron problems.

    DOI

    Scopus

    15
    Citation
    (Scopus)
  • Semiclassical Analysis of Driven-Dissipative Excitonic Condensation

    R. Imai, J. Takahashi, T. Oyama, Y. Yamanaka

    PROCEEDINGS OF THE 14TH ASIA-PACIFIC PHYSICS CONFERENCE   2319  2021

     View Summary

    A theoretical study of excitonic condensation in a driven-dissipative semiconductor is presented. The system that we analyze is driven by a coherent light that creates electron-hole pairs and also includes the process of the annihilation of the pairs. To study the steady state realized in this nonequilibrium system. we employ the Schwinger-Keldysh path integral formalism, which is useful for discussing the semiclassical aspect. We derive an effective theory for the excitonic condensation in the driven-dissipative situation and present a condition on the amplitude and phase of the condensate.

    DOI

    Scopus

  • Quantum fluctuations of zero-modes for trapped two-component Bose-Einstein condensates

    Junichi Takahashi, Yuto Hayaki, Yoshiya Yamanaka

    PROCEEDINGS OF THE 14TH ASIA-PACIFIC PHYSICS CONFERENCE   2319  2021

     View Summary

    Zero-mode operators associated with a spontaneous breakdown of internal symmetry are often suppressed and their quantum fluctuations are neglected owing to the absence of a definite criterion for determining the ground state and infrared divergences in physical quantities. Because the zero-mode fluctuations for systems with finite-size and spatially inhomogeneity cannot be neglected, we have proposed a novel treatment of the zero-mode for finite systems, which helps determine the unique ground state and evaluate the physical quantities without divergence. Following the proposed treatment, we consider trapped systems with two-component Bose-Einstein condensates. The results obtained demonstrate that the interaction strength between the two components considerably affect the dynamical properties, illustrating the importance of the zero-mode for finite systems.

    DOI

    Scopus

  • Bose-Einstein condensation of dilute alpha clusters above four $α$ threshold in $^{16}$O in field theoretical superfluid cluster model

    Junichi Takahashi, Yoshiya Yamanaka, Shigeru Ohkubo

       2020.09

     View Summary

    Observed well-developed $\alpha$ cluster states in $^{16}$O, located above
    the four $\alpha$ threshold, are investigated from the viewpoint of
    Bose-Einstein condensation of $\alpha$ clusters by using a field-theoretical
    superfluid cluster model in which the order parameter is defined. The
    experimental energy levels are reproduced well for the first time by
    calculation. In particular, the observed 16.7 MeV $0_7^+$ and 18.8 MeV $0_8^+$
    states with low-excitation energies from the threshold are found to be
    understood as a manifestation of the states of the Nambu-Goldstone zero-mode
    operators, associated with the spontaneous symmetry breaking of the global
    phase, which is caused by the Bose-Einstein condensation of the vacuum 15.1 MeV
    $0^+_6$ state with a dilute well-developed $\alpha$ cluster structure just
    above the threshold. This gives evidence of the existence of the Bose-Einstein
    condensate of $\alpha$ clusters in $^{16}$O. It is found that the emergence of
    the energy level structure with a well-developed $\alpha$ cluster structure
    above the threshold is robust, almost independently of the condensation rate of
    $\alpha$ clusters under significant condensation rate. The finding of the
    mechanism why the level structure that is similar to $^{12}$C emerges above the
    four $\alpha$ threshold in $^{16}$O reinforces the concept of Bose-Einstein
    condensation of $\alpha$ clusters in addition to $^{12}$C.

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Supersolidity of the α cluster structure in the nucleus 12C

    S. Ohkubo, J. Takahashi, Y. Yamanaka

    Progress of Theoretical and Experimental Physics   2020 ( 4 ) 1 - 11  2020.04  [Refereed]

  • Collisional dynamics of polaronic clouds immersed in a Fermi sea

    Hiroyuki Tajima, Junichi Takahashi, Eiji Nakano, Kei Iida

    PHYSICAL REVIEW A   102 ( 5 )  2019.12

     View Summary

    We propose a new protocol to examine many-polaron properties in a cold atom
    experiment. Initially, polaronic clouds are prepared around the opposite edges
    of a majority gas cloud. After time evolution, the collision of two clouds
    exhibits various polaronic effects. To see how {\it collective} properties of
    many polarons with mediated interactions appear in the case in which the
    impurity and majority gases are composed of mass-balanced fermions with
    different spin components, we perform a nonlinear hydrodynamic simulation for
    collisional dynamics of two Fermi polaronic clouds. We found that the dynamics
    is governed by the impurity Fermi pressure, polaron energy, and multi-polaron
    correlations. In particular, shock waves occur in such a way as to reflect the
    many-body properties of polarons through the first sound of minority clouds.
    Our idea is applicable to other systems such as Bose polarons as well as
    mass-imbalanced mixtures.

    DOI

    Scopus

    8
    Citation
    (Scopus)
  • Bose polaron in spherical trap potentials: Spatial structure and quantum depletion

    Junichi Takahashi, Ryosuke Imai, Eiji Nakano, Kei Iida

    Physical Review A   100 ( 2 )  2019.04

     View Summary

    We investigate how the presence of a localized impurity in a Bose-Einstein
    condensate of trapped cold atoms that interact with each other weakly and
    repulsively affects the profile of the condensed and excited components at zero
    temperature. By solving the Gross-Pitaevskii and Bogoliubov-de Gennes
    equations, we find that an impurity-boson contact attraction (repulsion) causes
    both components to change in spatial structure in such a way as to be enhanced
    (suppressed) around the impurity, while slightly declining (growing) in a far
    region from the impurity. Such behavior of the quantum depletion of the
    condensate can be understood by decomposing the impurity-induced change in the
    profile of the excited component with respect to the radial and azimuthal
    quantum number. A significant role of the centrifugal potential and the "hole"
    excitation level is thus clarified.

    DOI

    Scopus

    11
    Citation
    (Scopus)
  • New description to soft modes in N-alpha cluster states as Bose-Einstein condensation based on quantum field theory with zero mode excitation

    J. Takahashi, R. Katsuragi, Y. Kazama, Y. Nakamura, Y. Yamanaka, S. Ohkubo

    AIP Conference Proceedings   2038   020024  2018.11  [Refereed]

    DOI

    Scopus

  • Bose-Einstein condensation of α clusters and new soft mode in 12C–52Fe 4N nuclei in a field-theoretical superfluid cluster model

    R. Katsuragi, Y. Kazama, J. Takahashi, Y. Nakamura, Y. Yamanaka, S. Ohkubo

    Physical Review C   98 ( 4 ) 044303  2018.10  [Refereed]

     View Summary

    Bose–Einstein condensation of α clusters in light and medium-heavy nuclei is studied in the frame of the field-theoretical superfluid cluster model. The order parameter of the phase transition from the Wigner phase to the Nambu–Goldstone phase is a superfluid amplitude, square of the moduli of which is the superfluid density distribution. The zero-mode operators due to the spontaneous symmetry breaking of the global phase in the finite number of α clusters are rigorously treated. The theory is systematically applied to Nα nuclei from 12C to 52Fe at various condensation rates. In 12C it is found that the energy levels of the gas-like well-developed α cluster states above the Hoyle state are reproduced well in agreement with experiment for realistic condensation rates of α clusters. The electric E2 and E0 transitions are calculated and found to be sensitive to the condensation rates. The profound raison d'être of the α cluster gas-like states above the Hoyle state, whose structure has been interpreted geometrically in the nuclear models without the order parameter such as the cluster models or ab initio calculations, is revealed. It is found that, in addition to the Bogoliubov–de Gennes vibrational mode states, collective states of the zero-mode operators appear systematically at low excitation energies from the Nα
    threshold energy. These collective states, which are new-type soft modes in nuclei due to the Bose–Einstein condensation of the α clusters, emerge systematically in light– and medium-heavy–mass regions and are also located at high excitation energies from the ground state in contrast to the traditional concept of soft mode in the low-excitation-energy region.

    DOI

    Scopus

    10
    Citation
    (Scopus)
  • Effective field theory of Bose-Einstein condensation of α clusters and Nambu-Goldstone-Higgs states in C 12

    Nakamura, Y, Nakamura, Y, Takahashi, J, Takahashi, J, Yamanaka, Y, Ohkubo, S, Ohkubo, S

    Physical Review C - Nuclear Physics   94 ( 1 ) 014314 (8 pages)  2016.07  [Refereed]

     View Summary

    © 2016 American Physical Society.An effective field theory of α-cluster condensation is formulated as a spontaneously broken symmetry in quantum field theory to understand the raison d'être and the nature of the Hoyle and α-cluster states in C12. The Nambu-Goldstone and Higgs mode operators in infinite systems are replaced with a pair of canonical operators whose Hamiltonian gives rise to discrete energy states in addition to the Bogoliubov-de Gennes excited states. The calculations reproduce well the experimental spectrum of the α-cluster states. The existence of the Nambu-Goldstone-Higgs states is demonstrated and crucial. The γ-decay transitions are also obtained.

    DOI

    Scopus

    14
    Citation
    (Scopus)
  • Effective field theory of Bose-Einstein condensation of a clusters and Nambu-Goldstone-Higgs states in C-12

    Y. Nakamura, J. Takahashi, Y. Yamanaka, S. Ohkubo

    PHYSICAL REVIEW C   94 ( 1 ) 014314  2016.07  [Refereed]

     View Summary

    An effective field theory of alpha-cluster condensation is formulated as a spontaneously broken symmetry in quantum field theory to understand the raison d'etre and the nature of the Hoyle and alpha-cluster states in C-12. The Nambu-Goldstone and Higgs mode operators in infinite systems are replaced with a pair of canonical operators whose Hamiltonian gives rise to discrete energy states in addition to the Bogoliubov-de Gennes excited states. The calculations reproduce well the experimental spectrum of the alpha-cluster states. The existence of the Nambu-Goldstone-Higgs states is demonstrated and crucial. The gamma-decay transitions are also obtained.

    DOI J-GLOBAL

    Scopus

    14
    Citation
    (Scopus)
  • Interacting multiple zero mode formulation and its application to a system consisting of a dark soliton in a condensate

    J. Takahashi, Y. Nakamura, Y. Yamanaka

    PHYSICAL REVIEW A   92 ( 2 )  2015.08  [Refereed]

     View Summary

    To formulate the zero modes in a finite-size system with spontaneous breakdown of symmetries in quantum field theory is not trivial, for in the naive Bogoliubov theory, one encounters difficulties such as phase diffusion, the absence of a definite criterion for determining the ground state, and infrared divergences. An interacting zero mode formulation that has been proposed for systems with a single zero mode to avoid these difficulties is extended to general systems with multiple zero modes. It naturally and definitely gives the interactions among the quantized zero modes, the consequences of which can be observed experimentally. In this paper, as a typical example, we consider an atomic Bose-Einstein condensed system with a dark soliton that contains two zero modes corresponding to the spontaneous breakdown of the U(1) gauge and translational symmetries. Then we evaluate the standard deviations of the zero mode operators and see how the mutual interaction between the two zero modes affects them.

    DOI

    Scopus

    3
    Citation
    (Scopus)
  • Dynamical instability induced by the zero mode under symmetry breaking external perturbation

    J. Takahashi, Y. Nakamura, Y. Yamanaka

    ANNALS OF PHYSICS   347   250 - 260  2014.08  [Refereed]

     View Summary

    A complex eigenvalue in the Bogoliubov-de Gennes equations for a stationary Bose-Einstein condensate in the ultracold atomic system indicates the dynamical instability of the system. We also have the modes with zero eigenvalues for the condensate, called the zero modes, which originate from the spontaneous breakdown of symmetries. Although the zero modes are suppressed in many theoretical analyses, we take account of them in this paper and argue that a zero mode can change into one with a pure imaginary eigenvalue by applying a symmetry breaking external perturbation potential. This emergence of a pure imaginary mode adds a new type of scenario of dynamical instability to that characterized by the complex eigenvalue of the usual excitation modes. For illustration, we deal with two one-dimensional homogeneous Bose-Einstein condensate systems with a single dark soliton under a respective perturbation potential, breaking the invariance under translation, to derive pure imaginary modes. (C) 2014 Elsevier Inc. All rights reserved.

    DOI

    Scopus

    3
    Citation
    (Scopus)
  • Formulation for the zero mode of a Bose-Einstein condensate beyond the Bogoliubov approximation

    Y. Nakamura, J. Takahashi, Y. Yamanaka

    PHYSICAL REVIEW A   89 ( 1 ) 013613  2014.01  [Refereed]

     View Summary

    The unperturbed Hamiltonian for the Bose-Einstein condensate, which includes not only the first and second powers of the zero mode operators but also the higher ones, is proposed to determine a unique and stationary vacuum at zero temperature. From the standpoint of quantum field theory, it is done in a consistent manner that the canonical commutation relation of the field operator is kept. In this formulation, the condensate phase does not diffuse and is robust against the quantum fluctuation of the zero mode. The standard deviation for the phase operator depends on the condensed atom number with the exponent of -1/3, which is universal for both homogeneous and inhomogeneous systems.

    DOI

    Scopus

    14
    Citation
    (Scopus)
  • ダークソリトンのある冷却原子系におけるゼロモードの役割

    高橋淳一

    物性研究・電子版   2 ( 3 ) [1]  2013.08  [Refereed]

    DOI CiNii

  • Relationship Between Dynamical Instability and Zero Modes for Dark Soliton in Bose–Einstein Condensate

    J. Takahashi, Y. Nakamura, Y. Yamanaka

    JPS Conference Proceedings   1   012100  2013.07  [Refereed]

     View Summary

    Investigating the Bogoliubov–de Gennes equation, widely used in the analysis of Bose–Einstein condensate in neutral atomic gases, we reveal some aspect of the interplay between the zero and complex modes. The complex mode implies that the system is dynamically unstable. The zero modes originate from the spontaneous symmetry breakdown, but their roles are not clear because they cause the infrared divergence. In this paper, we deal with the system of a dark soliton in Bose–Einstein condensate which has two zero modes corresponding to the spontaneously broken U(1) gauge and translational symmetries, and show that the zero and its adjoint modes, associated with the spontaneous breakdown of translational symmetry, turn into pure imaginary modes under theperturbation which explicitly breaks translational symmetry.

    DOI

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Presentations

  • ゼロモード由来の量子揺らぎがBose-Einstein凝縮系に与える影響

    高橋淳一, 山中由也

    QUAntum Theory & Technology Un-Official Meeting 

    Presentation date: 2018.10

  • 冷却フェルミ原子系における対凝縮と有限サイズ効果

    高橋淳一, 山中由也

    熱場の量子論とその応用2018 

    Presentation date: 2018.08

  • Pair condensation theory for systems of trapped cold fermionic atoms

    J. Takahashi, Y. Yamanaka

    26th International Conference on Atomic Physics  (Barcelona) 

    Presentation date: 2018.07

  • New description to soft modes in N-alpha cluster states as Bose-Einstein condensation based on quantum field theory with zero mode excitation

    Junichi Takahashi, R. Katsuragi, Y. Kazama, Y. Nakamura, Y. Yamanaka, S. Ohkubo

    State of the Art in Nuclear Cluster Physics  (Galveston, Texas) 

    Presentation date: 2018.05

  • Collective modes of chiral superfuids in Bose-Bose mixtures in optical lattices

    Junichi Takahashi, Ippei Danshita

    Presentation date: 2016.03

  • Interacting multiple zero mode formulation for a dark soliton in a Bose-Einstein condensate

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    APS march meeting  (Baltimore) 

    Presentation date: 2016.03

  • Quantum fluctuation of zero modes for the depletion of the dark soliton

    Takuma Kawaguchi, Yusuke Nakamura, Junichi Takahashi, Yoshiya Yamanaka

    Presentation date: 2015.09

  • Dynamical instability induced by zero mode in cold atomic system

    Junichi Takahashi  [Invited]

    (Kyoto) 

    Presentation date: 2015.08

  • Zero modes and their quantum state for gray soliton in cold atomic gas

    Yusuke Nakamura, Takuma Kawaguchi, Junichi Takahashi, Yoshiya Yamanaka

    Presentation date: 2015.03

  • Quantum state of soliton and its depletion

    J. Takahashi, Y. Nakamura, Y. Yamanaka

    Presentation date: 2015.03

  • Bose-Einstein凝縮体に対するゼロモード量子状態と原子核におけるアルファ凝縮模型への応用

    中村祐介, 高橋淳一, 山中由也, 大久保茂男

    熱場の量子論とその応用 

    Presentation date: 2014.09

  • Analysis on zero mode and phase fluctuation for Bese −Einstein condensate of confined cold atomic gas

    Yusuke Nakamura, Junichi Takahashi, Yoshiya Yamanaka

    Presentation date: 2014.09

  • 8aAW-12 Analysis on zero mode and phase fluctuation for Bose-Einstein condensate of confined cold atomic gas

    Nakamura Yusuke, Takahashi Junichi, Yamanaka Yoshiya

    Meeting abstracts of the Physical Society of Japan  The Physical Society of Japan (JPS)

    Presentation date: 2014.08

    Event date:
    2014.08
     
     
  • Quantum state for zero mode of cold atomic gas system with Bose-Einstein condensate

    Yusuke Nakamura, Junichi Takahashi, Yoshiya Yamanaka

    24th International Conference on Atomic Physics  (Washington D.C.) 

    Presentation date: 2014.08

  • Quantum fluctuation of soliton in Bose-Einstein condensate beyond Bogoliubov approximation

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    24th International Conference on Atomic Physics  (Washington, D.C.) 

    Presentation date: 2014.08

  • Quantum state for Nambu-Goldstone mode of Bose-Einstein condensate

    Yusuke Nakamura, Junichi Takahashi, Yoshiya Yamanaka

    Higgs Mode in Condensed Matter and Quantum Gases  (Kyoto) 

    Presentation date: 2014.06

  • Nambu-Goldstone mode associated with a soliton and its dynamics, Higgs Mode in Condensed Matter and Quantum Gases

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    Higgs Mode in Condensed Matter and Quantum Gases  (Kyoto) 

    Presentation date: 2014.06

  • 27aCF-6 Relation between snake instability and zero mode of translational invariance for two-dimensional system with soliton

    Takahashi Junichi, Nakamura Yusuke, Yamanaka Yoshiya

    Meeting abstracts of the Physical Society of Japan  The Physical Society of Japan (JPS)

    Presentation date: 2014.03

    Event date:
    2014.03
     
     
  • Relations between dynamical instability and zero modes for dark soliton in Bose-Einstein condensate

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    Presentation date: 2013.09

  • Relations between dynamical instability and zero modes for dark soliton in Bose-Einstein condensate

    Takahashi Junichi, Nakamura Yusuke, Yamanaka Yoshiya

    Meeting abstracts of the Physical Society of Japan  The Physical Society of Japan (JPS)

    Presentation date: 2013.08

    Event date:
    2013.08
     
     
  • Relationship between dynamical instability and zero modes for dark soliton in Bose-Einstein condensate

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    The 12th Asia Pacific Physics Conference  (Chiba) 

    Presentation date: 2013.07

  • 28pEE-6 Analysis on Bogoliubov-de Gennes method and Ward-Takahashi identity for Bose-Einstein condensates of trapped neutral atomic gases

    Takahashi Junichi, Nakamura Yusuke, Yamanaka Yoshiya

    Meeting abstracts of the Physical Society of Japan  The Physical Society of Japan (JPS)

    Presentation date: 2013.03

    Event date:
    2013.03
     
     
  • Analysis on Bogoliubov-de Gennes method and Ward-Takahashi identity for Bose-Einstein condensates of trapped neutral atomic gases

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    Presentation date: 2013.03

  • 捕捉されたBose-Einstein凝縮系におけるBogoliubov de-Gennesの方法とゼロモード

    高橋淳一, 中村祐介, 山中由也

    2012年熱場の量子論とその応用 

    Presentation date: 2012.09

  • The roles of the two zero and adjoint modes in the dynamics of dark soliton

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    Presentation date: 2012.09

  • 19aPSB-27 The roles of the two zero and adjoint modes in the dynamics of dark soliton

    Takahashi Junichi, Nakamura Yusuke, Yamanaka Yoshiya

    Meeting abstracts of the Physical Society of Japan  The Physical Society of Japan (JPS)

    Presentation date: 2012.08

    Event date:
    2012.08
     
     
  • 捕捉されたBose-Einstein凝縮系におけるBogoliubov de-Gennesの方法とzero modeの役割

    高橋淳一

    第57回物性若手夏の学校 

    Presentation date: 2012.08

  • The roles of the two zero and adjoint modes in the dynamics of dark soliton

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

    23rd International Conference on Atomic Physics  (Paris) 

    Presentation date: 2012.07

  • Relation between snake instability and zero mode of transnational invariance for two-dimensional system with soliton

    Junichi Takahashi, Yusuke Nakamura, Yoshiya Yamanaka

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Research Projects

  • Construction of triplet spaces for modern quantum theory

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

    Project Year :

    2022.04
    -
    2025.03
     

  • 固体デバイスを想定した量子リザバーコンピューティングにおける画像判定精度の検証

    キオクシア若手奨励研究

    Project Year :

    2023.07
    -
    2024.02
     

  • Analysis for inhomogeneous Bose-Einstein condensate system including quantum fluctuation of zero-mode

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

    Project Year :

    2019.04
    -
    2022.03
     

    Takahashi Junichi

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    The purpose of this study is to elucidate the physical phenomenon in which the quantum fluctuation of zero mode is important. During the research period, we have conducted research on zero-mode quantum fluctuations for the two-component Bose-Einstein condensation, the polaron realized by the cold atomic systems, the alpha condensation state of the nucleus, and the driven-dissipative excitonic condensation. We have shown that the two-component condensed system and the alpha condensed system are promising systems in which zero-mode quantum fluctuations appear prominently during this study period. We also succeeded in deriving the basic equations that form the basis for analyzing zero-mode quantum fluctuations for polaron and driven-dissipative condensates.

  • Rigged Hilbert空間論を用いた非エルミート量子力学の数学的基礎付け

    笹川科学研究助成

    Project Year :

    2021.04
    -
    2022.02
     

  • Formulation of quantum fluctuation of zero mode in inhomogeneous systems and its applications to cold atomic systems and nuclei

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Project Year :

    2016.04
    -
    2019.03
     

    Yamanaka Yoshiya, OHKUBO Shigeo, NAKAMURA Yuusuke, KUWAHARA Yukiro, TAKAHASHI Junichi, IMAI Ryousuke, KAWAGUCHI Takuma, TORII Yuusaku, OYAMA Takahiro, KATSURAGI Rei, KAZAMA Yuuki, HAYAKI Yuuto

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    The zero mode associated with a spontaneous breakdown of a continuous symmetry plays a crucial role.Its quantum fluctuations have not been taken account of explicitly for infinite homogeneous systems.But it is not the case for finite inhomogeneous systems, for which a new consistent formulation to include zero mode fluctuations explicitly has been proposed recently. In this study, we apply it to cold stomic systems and nuclear systems descibed by the alpha cluster model, and to analyze physical effects of quantum fluctuations of the zero modes qunatitatively. The results can be tested experimentally.

  • Quantum transport equation snd its application to ultracold atomic system

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

    Project Year :

    2013.04
    -
    2016.03
     

    YAMANAKA Yoshiya, NAKAMAURA Yuusuke, INOUE Motoyoshi, KUWAHARA Yukiro, TAKAHASHI Junichi

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    We derived the quantum transport equations for ultracold atomic systems without condensate from the formulation of nonequilibrium processes based on quantum field theory, and solved them numerically. It is shown that the imaginary part in the self-energy is essential for relaxation of the system to equilibrium, and that the non-Markoffian property decelerate nonequilibrium processes.In order to describe a nonequilibrium process involving condensation, we have established a new formulation of zero modes associated with a spontaneous breakdown of symmetry for a finite-size systems, for which the conventional Bogoliubov approximation is legitimate. The new formulation is applied to a system of a dark soliton in a condensate, or to the alpha-cluster model in nuclear physics, giving us new interpretations of the phenomena

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Syllabus

Teaching Experience

  • Experiment C in Electronic physical systems

    Waseda University  

    2022.10
    -
    Now
     

  • Advanced Topics on Quantum Physics

    Kochi University  

    2021.10
    -
    Now
     

  • Experiment of Physics

    Shibaura Institute of Technology  

    2023.10
    -
     
     

  • 理工学基礎実験2A

    早稲田大学  

  • 理工学基礎実験1B

    早稲田大学  

  • 理工学基礎実験1A

    早稲田大学  

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Internal Special Research Projects

  • Rigged Hilbert空間を⽤いた準束縛系の数学的基礎付け

    2021   大森 祥輔

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    準束縛状態を扱う土俵として、非エルミート量子系の数学的基礎の構築を試みた。本年度前半では、非エルミート系の中でも特別な対称性を持つクラスである準エルミート系についてrigged Hilbert空間の構築、及び、準エルミートな自己共役作用素に対する核スペクトル定理の証明を行った。詳細化が必要な箇所はいくつか残るものの、概ね証明は終了している。核スペクトル定理はrigged Hilbert空間に属する作用素の固有状態が完全であることを示すrigged Hilbert空間論の根底をなす定理であり、この部分が証明できたということは本研究としては非常に大きな一歩である。

  • ボーズ・ポーラロン系における不純物自己束縛相図

    2020  

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    本年度の研究では、当初の予定とは異なり、ポーラロン間の相互作用について研究を行った (arXiv:2011.07911)。その理由は、現実的な系において単一ポーラロンは未だに実現しておらず、不純物としては複数の原子を想定したほうが良いと判断したためである。そのため、当初は想定していなかったポーラロン間の相互作用について研究を行う必要が出てきた。ポーラロン間の相互作用として幾つかの関数型が理論的に提案されている。しかしながら、実験においてこれを直接観測した例はない。そこで、本研究では、実験において相互作用を直接観測する方法を提案した。また、ゼロモードに関係する研究として、16Oの励起スペクトルに関する研究も行った。 

  • 非一様凝縮系におけるゼロモード励起エネルギーと秩序変数に対する量子揺らぎの解析

    2018   早稲田大学基幹理工学部, 大阪大学核物理研究センター

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    申請者は自発的対称性の破れに伴い現れるゼロモード(南部-Goldstoneモード)が起源となる、秩序変数に対する量子揺らぎの解析を行った。秩序変数の量子揺らぎは凝縮粒子数が多くなる場合、無視されることがほとんどである。今回の研究では数個の粒子が凝縮しているとされる原子核中のαクラスター状態に対して秩序変数に対する量子揺らぎの効果を評価した。本解析では一般的なNα原子系に対して定性的な解析を行い、その後、定量的な解析を16^Oに対して行った。また、冷却原子系を想定した2成分Bose-Einstein凝縮系に対する応用についても研究を行った。

  • Bose-Einstein凝縮系におけるゼロモードが及ぼす物理的影響に関する研究

    2014   中村祐介, 山中由也, 大久保茂男

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    申請者は自発的対称性の破れに伴い現れるゼロモード(南部-Goldstoneモード)が物理量に与える影響の解析を行った。ゼロモードは自発的対称性が破れた系を特徴づける重要なモードであるが、ゼロモードを物理量の計算に取り入れることはほとんどの研究でされていなかった。今回の研究では冷却原子Bose-Einstein凝縮系を想定した模型において様々な物理量の評価を行った。本研究期間において申請者は、(a)ゼロモードがソリトンの動的・熱力学的不安定性に与える影響、(b)ゼロモードがソリトンの粒子分布に与える影響、(c)ゼロモードが原子核の励起モードに及ぼす影響、の3点を明らかにした。