Updated on 2025/06/23

写真a

 
YAMANAKA, Yoshiya
 
Affiliation
Faculty of Science and Engineering
Job title
Professor Emeritus
Degree
博士(理学) ( 早稲田大学 )
Doctor of Science ( Waseda University (Japan) )

Research Experience

  • 2007
    -
    Now

    早稲田大学基幹理工学部電子光システム学科(2015年より電子物理システム学科に改称)   教授

  • 2003
    -
    2007

    早稲田大学理工学部物質開発工学科   教授

  • 1993
    -
    2003

    早稲田大学大学院理工学研究科及び理工学部   非常勤講師

  • 1992
    -
    2003

    早稲田大学高等学院   教諭

  • 1986
    -
    1992

    カナダ・アルバータ大学物理教室   研究員、客員研究員、助手

  • 1985
    -
     

    早稲田大学理工学部   非常勤講師

  • 1985
    -
     

    日本学術振興会   昭和60年度奨励研究員

  • 1984
    -
     

    学習院大学理学部物理教室   助手

  • 1983
    -
     

    素粒子奨学会   昭和58年度奨励研究生

  • 1982
    -
     

    早稲田大学理工学研究所   昭和57年度奨励研究生

▼display all

Education Background

  • 1982.03
    -
     

    早稲田大学 学位(理学博士) 取得  

  • 1978
    -
    1982

    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 博士後期課程  

  • 1978
    -
     

    文部省高エネルギー物理学研究所理論部 受託学生  

  • 1978
    -
     

    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 博士前期課程 修了  

  • 1976
    -
     

    早稲田大学理工学部物理学科 卒業  

Committee Memberships

  • 2020
    -
     

    公益財団法人伊藤科学振興会  評議員

Professional Memberships

  •  
     
     

    Japan Physical Society of Japan

Research Areas

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

Research Interests

  • Quantum Field Theory, Thermal Field Theory, Particles Physics,Nuclear Physics, Cold Atoms, Stochastic QuantizationPhysics

 

Papers

  • 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 the four-α threshold in 16O in the field theoretical superfluid cluster model

    J Takahashi, Y Yamanaka, S Ohkubo

    Progress of Theoretical and Experimental Physics   2020 ( 9 ) 093D03/1 - 12  2020.09  [Refereed]  [International journal]

    DOI

    Scopus

    3
    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]

  • Dynamical properties of the finite-size Dicke model coupled to a thermal reservoir

    R. Imai, Y. Yamanaka

    J. Phys. Soc. Jpn.   88   024401-1 - 024401-7  2019.01  [Refereed]

    DOI

    Scopus

    2
    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

  • Stability of symmetry breaking states in finite-size Dicke model with photon leakage

    R. Imai, Y. Yamanaka

    Phys. Lett. A   382   3333 - 3338  2018.11  [Refereed]

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Bose--Einstein condensation of alpha clusters and new soft mode in 12C-52Fe 4N nuclei in field theoretical superfluid cluster model

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

    Phys. Rev. C   98   044303 (18pages)  2018.10  [Refereed]

    DOI

    Scopus

    14
    Citation
    (Scopus)
  • Self-energy renormalization for inhomogeneous nonequilibrium systems and field expansion via complete set of time-dependent wavefunctions

    Y. Kuwahara, Y. Nakamura, Y. Yamanaka

    International Journal of Modern Physics B   32 ( 10 ) 1850111 (22 pages)  2018.04  [Refereed]

     View Summary

    The way to determine the renormalized energy of inhomogeneous systems of a quantum field under an external potential is established for both equilibrium and nonequilibrium scenarios based on thermo field dynamics. The key step is to find an extension of the on-shell concept valid in homogeneous case. In the nonequilibrium case, we expand the field operator by time-dependent wavefunctions that are solutions of the appropriately chosen differential equation, synchronizing with temporal change of thermal situation, and the quantum transport equation is derived from the renormalization procedure. Through numerical calculations of a triple-well model with a reservoir, we show that the number distribution and the time-dependent wavefunctions are relaxed consistently to the correct equilibrium forms at the long-term limit.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Thermal and quantum fluctuations of confined Bose-Einstein condensate beyond the Bogoliubov approximation

    Y. Nakamura, T. Kawaguchi, Y. Torii, Y. Yamanaka

    ANNALS OF PHYSICS   376   484 - 498  2017.01  [Refereed]

     View Summary

    The formulation for zero mode of a Bose-Einstein condensate beyond the Bogoliubov approximation at zero temperature [Y. Nakamura et al., Phys. Rev. A 89 (2014) 013613] is extended to finite temperature. Both thermal and quantum fluctuations are considered in a manner consistent with a concept of spontaneous symmetry breakdown for a finite-size system. Therefore, we need a proper treatment of the zero mode operators, which invoke non-trivial enhancements in depletion condensate and thermodynamical quantities such as the specific heat. The enhancements are visible in the weak interaction case. Our approach reproduces the results of a homogeneous system in the Bogoliubov approximation in a large particle number limit. (C) 2016 Elsevier Inc. All rights reserved.

    DOI

    Scopus

    5
    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

    15
    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

    15
    Citation
    (Scopus)
  • Analytical study of parameter regions of dynamical instability for two-component Bose-Einstein condensates with coaxial quantized vortices

    M. Hoashi, Y. Nakamura, Y. Yamanaka

    PHYSICAL REVIEW A   93 ( 4 )  2016.04  [Refereed]

     View Summary

    The dynamical instability of weakly interacting two-component Bose-Einstein condensates with coaxial quantized vortices is analytically investigated in a two-dimensional isotopic harmonic potential. We examine whether complex eigenvalues appear on the Bogoliubov-de Gennes equation, implying dynamical instability. Rather than solving the Bogoliubov-de Gennes equation numerically, we rely on a perturbative expansion with respect to the coupling constant which enables a simple, analytic approach. For each pair of winding numbers and for each magnetic quantum number, the ranges of intercomponent coupling constant where the system is dynamically unstable are exhaustively obtained. Corotating and counter-rotating systems show distinctive behaviors. The latter is much more complicated than the former with respect to dynamical instability, particularly because radial excitations contribute to complex eigenvalues in counter-rotating systems.

    DOI

    Scopus

    3
    Citation
    (Scopus)
  • Analytical study of parameter regions of dynamical instability for two-component Bose-Einstein condensates with coaxial quantized vortices

    Hoashi, M, Hoashi, M, Nakamura, Y, Yamanaka, Y

    Physical Review A - Atomic, Molecular, and Optical Physics   93 ( 4 ) 043622 (9 pages)  2016.04  [Refereed]

     View Summary

    © 2016 American Physical Society.The dynamical instability of weakly interacting two-component Bose-Einstein condensates with coaxial quantized vortices is analytically investigated in a two-dimensional isotopic harmonic potential. We examine whether complex eigenvalues appear on the Bogoliubov-de Gennes equation, implying dynamical instability. Rather than solving the Bogoliubov-de Gennes equation numerically, we rely on a perturbative expansion with respect to the coupling constant which enables a simple, analytic approach. For each pair of winding numbers and for each magnetic quantum number, the ranges of intercomponent coupling constant where the system is dynamically unstable are exhaustively obtained. Corotating and counter-rotating systems show distinctive behaviors. The latter is much more complicated than the former with respect to dynamical instability, particularly because radial excitations contribute to complex eigenvalues in counter-rotating systems.

    DOI

    Scopus

    3
    Citation
    (Scopus)
  • 19aAC-10 Analysis of Quantum Field Theory on Nα-cluster based on Picture of Bose-Einstein Condensation

    Yamanaka Y., Nakamura Y., Nagai Y., Yosioka R., Ohkubo S.

    Meeting Abstracts of the Physical Society of Japan   71   178 - 178  2016

    DOI CiNii

  • Quantum fluctuations of Bose-Einstein condensates of cold atomic gases in an optical cavity

    Imai Ryosuke, Yamanaka Yoshiya

    Meeting Abstracts of the Physical Society of Japan   71   2905 - 2905  2016

    DOI CiNii

  • 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 ) 023627 (6 pages)  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

    4
    Citation
    (Scopus)
  • 17pPSA-31 Zero mode quantum fluctuation for Bose-Einstein condensate of cold atomic gas with attractive interaction

    Nakamura Y., Kawaguchi T., Yamanaka Y.

    Meeting Abstracts of the Physical Society of Japan   70   2684 - 2684  2015

    DOI CiNii

  • 17pPSA-30 Quantum fluctuation of zero modes for the depletion of the dark soliton

    Kawaguchi T., Nakamura Y., Takahashi J., Yamanaka Y.

    Meeting Abstracts of the Physical Society of Japan   70   2683 - 2683  2015

    DOI CiNii

  • 22pPSB-11 Zero modes and their quantum state for gray soliton in cold atomic gas

    Nakamura Y., Kawaguchi T., Takahashi J., Yamanaka Y.

    Meeting Abstracts of the Physical Society of Japan   70   3047 - 3047  2015

    DOI CiNii

  • 22pPSB-13 Quantum state of soliton and its depletion

    Takahashi J., Nakamura Y., Yamanaka Y.

    Meeting Abstracts of the Physical Society of Japan   70   3049 - 3049  2015

    DOI CiNii

  • 21aAR-2 Linear response of quasiparticle lifetime in Thermo Field Dynamics formalism for cold atomic gas

    Tushima M., Nakamura Y., Kuwahara Y., Imai R., Yamanaka Y.

    Meeting Abstracts of the Physical Society of Japan   70   2835 - 2835  2015

    DOI CiNii

  • 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

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    3
    Citation
    (Scopus)
  • Numerical Analysis of Quantum Transport Equation for Bose Gas in One Dimensional Optical Lattice

    Y. Kuwahara, Y. Nakamura, Y. Yamanaka

    JPS Conf. Proc.   1   012101 (5 pages)  2014.03  [Refereed]

    DOI

  • Relationship between Dynamical Instability and Zero Modes for Dark Soliton in Bose-Einstein Condensate

    J. Takahashi, Y. Nakamura, Y. Yamanaka

    JPS Conf. Proc.   1   012100 (4 pages)  2014.03  [Refereed]

    DOI

  • Analysis of Particle Transfer for Periodic Lattice Modulation in Three Dimensional Optical Lattice

    M. Inoue, Y. Nakamura, Y. Yamanaka

    JPS Conf. Proc.   1   012099 (4 pages)  2014.03  [Refereed]

    DOI

  • Nonequilibrium Thermo Field Dynamics for Thermal Relaxation Process of Confined Cold Atomic Gas

    Y. Nakamura, Y. Kuwahara, Y. Yamanaka

    JPS Conf. Proc.   1   012098 (5 pages)  2014.03  [Refereed]

    DOI

  • Analysis of Particle Transfer by Periodic Lattice Modulation for Ultracold Fermionic Atom Systems in Three-Dimensional Optical Lattice

    Motoyoshi Inoue, Yusuke Nakamura, Yoshiya Yamanaka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 2 ) 024604 (6 pages)  2014.02  [Refereed]

     View Summary

    We analyze an ultracold fermionic atom system in a three-dimensional optical lattice with a confinement harmonic potential, using the Hubbard model and a time-dependent Gutzwiller variational approach to numerical calculation. Our study is focused on the time evolution of particle transfer when the lattice potential is modulated by adding a periodic one. The choice of parameters, such as the modulation frequency, modulation amplitude, and number of particles, affects particle transfer. We calculate the time evolution of the variance in the particle distribution and show its dependences on the parameters. Lattice modulation is found to effectively control particle transfer, and is a useful method in experiments on fermionic atom systems.

    DOI

    Scopus

  • Formulation for the zero mode of a Bose-Einstein condensate beyond the Bogoliubov approximation

    Y. Nakamura, J. Takahashi, Y. Yamanaka

    Physical Review A - Atomic, Molecular, and Optical Physics   89 ( 1 ) 013613 (5 pages)  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. © 2014 American Physical Society.

    DOI

    Scopus

    17
    Citation
    (Scopus)
  • From classical mechanics with doubled degrees of freedom to quantum field theory for nonconservative systems

    Y. Kuwahara, Y. Nakamura, Y. Yamanaka

    PHYSICS LETTERS A   377 ( 43 ) 3102 - 3105  2013.12  [Refereed]

     View Summary

    The 2 x 2-matrix structure of Green's functions is a common feature for the real-time formalisms of quantum field theory under thermal situations, such as the closed time path formalism and Thermo Field Dynamics (TFD). It has been believed to originate from quantum nature. Recently, Galley has proposed the Hamilton's principle with initial data for nonconservative classical systems, doubling each degree of freedom [1]. We show that the Galley's Hamilton formalism can be extended to quantum field and that the resulting theory is naturally identical with nonequilibrium TFD. (C) 2013 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    6
    Citation
    (Scopus)
  • From superoperator formalism to nonequilibrium Thermo Field Dynamics

    Y. Nakamura, Y. Yamanaka

    Annals of Physics   331   51 - 69  2013.04  [Refereed]

     View Summary

    Emphasizing that the specification of the representation space or the quasiparticle picture is essential in nonequilibrium quantum field system, we have constructed the unique unperturbed representation of the interaction picture in the superoperator formalism. To achieve it, we put the three basic requirements (the existence of the quasiparticle picture at each instant of time, the macroscopic causality and the relaxation to equilibrium). From the resultant representation follows the formulation of nonequilibrium Thermo Field Dynamics (TFD). The two parameters, the number distribution and excitation energy, characterizing the representation, are to be determined by the renormalization condition. While we point out that the diagonalization condition by Chu and Umezawa is inconsistent with the equilibrium theory, we propose a new renormalization condition as a generalization of the on-shell renormalization on the self-energy which derives the quantum transport equation and determines the renormalized excitation energy. © 2012 Elsevier Inc.

    DOI

    Scopus

    7
    Citation
    (Scopus)
  • Canonical Quantization for a Relativistic Neutral Scalar Field in Non-Equilibrium Thermo Field Dynamics

    Yuichi Mizutani, Tomohiro Inagaki, Yusuke Nakamura, Yoshiya Yamanaka

    PROGRESS OF THEORETICAL PHYSICS   126 ( 4 ) 681 - 701  2011.10  [Refereed]

     View Summary

    A relativistic neutral scalar held is investigated in non-equilibrium thermo field dynamics. The canonical quantization is applied to the fields out of equilibrium. Because the thermal Bogoliubov transformation becomes time-dependent, the equations of motion for the ordinary unperturbed creation and annihilation operators are modified. This forces us to introduce a thermal counter term in the interaction Hamiltonian which generates additional radiative corrections. Imposing the self-consistency renormalization condition on the total radiative corrections, we obtain the quantum Boltzmann equation for the relativistic scalar field.

    DOI

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    6
    Citation
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  • Effects of finite temperature on the robustness of the Mott insulator phase in pseudo two dimensional Bose-Hubbard model

    M. Inoue, K. Kobayashi, Y. Nakamura, Y. Yamanaka

    J. Phys. B: At. Mol. Opt. Phys.   44 ( 16 ) 165303(9pp)  2011.08  [Refereed]

    DOI

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    1
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  • Effects of finite temperature on the robustness of the Mott insulator phase in a pseudo-two-dimensional Bose-Hubbard model

    Motoyoshi Inoue, Keita Kobayashi, Yusuke Nakamura, Yoshiya Yamanaka

    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS   44 ( 16 ) 165303 (9pp)  2011.08  [Refereed]

     View Summary

    We study the superfluid-Mott insulator (SF-MI) transition in a two-dimensional optical lattice system and employ the Bose-Hubbard model in three dimensions with a combined potential of an optical lattice in two directions and a confining harmonic trap in the other direction, which we refer to as the pseudo-two-dimensional Bose-Hubbard model. Some excited states with respect to the harmonic trap are taken into account in this paper. The Mott lobes shrink in the mu and J directions of the mu-J phase diagram. The shrinkage occurs because the interactions involving the excited states become weaker than that between particles in the ground state. The dispersion of the in-site particle number increases because the energy spacing between the eigenstates of the Hamiltonian decreases at finite temperature. The presence of the excited states significantly affects the robustness of the MI phase at finite temperature.

    DOI

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    1
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  • Extension of Nelson's stochastic quantization to finite temperature using thermo field dynamics

    K. Kobayashi, Y. Yamanaka

    PHYSICS LETTERS A   375 ( 37 ) 3243 - 3249  2011.08  [Refereed]

     View Summary

    We present an extension of Nelson's stochastic quantum mechanics to finite temperature. Utilizing the formulation of Thermo Field Dynamics (TFD), we can show that Ito's stochastic equations for tilde and non-tilde particle positions reproduce the TFD-type Schrodinger equation which is equivalent to the Liouville-von Neumann equation. In our formalism, the drift terms in the Ito's stochastic equation have the temperature dependence and the thermal fluctuation is induced through the correlation of the non-tilde and tilde particles. We show that our formalism satisfies the position-momentum uncertainty relation at finite temperature. (C) 2011 Elsevier B.V. All rights reserved.

    DOI

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    3
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  • Unifying treatment of nonequilibrium and unstable dynamics of cold bosonic atom system with time-dependent order parameter in Thermo Field Dynamics

    Y. Nakamura, Y. Yamanaka

    ANNALS OF PHYSICS   326 ( 4 ) 1070 - 1083  2011.04  [Refereed]

     View Summary

    The coupled equations which describe the temporal evolution of the Bose-Einstein condensed system are derived in the framework of nonequilibrium Thermo Field Dynamics. The key element is that they are not the naive assemblages of assumed equations, but are the self-consistent ones derived by appropriate renormalization conditions. While the order parameter is time-dependent, an explicit quasiparticle picture is constructed by a time-dependent expansion. Our formulation is valid even for the system with a unstable condensate, and describes the condensate decay caused by the Landau instability as well as by the dynamical one. (C) 2010 Elsevier Inc. All rights reserved.

    DOI

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    6
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  • Nelson's Stochastic Quantization in Thermo Field Dynamics

    Soryushiron Kenkyu Electronics   118 ( 4 ) D153 - D155  2011

    DOI CiNii

  • Derivation of non-Markovian transport equations for trapped cold atoms in nonequilibrium thermal field theory

    Y. Nakamura, T. Sunaga, M. Mine, M. Okumura, Y. Yamanaka

    ANNALS OF PHYSICS   325 ( 2 ) 426 - 441  2010.02  [Refereed]

     View Summary

    The non-Markovian transport equations for the systems of cold Bose atoms confined by a external potential both without and with a Bose-Einstein condensate are derived in the framework of non-equilibrium thermal field theory (Thermo Field Dynamics). Our key elements are an explicit particle representation and a self-consistent renormalization condition which are essential in thermal field theory. The non-Markovian transport equation for the non-condensed system, derived at the two-loop level, is reduced in the Markovian limit to the ordinary quantum Boltzmann equation derived in the other methods. For the condensed system, we derive a new transport equation with an additional collision term which becomes important in the Landau instability. (C) 2009 Elsevier Inc. All rights reserved.

    DOI

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    6
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  • 凝縮体がある冷却原子系の非平衡Thermo Field Dynamics(非平衡系,熱場の量子論とその応用,研究会報告)

    中村 祐介, 須永 知夏, 峰 真如, 奥村 雅彦, 山中 由也

    素粒子論研究   118 ( 1 ) A8 - A10  2010

    DOI CiNii

  • Analytical study of the splitting process of a multiply-quantized vortex in a Bose-Einstein condensate and collaboration of the zero and complex modes

    K. Kobayashi, Y. Nakamura, M. Mine, Y. Yamanaka

    ANNALS OF PHYSICS   324 ( 11 ) 2359 - 2371  2009.11  [Refereed]

     View Summary

    We study the dynamics of a trapped Bose-Einstein condensate with a multiply-quantized vortex, and investigate the roles of the fluctuations in the dynamical evolution of the system. Using the perturbation theory of the external potential, and assuming the situation of the small coupling constant of self-interaction, we analytically solve the time-dependent Gross-Pitaevskii equation. We introduce the zero mode and its adjoint mode of the Bogoliubov-de Gennes equations. Those modes are known to be essential for the completeness condition. We confirm how the complex eigenvalues induce the vortex splitting. It is shown that the physical role of the adjoint zero mode is to ensure the conservation of the total condensate number. The contribution of the adjoint mode is exponentially enhanced in synchronism with the exponential growth of the complex mode, and is essential in the vortex splitting. (C) 2009 Elsevier Inc. All rights reserved.

    DOI

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    6
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    (Scopus)
  • Nonequilibrium TFD for systems of trapped cold atoms

    Y. Yamanaka, M. Okumura, M. Mine, Y. Nakamura

    素粒子論研究   116 ( 6 ) F75 - F77  2009.02

    DOI CiNii

  • Quantum field theoretical analysis on unstable behavior of Bose-Einstein condensates in optical lattices

    K. Kobayashi, M. Mine, M. Okumura, Y. Yamanaka

    ANNALS OF PHYSICS   323 ( 5 ) 1247 - 1270  2008.05  [Refereed]

     View Summary

    We study the dynamics of Bose-Einstein condensates flowing in optical lattices on the basis of quantum field theory. For such a system, a Bose-Einstein condensate shows an unstable behavior which is called the dynamical instability. The unstable system is characterized by the appearance of modes with complex eigenvalues. Expanding the field operator in terms of excitation modes including complex ones, we attempt to diagonalize the unperturbative Hamiltonian and to find its eigenstates. It turns out that although the unperturbed Hamiltonian is not diagonalizable in the conventional bosonic representation the appropriate choice of physical states leads to a consistent formulation. Then we analyze the dynamics of the system in the regime of the linear response theory. Its numerical results are consistent with those given by the discrete nonlinear Schrodinger equation. (c) 2007 Elsevier Inc. All rights reserved.

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  • Condition for emergence of complex eigenvalues in the Bogoliubov-de Gennes equations

    Y. Nakamura, M. Mine, M. Okumura, Y. Yamanaka

    PHYSICAL REVIEW A   77 ( 4 ) 043601  2008.04  [Refereed]

     View Summary

    The condition for the appearance of dynamical instability of the Bose-condensed system, characterized by the emergence of complex eigenvalues in the Bogoliubov-de Gennes equations, is studied analytically. It is concluded that the degeneracy between a positive-norm eigenmode and a negative-norm one is essential for the emergence of complex modes. Based on the conclusion, we justify the two-mode approximation applied in our previous work [E. Fukuyama , Phys. Rev. A 76, 043608 (2007)], in which we analytically studied the condition for the existence of complex modes when the condensate has a highly quantized vortex.

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    20
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  • 解析的手法によるBose-Einstein Condensateにおける複素モード出現条件(熱場の量子論とその応用,研究会報告)

    中村 祐介, 峰 真如, 奥村 雅彦, 山中 由也

    素粒子論研究   116 ( 2 ) B67 - B69  2008

    DOI CiNii

  • Condition for the existence of complex modes in a trapped Bose-Einstein condensate with a highly quantized vortex

    E. Fukuyama, M. Mine, M. Okumura, T. Sunaga, Y. Yamanaka

    PHYSICAL REVIEW A   76 ( 4 )  2007.10  [Refereed]

     View Summary

    We consider a trapped Bose-Einstein condensate (BEC) with a highly quantized vortex. For the BEC with a doubly, triply, or quadruply quantized vortex, the numerical calculations have shown that the Bogoliubov-de Gennes equations, which describe the fluctuation of the condensate, have complex eigenvalues. In this paper, we obtain the analytic expression of the condition for the existence of complex modes, using the method developed by Rossignoli and Kowalski [R. Rossignoli and A. M. Kowalski, Phys. Rev. A 72, 032101 (2005)] for the small coupling constant. To derive it, we make the two-mode approximation. With the derived analytic formula, we can identify the quantum numbers of the complex modes for each winding number of the vortex. Our result is consistent with those obtained by the numerical calculation in the case that the winding number is two, three, or four. We prove that the complex modes always exist when the condensate has a highly quantized vortex.

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    6
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  • Quantum field theoretical description of unstable behavior of trapped Bose-Einstein condensates with complex eigenvalues of Bogoliubov-de Gennes equations

    Makoto Mine, Masahiko Okumura, Tomoka Sunaga, Yoshiya Yamanaka

    ANNALS OF PHYSICS   322 ( 10 ) 2327 - 2349  2007.10  [Refereed]

     View Summary

    7 The Bogoliubov-de Gennes equations are used for a number of theoretical works on the trapped Bose-Einstein condensates. These equations are known to give the energies of the quasi-particles when all the eigenvalues are real. We consider the case in which these equations have complex eigenvalues. We give the complete set including those modes whose eigenvalues are complex. The quantum fields which represent neutral atoms are expanded in terms of the complete set. It is shown that the state space is an indefinite metric one and that the free Hamiltonian is not diagonalizable in the conventional bosonic representation. We introduce a criterion to select quantum states describing the metastablity of the condensate, called the physical state conditions. In order to study the instability, we formulate the linear response of the density against the time-dependent external perturbation within the regime of Kubo's linear. response theory. Some states, satisfying all the physical state conditions, give the blow-up and damping behavior of the density distributions corresponding to the complex eigenmodes. It is qualitatively consistent with the result of the recent analyses using the time-dependent Gross-Pitaevskii equation. (c) 2007 Elsevier Inc. All rights reserved.

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    15
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  • Condition for the existence of complex modes in a trapped Bose-Einstein condensate with a highly quantized vortex (vol 76, art no 043608, 2007)

    E. Fukuyama, M. Mine, M. Okumura, T. Sunaga, Y. Yamanaka

    PHYSICAL REVIEW A   76 ( 4 ) 43608  2007.10  [Refereed]

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  • The condition for existence of complex modes in trapped Bose-Einstein condensate with a highly quantized vortex

    Tomoka Sunaga, Eriko Fukuyama, Makoto Mine, Masahiko Okumura, Yoshiya Yamanaka

    JOURNAL OF LOW TEMPERATURE PHYSICS   148 ( 3-4 ) 381 - 386  2007.08  [Refereed]

     View Summary

    We consider a trapped Bose-Einstein condensate with a highly quantized vortex. Pu et al. found numerically the parameter region in which complex eigenvalues arise. Recently, the splitting of a highly quantized vortex into two singly quantized vortices is observed in the experiment. We derive analytically the condition for the existence of complex eigenvalues by using the small coupling constant expansion and the two-mode approximation. We check that our results agree with those by Pu et al.

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    2
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  • Quantum field theoretical description of dynamical instability of trapped Bose-Einstein condensates

    Makoto Mine, Masahiko Okumura, Tomoka Sunaga, Yoshiya Yamanaka

    JOURNAL OF LOW TEMPERATURE PHYSICS   148 ( 3-4 ) 331 - 336  2007.08  [Refereed]

     View Summary

    The Bogoliubov-de Gennes equations are used for a number of theoretical works on the trapped Bose-Einstein condensates. We consider the case in which these equations have complex eigenvalues. We give the complete set including a pair of complex modes whose eigenvalues are complex conjugate to each other. The expansion of the quantum fields which represent neutral atoms in terms of the complete set brings about the operators associated with the complex modes, which are simply neither bosonic nor fermionic ones. The eigenstate of the Hamiltonian is given. Introducing the notion of the physical states, we discuss the instability of the condensates in the context of Kubo's linear response theory.

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    Scopus

    3
    Citation
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  • Quantum field theoretical description of unstable behavior of a Bose-Einstein condensate with a highly quantized vortex in a harmonic potential

    M. Okumura, M. Mine, T. Sunaga, Y. Yamanaka

    LASER PHYSICS   17 ( 2 ) 211 - 214  2007.02  [Refereed]

     View Summary

    The Bogoliubov-de Gennes equations are used for a number of theoretical works to describe quantum and thermal fluctuations of trapped Bose-Einstein condensates. We consider the case in which the condensate has a highly quantized vortex. It is known that these equations have complex eigenvalues in this case. We give the complete set including a pair of complex modes whose eigenvalues are complex conjugates to each other. The expansion of the quantum fields which represent neutral atoms in terms of the complete set brings the operators associated with the complex modes, which are simply neither bosonic nor fermionic ones. The eigenstate of the Hamiltonian is given. Introducing the notion of the physical states, we discuss the instability of the condensates in the context of Kubo's linear response theory.

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    Scopus

  • Complex Eigenvalues Associated with Trapped BEC and Field Theoretical Description of Unstable Behavior

    M. Mine, M. Okumura, Y. Yamanaka

    素粒子論研究   114 ( 3 ) C24 - C26  2006.12

    DOI CiNii

  • Goldstone theorem, Hugenholtz-Pines theorem, and Ward-Takahashi relation in finite volume Bose-Einstein condensed gases

    Hiroaki Enomoto, Masahiko Okumura, Yoshiya Yamanaka

    ANNALS OF PHYSICS   321 ( 8 ) 1892 - 1917  2006.08  [Refereed]

     View Summary

    We construct an approximate scheme based on the concept of the spontaneous symmetry breakdown, satisfying the Goldstone theorem, for finite volume Bose-Einstein condensed gases in both zero and finite temperature cases. In this paper, we discuss the Bose-Einstein condensation in a box with periodic boundary condition and do not assume the thermodynamic limit. When energy spectrum is discrete, we found that it is necessary to deal with the Nambu-Goldstone mode explicitly without the Bogoliubov's prescription, in which zero-mode creation- and annihilation-operators are replaced with a c-number by hand, for satisfying the Goldstone theorem. Furthermore, we confirm that the unitarily inequivalence of vacua in the spontaneous symmetry breakdown is true for the finite volume system. (c) 2006 Elsevier Inc. All rights reserved.

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    8
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  • Unitarily inequivalent vacua in Bose-Einstein condensation of trapped gases

    Masahiko Okumura, Yoshiya Yamanaka

    PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS   365 ( 2 ) 429 - 445  2006.06  [Refereed]

     View Summary

    We approach the problem of the Bose-Einstein condensation of neutral atoms in an external trap, which is a finite system in size, from the viewpoint of quantum field theory. The phenomenon is considered as a spontaneous symmetry breakdown. The main result of this paper is that the vacua for this system with finite size and finite number of trapped neutral atoms, parametrized by different phases of the order parameter, are orthogonal to each other, namely the Fock spaces associated with each vacuum are unitarily inequivalent to each other. In the proof, the zero-energy mode which is the Nambu-Goldstone mode, and is discrete due to the presence of the trap, plays a crucial role. We introduce the discrete zero-energy mode in the formulation of the generalized Bogoliubov transformation and introduce an additional infinitesimal symmetry-breaking term in the Hamiltonian to control the zero-energy mode properly. (c) 2005 Elsevier B.V. All rights reserved.

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    2
    Citation
    (Scopus)
  • Effect of the zero-mode on the response of a trapped bose-condensed gas

    M Mine, T Koide, M Okumura, Y Yamanaka

    PROGRESS OF THEORETICAL PHYSICS   115 ( 4 ) 683 - 700  2006.04  [Refereed]

     View Summary

    The dynamical response of a trapped Bose-Einstein condensate (BEC) is formulated consistently with quantum field theory and is numerically evaluated. We regard the BEC as a manifestation of the breaking of the global phase symmetry. Then, the Goldstone theorem implies the existence of a zero energy excitation mode (the zero-mode). We calculate the effect of the zero-mode on the response frequency and show that the contribution of the zero-mode to the first excitation mode is not so important in the parameter set realized in the existing experiment. This is the reason that experimental results can be described using the Bogoliubov prescription, although it breaks the consistency of the description in quantum field theory.

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    2
    Citation
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  • Effect of zero mode on the response of napped bose-condensed atoms

    M. Mine, T. Koide, M. Okumura, Y. Yamanaka

    THIRD 21COE SYMPOSIUM: ASTROPHYSICS AS INTERDISCIPLINARY SCIENCE   31   211 - +  2006  [Refereed]

     View Summary

    The response of the trapped Bose-Einstein condensate (BEC) is investigated. We regard the BEC as a manifestation of the spontaneous breakdown of the global phase symmetry. Then, the Goldstone theorem leads to the existence of the zero energy excitation mode (zero-mode). We calculate the effect of the zero-mode to the response frequency and show that the contribution of the zero-mode to the first excitation mode becomes dominant as the temperature and/or the coupling constant are increased.

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  • Approximate scheme satisfying the Goldstone theorem in finite volume Bose-Einstein condensed gas

    H. Enomoto, M. Okumura, Y. Yamanaka

    素粒子論研究   112 ( 3 ) C55 - C57  2005.12

    DOI CiNii

  • Bose-Einstein condensation and macroscopic wave function in quantum field theory

    M. Okumura, M. Mine, Y. Yamanaka

    素粒子論研究   112 ( 3 ) C45 - C54  2005.12

    DOI CiNii

  • Relation between generalized Bogoliubov and Bogoliubov-de Gennes approaches including Nambu-Goldstone mode

    M Mine, M Okumura, Y Yamanaka

    JOURNAL OF MATHEMATICAL PHYSICS   46 ( 4 ) 42307  2005.04  [Refereed]

     View Summary

    The two approaches of consistent quantum field theory for systems of the trapped Bose-Einstein condensates are known, one is the Bogoliubov-de Gennes approach and the other is the generalized Bogoliubov approach. In this paper, we investigate the relation between the two approaches and show that they are formally equivalent to each other. To do this one must carefully treat the Nambu-Goldstone mode which plays a crucial role in the condensation. It is emphasized that the choice of vacuum is physically relevant. (C) 2005 American Institute of Physics.

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    9
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  • Ward-Takahashi relation at finite temperature in Bose-Einstein condensation of trapped neutral atoms

    M Okumura, Y Yamanaka

    PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS   348   157 - 172  2005.03  [Refereed]

     View Summary

    We prove that the Ward-Takahashi relations at finite temperature are satisfied at the tree level for a system of a trapped Bose-Einstein condensate when the zero mode is included in the quasi-particle picture property. This implies that the zero mode represents the Nambu-Goldstone mode and that it is introduced in a way consistent with the Goldstone theorem. In the proof, we employ thermo field dynamics which is a real-time operator formalism of quantum field theory at finite temperature. (C) 2004 Published by Elsevier B.V.

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    5
    Citation
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  • Renormalization condition on self-energy at two-loop level for trapped atomic gas

    M. Okumura, Y. Yamanaka

    素粒子論研究   110 ( 5 ) E16 - E18  2005.02

    DOI CiNii

  • Renormalization condition in trapped Bose-Einstein condensation

    M. Okumura, Y. Yamanaka

    素粒子論研究   108 ( 5 ) E43 - E45  2004.02

    DOI CiNii

  • Effects of quantum coordinates on condensate density in a trapped Bose-Einstein condensate

    M Okumura, Y Yamanaka

    PROGRESS OF THEORETICAL PHYSICS   111 ( 2 ) 199 - 211  2004.02  [Refereed]

     View Summary

    The effects of quantum coordinates associated with the Nambu-Goldstone mode in a trapped Bose-Einstein condensate are investigated at zero and finite temperatures. We develop a loop expansion and perform numerical calculations over a wide range of temperature, i.e., between zero and the critical temperatures. Our results are compared with those obtained in cases without the Nambu-Goldstone mode (the Bogoliubov approximation) and with the Nambu-Goldstone mode as a zero-energy particle mode.

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    6
    Citation
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  • Analysis of response of trapped Bose-Einstein condensates with Nambu-Goldstone mode

    Soryushiron Kenkyu Electronics   108 ( 5 ) E40 - E42  2004

    DOI CiNii

  • Response of trapped Bose-Einstein condensates under time-dependent perturbation

    T. Koide, M. Mine, M. Okumura, Y. Yamanaka

    Journal of Modern Optics   51-6 ( 7 ) 1103 - 1104  2004  [Refereed]

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    1
    Citation
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  • Nambu-Goldstone mode in trapped bose-einstein condensation

    M. Okumura, Y. Yamanaka

    Journal of Modern Optics   51-6 ( 7 ) 1101 - 1102  2004  [Refereed]

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  • Role of Nambu-Goldstone Mode in Trapped Bose-Einstein Condensation

    Y. Yamanaka, M. Okumura, M. Mine

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72   152 - 155  2003.11  [Refereed]

     View Summary

    The system of the trapped Bose-Einstein condensation is investigated from the viewpoint of Quantum Field Theory. It is pointed out that the Nambu-Goldstone mode, which is a discrete mode due to the trapping potential, creates observable effects through fluctuations. The way how the Nambu-Goldstone mode is treated is not unique. The introduction of quantum coordinates is a possible candidate.

  • Proper treatment of the zero mode in quantum field theory for trapped Bose-Einstein condensation

    M Okumura, Y Yamanaka

    PHYSICAL REVIEW A   68 ( 1 ) 13609 - 13620  2003.07  [Refereed]

     View Summary

    So far much theoretical consideration of experiments on the Bose-Einstein condensation (BEC) of alkali-metal atoms in harmonic traps is based on the Gross-Pitaevskii (GP) equation. In this paper, we attempt to formulate the BEC in the language of quantum field theory and to estimate the quantum and thermal fluctuation effects, which are neglected in the approximation using the GP equation. First, the formulation at zero temperature is developed, and then it is extended to the finite-temperature case by means of thermofield dynamics. We treat the zero-energy mode with care, so that the canonical commutation relations hold. As a result, an infrared divergence appears, but it can be renormalized into the observed condensate number. Numerical calculations are performed. For illustration, the corrections at one-loop level to the original GP equation are given. We also calculate numerically the effects of quantum and thermal fluctuations on the distribution of condensed atoms.

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  • The Role of Nambu-Goldstone Mode in Trapped Bose-Einstein Condensates

    M. Okumura, Y. Yamanaka

    素粒子論研究/京都大学   106 ( 5 ) E12 - E12  2003.02

    DOI CiNii

  • Proper treatment of the zero mode in quantum field theory for trapped Bose-Einstein condensation

    M. Okumura, Y. Yamanaka

    Physical Review A - Atomic, Molecular, and Optical Physics   68 ( 1 ) 12  2003  [Refereed]

     View Summary

    So far much theoretical consideration of experiments on the Bose-Einstein condensation (BEC) of alkali-metal atoms in harmonic traps is based on the Gross-Pitaevskii (GP) equation. In this paper, we attempt to formulate the BEC in the language of quantum field theory and to estimate the quantum and thermal fluctuation effects, which are neglected in the approximation using the GP equation. First, the formulation at zero temperature is developed, and then it is extended to the finite-temperature case by means of thermofield dynamics. We treat the zero-energy mode with care, so that the canonical commutation relations hold. As a result, an infrared divergence appears, but it can be renormalized into the observed condensate number. Numerical calculations are performed. For illustration, the corrections at one-loop level to the original GP equation are given. We also calculate numerically the effects of quantum and thermal fluctuations on the distribution of condensed atoms. © 2003 The American Physical Society.

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  • The Analysis of Nambu-Goldstone mode in trapped Bose--Einstein condensates

    M. Okumura, Y. Yamanaka

    素粒子論研究   105 ( 1 ) A89 - A91  2002.04

     View Summary

    We analyze the Nambu-Goldstone (NG) mode for a system of trapped Bose-Einstein condensation (BEC). The NG mode is a discrete mode in our case, contrary to the homogeneous case in which the NG mode is in a continuum labeled by a momentum index. In order to control the NG mode, an infinitesimal symmetry-breaking term is introduced. This breaking term plays the role of infinitesimal magnetic field in spin system which fixes the macroscopic "direction" of spin. We calculate a tadpole diagram to evaluate fluctuation effects, taking account of the NG mode, then find that the coefficient of the wave function of condensation is infrared divergent while the remaining terms are finite.

    DOI CiNii

  • Nonequilibrium TFD (Thrmo Field Dynamics)-Review

    Y. Yamanaka

    素粒子論研究   105 ( 1 ) A73 - A82  2002.04

     View Summary

    Nonequilibrium Thermo Field Dynamics (TFD) is reviewed. The aspect that nonequilibrium TFD respects Quantum Field Theory is emphasized. A new type of renormalization condition, implying a self-consistent treatment, plays an important role. We also comment on the correspondence between TFD and the conventional density matrix formalism. The recent experiments of the Bose-Einstein condensation of neutral atoms are expected to offer a test field for thermal field theories.

    DOI CiNii

  • Numerical Analysis of Bose-Einstein condensation in a harmonic potential formulated by thermal field theory

    M. Okumura, Y. Yamanaka

    素粒子論研究   103 ( 1 ) A35 - A38  2001.04

     View Summary

    The Bose-Einstein condensation in recent experiments is formulated as a problem in thermal quantum field theory. From this formulation, we carry out numerical analysis so as to investigate effects of quantum and thermal fluctuation to the condensate phase and properties of quasi-particles in this situation.

    DOI CiNii

  • Quantum Correction to the Gross-Pitaevskii Equation in a Bose--Einstein Condensate

    M. Okumura, Y. Yamanaka

    物性研究   75 ( 5 ) 1039 - 1049  2001.02

     View Summary

    So far many theoretical considerations for experiments of Bose-Einstein condensation (BEC) of alkali atoms in harmonic traps are based on the Gross-Pitaevskii (GP) equation. In this report, we attempt to formulate the BEC in the language of quantum field theory in order to go beyond the approximation of GP equation. First the formulation at zero-temperature is presented, and then it is extended to finite-temperature case by means of Thermo Field Dynamics. Numerical calculations, which are inevitable even in the unperturbative formulation of our approach, are performed. For illustration, the corrections at one-loop level to the original GP equation are given. We also calculate the effects of quantum and thermal fluctuations to the distribution of condensed atoms numerically.

    CiNii

  • Description of Bose-Einstein condensation in a harmonic potential by quantum field theory

    M. Okumura, Y. Yamanaka

    素粒子論研究   100 ( 5 ) E110 - E113  2000.02

     View Summary

    Experiments of Bose-Einstein condensation (BEC) of alkali atoms in harmonic traps which were achieved successfully have inspired various theoretical studies. So far many theoretical considerations are based on the Gross-Pitaevskii equation. In this report, we attempt to formulate the BEC in the language of quantum field theory, so that effects of quantum fluctuation can be estimated properly.

    DOI CiNii

  • Fluctuation of the Bose-Einstein condensate in a trap

    H. Ezawa, K. Nakamura, K. Watanabe, Y. Yamanaka

    Mathematical Physics and Stochastic Analysis-Essays in Honour of Ludwig Streit/ World Scientific     169 - 183  2000.01  [Refereed]

  • Tunneling time based on the quantum diffusion process approach in multi-channel and optical potential cases

    Ohba, I, K Imafuku, Y Yamanaka

    PRAMANA-JOURNAL OF PHYSICS   51 ( 5 ) 603 - 614  1998.11  [Refereed]

     View Summary

    We analyze the effects of inelastic scattering on the tunneling time theoretically, using generalized Nelson's quantum mechanics. This generalization enables us to describe quantum system with channel couplings and optical potential in a real time stochastic approach, which seems to give us a new insight into quantum mechanics beyond Copenhagen interpretation.

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  • Tunneling time and Nelson's Quantum Mechanics

    Imafuku Kentaro, Ohba Ichiro, Yamanaka Yoshiya

    京都大学数理解析研究所講究録   982   30 - 40  1997.03

    CiNii

  • Effects of inelastic scattering on tunneling time based on the generalized diffusion process approach

    Kentaro Imafuku, Ichiro Ohba, Yoshiya Yamanaka

    Physical Review A - Atomic, Molecular, and Optical Physics   56 ( 2 ) 1142 - 1153  1997  [Refereed]

     View Summary

    We analyze the effects of inelastic scattering on the tunneling time theoretically, using generalized Nelson’s quantum mechanics. This generalization enables us to describe a quantum system with optical potential and channel couplings in a real-time stochastic approach, which seems to give us a new insight into quantum mechanics beyond Copenhagen interpretation. © 1997 The American Physical Society.

    DOI

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    26
    Citation
    (Scopus)
  • Concept of quasiparticle in thermofield dynamics for nonequilibrium systems

    Y Yamanaka, K Nakamura

    PHYSICS ESSAYS   9 ( 4 ) 617 - 623  1996.12  [Refereed]

     View Summary

    The concept of quasiparticle (representation particle) is a central issue when thermofield dynamics (TFD) for nonequilibrium systems of quantum fields is constructed. The development of nonequilibrium TFD, mainly clone by the Alberta group, is reviewed from the viewpoint of the quasiparticle.

  • Quantum dephasing by chaos

    H Nakazato, M Namiki, S Pascazio, Y Yamanaka

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

     View Summary

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

  • Diffusion in inhomogeneous TFD

    Y. Yamanaka, K. Nakamura

    Thermal Field Theories and Their Applications/World Scientific     71 - 83  1996.06  [Refereed]

  • Quasi particle modes in spatially inhomogeneous thermo field dynamics

    K.Nakamura, Y. Yamanaka

    Thermal Field Theories and Their Applications/World Scientific     23 - 31  1996.06  [Refereed]

  • Thermal field theory in non-equilibrium states

    PA Henning, K Nakamura, Y Yamanaka

    INTERNATIONAL JOURNAL OF MODERN PHYSICS B   10 ( 13-14 ) 1599 - 1614  1996.06  [Refereed]

     View Summary

    Conventional transport theory is not really applicable to nonequilibrium systems which exhibit strong quantum effects. We present two different approaches to overcome this problem. Firstly we point out how transport equations may be derived that incorporate a nontrivial spectral function as a typical quantum effect, and test this approach in a toy model of a strongly interacting degenerate plasma. Secondly we explore a path to include nonequilibrium effects into quantum field theory through momentum mixing transformations in Fock space. Although the two approaches are completely orthogonal, they lead to the same coherent conclusion.

    DOI

  • Estimation of tunneling time based on the quantum diffusion process approach and netron scattering

    I. Ohba, K. Imafuku, Y. Yamanaka

    J. Phys. Soc. Jpn. Suppl. A   65   41 - 44  1996  [Refereed]

  • Development of nonequilibrium TFD

    Y. Yamanaka

    Field Theory and Collective Phenomena/World Scientific     237 - 249  1995.12  [Refereed]

  • TUNNELING TIME-BASED ON THE QUANTUM DIFFUSION PROCESS APPROACH

    K IMAFUKU, OHBA, I, Y YAMANAKA

    PHYSICS LETTERS A   204 ( 5-6 ) 329 - 335  1995.08  [Refereed]

     View Summary

    We present a time-dependent description of tunneling phenomena, using Nelson's stochastic approach. It appears to be capable to describe individual experimental runs, and provides a new insight into quantum measurement processes. We propose a new way to evaluate the tunneling time in this approach and give the results of numerical simulations.

  • ENTROPY LAW FROM INHOMOGENEOUS THERMOFIELD DYNAMICS

    Y YAMANAKA, K NAKAMURA

    MODERN PHYSICS LETTERS A   9 ( 31 ) 2879 - 2891  1994.10  [Refereed]

     View Summary

    In the framework of thermofield dynamics for spatially inhomogeneous time-dependent nonequilibrium situations, we derive the kinetic equation, which is different from the Boltzmann equation due to quantum effects. It is shown that this kinetic equation leads to the entropy law. An expression for the entropy how is found.

    DOI

  • Transport theory for quark-gluon plasma based on an operator field Langevin equation

    M. Namiki, Y. Yamanaka, S. Muroya

    物性研究   62 ( 1 ) 171 - 181  1994.04

    CiNii

  • THERMO-FIELD DYNAMICS IN TIME REPRESENTATION

    Y YAMANAKA, H UMEZAWA, K NAKAMURA, T ARIMITSU

    INTERNATIONAL JOURNAL OF MODERN PHYSICS A   9 ( 7 ) 1153 - 1180  1994.03  [Refereed]

     View Summary

    Making use of the thermo field dynamics (TFD) we formulate a calculable method for time-dependent nonequilibrium systems in a time representation (t-representation) rather than in the k0-Fourier representation. The corrected one-body propagator in the t-representation has the form of B-1 (diagonal matrix) B (B being a thermal Bogoliubov matrix). The number parameter in B here is the observed number (the Heisenberg number) with a fluctuation. With the usual definition of the on-shell self-energy a self-consistent renormalization condition leads to a kinetic equation for the number parameter. This equation turns out to be the Boltzmann equation, from which the entropy law follows.

    DOI

  • A TIME-DEPENDENT NONEQUILIBRIUM CALCULATIONAL SCHEME TOWARDS THE STUDY OF TEMPERATURE-FLUCTUATIONS

    TS EVANS, HARDMAN, I, H UMEZAWA, Y YAMANAKA

    FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS   41 ( 2 ) 151 - 175  1993  [Refereed]

     View Summary

    A new perturbative scheme for interacting nonequilibrium thermal quantum fields using thermo field dynamics is outlined by explicitly considering the temporal change of the thermal vacuum as it moves through many inequivalent state vector spaces. One is then naturally led to two sources of time dependence, one from the dynamics and the other from the change of thermal vacuum, which are taken care of by the Hamiltonian and the thermal generator, respectively. To obtain a practical scheme we restrict ourselves by the demand that a spectral representation for the full propagator exists. This leads to a time dependent temperature. The addition of a diagonalization condition for the quasi-particle Hamiltonian provides the master equation for the number density. We show that our formalism is equivalent to an extended form of the path-ordering method. This formalism is a first step towards the study of the origin of heat and temperature in high-energy heavy ion collisions.

    DOI

  • NONEQUILIBRIUM THERMOFIELD DYNAMICS - IN TIME REPRESENTATION

    Y YAMANAKA

    VISTAS IN ASTRONOMY, VOL 37, PTS 1-4   37   93 - 97  1993  [Refereed]

  • QUANTUM-FIELD THEORY WITH FICTITIOUS TIME IN STOCHASTIC QUANTIZATION

    Y YAMANAKA

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   111 ( 111 ) 417 - 431  1993  [Refereed]

     View Summary

    A model with spontaneous breakdown of symmetry in quantum field theory is studied in the framework of the Parisi-Wu stochastic quantization (SQ). Looking at the conventional treatment of the model in the canonical and the path-integral quantizations including the problems of many inequivalent Hilbert spaces and measures, we explicitly construct the SQ formulation for the model in the conventional treatment of quantum field theory. The real power of SQ is found in extending quantum field theory beyond the existing frameworks; SQ easily avoids the problems imposed by choices of Hilbert space or measure. We demonstrate it by introducing c-numbers depending on the fictitious time into the starting formal Langevin equations for the model. This new formulation in SQ thus obtained is mathematically well-defined, leading to a definite calculational scheme. The result from this shows that the masses and number of excitation modes change from those in the conventional treatment.

    DOI

  • TEMPORAL DESCRIPTION OF THERMAL QUANTUM-FIELDS

    H UMEZAWA, Y YAMANAKA

    MODERN PHYSICS LETTERS A   7 ( 37 ) 3509 - 3520  1992.12  [Refereed]

     View Summary

    By making use of time-dependent Bogoliubov transformations, we develop a calculation technique for time-dependent non-equilibrium systems of quantum fields in a time-representation (t-representation). The corrected one-body propagator in the t-representation turns out to have the form B-1 (diagonal matrix) B (B being a thermal Bogoliubov matrix). Applying the usual on-shell concept to the diagonal matrix part of the self-energy, we formulate a self-consistent renormalization scheme. This renormalization determines the vacuum and leads to a kinetic equation for the number density parameter, which reduces to the Boltzmann equation in the lowest approximation. This gives us the increasing entropy in time (the second law of thermodynamics).

    DOI

  • TIME-SPACE DEPENDENT FORMULATION IN THERMOFIELD DYNAMICS

    K NAKAMURA, H UMEZAWA, Y YAMANAKA

    MODERN PHYSICS LETTERS A   7 ( 38 ) 3583 - 3592  1992.12  [Refereed]

     View Summary

    The recently developed formulation of time-dependent non-equilibrium thermofield dynamics (TFD) is extended to spatially inhomogeneous field systems in this paper. This inhomogeneous formalism is constructed from introducing momentum mixing thermal Bogoliubov transformation. The momentum mixing number density in the Bogoliubov matrix is related to the number density distribution defined at each space-time point which is to be observed.

    DOI

  • Time-dependent TFD

    Y. Yamanaka

    物性研究   59   197 - 202  1992.11

  • HEISENBERG AND INTERACTION REPRESENTATIONS IN THERMO FIELD-DYNAMICS

    TS EVANS, HARDMAN, I, H UMEZAWA, Y YAMANAKA

    JOURNAL OF MATHEMATICAL PHYSICS   33 ( 1 ) 370 - 378  1992.01  [Refereed]

     View Summary

    In this paper the so-called a degree of freedom appearing in thermal quantum field theory is discussed, using thermo field dynamics (TFD). This paper is confined to stationary thermal situations, both nonequilibrium and equilibrium. The main result is that when the stationary number distribution differs from the equilibrium one the use of time ordered and antitime ordered formalisms picks up alpha = 1 and alpha = 0, in contrast to the general belief that the Feynman diagram method is usable for any other alpha as well. This situation in TFD will be compared with the other approaches. The reason why the Feynman diagram method becomes available for any alpha in the case of the equilibrium distributions is also studied.

    DOI

    Scopus

    27
    Citation
    (Scopus)
  • ON CLASSICAL PROPERTIES OF THERMAL SQUEEZED STATES

    A MANN, M REVZEN, H UMEZAWA, Y YAMANAKA

    JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL   24 ( 19 ) 4527 - 4533  1991.10  [Refereed]

     View Summary

    We use the formalism of thermo field dynamics and the classical Cramer's theorem to show that if two quantum systems are prepared independently and their centre of mass is found to be a thermal squeezed state, then both systems were prepared in thermal squeezed states. This constitutes an alternative derivation of the quantum version of Cramer's theorem. Further, we consider the case of two systems that are prepared independently and their centre of mass is in a pure state in the expanded space of thermo field dynamics. In this case we show that the system is also separable in the centre of mass and relative coordinates, and again all the states involved are thermal squeezed states.

  • THERMAL DEGREE OF FREEDOM IN THERMO FIELD-DYNAMICS

    H UMEZAWA, Y YAMANAKA

    PHYSICS LETTERS A   155 ( 2-3 ) 75 - 82  1991.05  [Refereed]

     View Summary

    The view of the thermal degree of freedom for the quantum field system, using the language of thermo field dynamics, is elaborated in this paper: the thermal degree of freedom is the degree of freedom to move through degenerate thermal vacua associated with spontaneous breakdown of a certain symmetry (G triple-over-dot-symmetry). Based on this view, we study a quasi-particle picture, in which the G triple-over-dot-transformation becomes the thermal Bogoliubov transformation.

  • NOISE AND PARTICLE CONDENSATION

    H UMEZAWA, Y YAMANAKA

    PHYSICA A   170 ( 2 ) 291 - 305  1991.01  [Refereed]

     View Summary

    This paper is aimed to clarify the appearance of non-quantum noises in quantum systems in various subjects from a unified viewpoint. Examples taken are the squeezed state in quantum optics, the Hawking radiation around the black hole and thermo field dynamics (TFD) in thermal quantum field theory. Under the use of mathematical formulation of TFD, the origin of noises is traced to the Bogoliubov transformation, i.e., the pair condensation of bare particles in the physical vacua. Detailed analysis of the noise energy reveals a crucial distinction among them: Calling the operator generating the noise energy the noise generator, we find two cases, dynamical and spontaneous, depending on whether the noise generator is part of the Hamiltonian or not. The squeezed state belongs to the former, TFD does to the latter.

  • SYMMETRIES IN STOCHASTIC QUANTIZATION AND ITO-STRATONOVICH RELATED INTERPRETATION

    H NAKAZATO, K OKANO, L SCHULKE, Y YAMANAKA

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

  • THERMODYNAMICS AND QUANTUM-FIELD THEORY

    HARDMAN, I, H UMEZAWA, Y YAMANAKA

    PHYSICS LETTERS A   146 ( 6 ) 293 - 298  1990.06  [Refereed]

  • DISSIPATION OF INTERACTING FIELDS IN THE PRESENCE OF BLACK-HOLES

    AEI JOHANSSON, H UMEZAWA, Y YAMANAKA

    CLASSICAL AND QUANTUM GRAVITY   7 ( 3 ) 385 - 390  1990.03  [Refereed]

  • COHERENT AND THERMAL COHERENT STATE

    A MANN, M REVZEN, K NAKAMURA, H UMEZAWA, Y YAMANAKA

    JOURNAL OF MATHEMATICAL PHYSICS   30 ( 12 ) 2883 - 2890  1989.12  [Refereed]

    DOI

    Scopus

    17
    Citation
    (Scopus)
  • RELATION BETWEEN QUANTUM AND THERMAL FLUCTUATIONS

    A MANN, M REVZEN, H UMEZAWA, Y YAMANAKA

    PHYSICS LETTERS A   140 ( 9 ) 475 - 478  1989.10  [Refereed]

  • SELF-CONSISTENT RENORMALIZATION IN THERMOFIELD DYNAMICS

    H UMEZAWA, Y YAMANAKA

    JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL   22 ( 13 ) 2461 - 2473  1989.07  [Refereed]

  • SELF-CONSISTENT ANALYSIS OF A THERMALLY DISSIPATIVE QUANTUM-FIELD SYSTEM - KORENMAN MODEL

    HARDMAN, I, H UMEZAWA, Y YAMANAKA

    PHYSICA A   156 ( 3 ) 853 - 875  1989.04  [Refereed]

  • ONE-LOOP CALCULATION IN TIME-DEPENDENT NON-EQUILIBRIUM THERMO FIELD-DYNAMICS

    H UMEZAWA, Y YAMANAKA

    FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS   37 ( 11 ) 819 - 837  1989  [Refereed]

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • LINEAR RESPONSE IN NON-EQUILIBRIUM THERMO FIELD-DYNAMICS

    K NAKAMURA, Y YAMANAKA, H UMEZAWA

    PHYSICA A   152 ( 1-2 ) 29 - 50  1988.09  [Refereed]

  • MICRO, MACRO AND THERMAL CONCEPTS IN QUANTUM-FIELD THEORY

    H UMEZAWA, Y YAMANAKA

    ADVANCES IN PHYSICS   37 ( 5 ) 531 - 557  1988.09  [Refereed]

    DOI

    Scopus

    75
    Citation
    (Scopus)
  • CALCULATION OF BETA-FUNCTIONS UP TO 2-LOOP ORDER IN PHI-4 THEORY BASED ON STOCHASTIC QUANTIZATION METHOD

    H NAKAZATO, G TAKADA, H SOSHI, Y YAMANAKA

    PROGRESS OF THEORETICAL PHYSICS   80 ( 3 ) 559 - 565  1988.09  [Refereed]

    DOI

  • SPATIALLY INHOMOGENEOUS THERMO FIELD-DYNAMICS

    K NAKAMURA, H UMEZAWA, Y YAMANAKA

    PHYSICA A   150 ( 1 ) 118 - 136  1988.05  [Refereed]

  • SPONTANEOUS CREATION OF DISSIPATION IN THERMO FIELD-DYNAMICS AND ITS EXAMPLES

    T ARIMITSU, H UMEZAWA, Y YAMANAKA, NJ PAPASTAMATIOU

    PHYSICA A   148 ( 1-2 ) 27 - 45  1988.02  [Refereed]

  • TIME-DEPENDENT CANONICAL FORMALISM OF THERMALLY DISSIPATIVE FIELDS AND RENORMALIZATION SCHEME

    HARDMAN, I, H UMEZAWA, Y YAMANAKA

    JOURNAL OF MATHEMATICAL PHYSICS   28 ( 12 ) 2925 - 2938  1987.12  [Refereed]

    DOI

    Scopus

    30
    Citation
    (Scopus)
  • CANONICAL FORMALISM OF DISSIPATIVE FIELDS IN THERMO FIELD-DYNAMICS

    T ARIMITSU, H UMEZAWA, Y YAMANAKA

    JOURNAL OF MATHEMATICAL PHYSICS   28 ( 11 ) 2741 - 2752  1987.11  [Refereed]

    DOI

    Scopus

    33
    Citation
    (Scopus)
  • The Thermally Dissipative Free Field and Canonical Formalism

    H., Umezawa, Y., Yamanaka, I., Hardman, T., Arimitsu

    Wondering in the Fields     174-190  1987.01  [Refereed]

  • MINKOWSKI STOCHASTIC QUANTIZATION

    H NAKAZATO, Y YAMANAKA

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

    DOI

    Scopus

    26
    Citation
    (Scopus)
  • COMPLETE RENORMALIZATION SCHEME FOR FICTITIOUS-TIME CORRELATIONS IN STOCHASTIC QUANTIZATION METHOD BASED ON OPERATOR-FORMALISM

    M NAMIKI, Y YAMANAKA

    PROGRESS OF THEORETICAL PHYSICS   75 ( 6 ) 1447 - 1459  1986.06  [Refereed]

    DOI

  • POSSIBLE NONVANISHING MASS OF PHOTON

    H NAKAZATO, M NAMIKI, Y YAMANAKA, K YOKOYAMA

    PROGRESS OF THEORETICAL PHYSICS   75 ( 3 ) 686 - 691  1986.03  [Refereed]

    DOI

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

    H NAKAZATO, M NAMIKI, Y YAMANAKA, K YOKOYAMA

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

    DOI

  • SELF-REGULARIZED FIELD-THEORY AND ITS RENORMALIZATION IN MODIFIED STOCHASTIC QUANTIZATION

    M NAMIKI, Y YAMANAKA

    HADRONIC JOURNAL   7 ( 3 ) 594 - 640  1984  [Refereed]

  • NEUTRINO MASSES, MIXING, AND OSCILLATIONS IN THE S4 MODEL OF PERMUTATION SYMMETRY

    T BROWN, S PAKVASA, H SUGAWARA, Y YAMANAKA

    PHYSICAL REVIEW D   30 ( 1 ) 255 - 257  1984  [Refereed]

    DOI

    Scopus

    53
    Citation
    (Scopus)
  • PHENOMENOLOGICAL ANALYSIS OF Z0-]LL-GAMMA DECAY ON EXCITED LEPTON HYPOTHESIS

    H NAKAZATO, M NAMIKI, Y YAMANAKA, K YOKOYAMA

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

    DOI

  • STOCHASTIC QUANTIZATION OF NON-ABELIAN GAUGE FIELD - UNITARITY PROBLEM AND FADDEEV-POPOV GHOST EFFECTS

    M NAMIKI, OHBA, I, K OKANO, Y YAMANAKA

    PROGRESS OF THEORETICAL PHYSICS   69 ( 5 ) 1580 - 1599  1983  [Refereed]

    DOI

  • STOCHASTIC QUANTIZATION METHOD OF FERMION FIELDS

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

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

    DOI

  • STOCHASTIC QUANTIZATION METHOD IN OPERATOR-FORMALISM

    M NAMIKI, Y YAMANAKA

    PROGRESS OF THEORETICAL PHYSICS   69 ( 6 ) 1764 - 1793  1983  [Refereed]

    DOI

  • B-L AND NUCLEON DECAYS IN THE SUBQUARK MODEL

    OHBA, I, Y YAMANAKA

    PHYSICS LETTERS B   109 ( 5 ) 375 - 379  1982  [Refereed]

  • PERMUTATION SYMMETRIES AND THE FERMION MASS MATRIX

    Y YAMANAKA, H SUGAWARA, S PAKVASA

    PHYSICAL REVIEW D   25 ( 7 ) 1895 - 1903  1982  [Refereed]

    DOI

    Scopus

    176
    Citation
    (Scopus)
  • HIGH-ENERGY MANIFESTATIONS OF HEAVY QUARKS IN AXIAL-VECTOR NEUTRAL CURRENTS

    Y KIZUKURI, OHBA, I, K OKANO, Y YAMANAKA

    PHYSICAL REVIEW D   23 ( 9 ) 2095 - 2097  1981  [Refereed]

    DOI

    Scopus

    6
    Citation
    (Scopus)
  • e+e- decay processes of cbar c bound states in relativistic harmonic oscillator model

    Y. Kizukuri, K. Okano, Y. Yamanaka

    Prog. Theor. Phys.   59   949 - 958  1978  [Refereed]

    DOI

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Books and Other Publications

  • 「複雑系叢書 5 複雑さと法則」 「量子揺らぎ」

    早稲田大学複雑系高等研究所

    共立出版  2006.11

  • ペレス 量子論の概念と手法

    大場一郎, 山中由也, 中里弘道

    丸善  2001.09

  • Selected Papers of Hiroomi Umezawa

    A. Arimitsu, H. Ezawa, H. Matsumoto, K. Nakamura, Y. Yamanaka

    学習院大  2001.07

Research Projects

  • 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

    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

     View Summary

    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

     View Summary

    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

  • Quantum transport equation snd its application to ultracold atomic system

    Project Year :

    2013
    -
    2015
     

     View Summary

    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

  • Formulation of Bose-Einstein condensation of neutral atoms based on thermal field theory

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

    Project Year :

    2005
    -
    2008
     

    YAMANAKA Yoshiya, OKUMURA Masahiko, MINE Makoto, KOBAYASHI Keita

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

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

    Project Year :

    2001
    -
    2006
     

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

     View Summary

    In this project the head investigator, I. Ohba together with Y. Ota quantized the dissipative chaos system applying the method of stochastic state diffusion, and discussed the quantum-classical correspondence quantitatively calculating pseudo-Lyapunov index. Then they developed the semiclassical approximation on the quantum dissipative system. Further, they focused on the quantum computer of nuclear spins in a semiconductor proposed by B. E. Kane, and solved the time-dependent Schrodinger equation rigorously and showed that the inevitable operation error exists in the previously proposed way of construction of the quantum gates.H. Nakazato and K. Yuasa reconsidered the quantum Zeno effect including the degrees of freedom of the environment, and found that the "environment" (of finite degrees of freedom)is purified by the Zeno-like measurement in which the frequent sequential measurements are performed on the system. As an application, they showed that the entanglement distillation and initialization of qubits are possible. Further, they developed the method to derive the solution of Lindlbad master equation with the Kraus representation.Y. Yamanaka together with one of the members M. Okumura considered the system of Bose-Einstein condensation of atomic gas where the translational invariance is absent due to the trapping potential for atoms, and developed its quantum field theoretical formulation. They also showed that inclusion of Goldstone mode is essential in this framework. Particularly, this formulation keeps the Ward-Takahashi identities and the degenerated vacuum is orthogonal to each other.Y. Yamanaka, M. Okumura and M. Mine showed the relation between two kinds of field theoretical methods in which the Goldstone mode is taken care of for a trapped Bose-condensed system. Further, they formulated the method in which the effect of the zero-mode on the response of trapped Bose-Einstein condensates against the external perturbation at finite temperature can be evaluated. Using this formalism, they numerically calculated its effects

  • Nelsonの量子力学に基づくトンネリング時間及びその周辺の研究

    日本学術振興会  科学研究費助成事業

    Project Year :

    1997
     
     
     

    大場 一郎, 山中 由也, 栗原 進

     View Summary

    本課題研究における平成9年度の各項目に対する研究成果は以下の通りであり,雑誌論文として出版された.
    (1)熱浴との結合系に関しては,一般的にいえば,Feynman-VernonやCaldeira-Leggettによる方法が知られている.ここではf(t)を任意の既知正関数として(例えばe^<2γt>)、作用を S=∫dt[m/2x^2+V(x)]f(t)とおけば,この系は正準形式を満たす.しかも,得られるEuler方程式は散逸型mx+2mγx+(∂v)/(∂x)=0となる.この枠組みを用いて,散逸系における量子化を正準形式と経路積分法において実行することに成功し,その実効的schrodinger方程式に対応するNelson量子力学を定式化,基礎方程式であるLangevin方程式を書き下すことができた.現在,種々のモデルについてシミュレーションを実行,その物理的内容の分析が進行中である.
    (2)Nelsonの量子力学を多チャンネルに拡張し,トンネル時間に現れる非弾性効果を評価することに成功した.従来までのNelsonの量子力学では一つのチャンネルのみを扱い,その中での確率過程であった.ここでは別のチャンネルに量子飛躍する.それを表すために,対応するLangevin方程式に新たな項を導入してNelson量子力学の枠組みを拡張し,この効果を取り入れることに成功した.
    (3)引力フェルミ系の集団励起スペクトルを計算し,phonon-roton的分散関係を,またBE凝縮体から結晶への量子転移について示唆的な結果を得た.そしてリング状超流体の永久流減衰をroton励起を伴う位相場のトンネル現象としての記述を試みている.さらに,引力フェルミ系の新しい基底状態-supersolid-の可能性を変分波動関数を用いて示した.また,SIS接合に新しい赤外発散効果が存在することを予言した.

  • Nelsonの量子力学に基づくトンネリング時間の研究

    日本学術振興会  科学研究費助成事業

    Project Year :

    1996
     
     
     

    大場 一郎, 山中 由也

     View Summary

    本研究で用いたNelsonの量子力学は従来のコペンハーゲン的解釈を量子揺らぎを伴う拡散過程で置き換えた。その確立微分方程式は粒子の一つ一つの軌跡の時間発展を与え、その経路のアンサンブルが量子力学的振る舞いを再現する。私たちはこのアンサンブルで、実験室で測定されるトンネル時間を評価することを提案している。
    本年度は、(i)Nelsonの量子力学を多チャンネルに拡張し、トンネル時間に現れる非弾性効果を評価することに成功した。従来までのNelsonの量子力学では一つのチャンネルのみを扱い、その中での確率過程であった。ここでは別のチャンネルに量子飛躍する。それを表すために、対応するLangevin方程式に新たな項を導入してNelson量子力学を枠組みを拡張し、この効果を取り入れることに成功した。その結果は大阪とボンベイにおける2つの国際会議、日本物理学会で講演し、Phys.Rev.Aに投稿した本論文は受理され、近々出版の予定である。
    また、(ii)熱浴との結合系に関しては、一般的にいえば、Feynman-VernonやCaldeira-Leggettによる方法が知られている。ここで∫(t)を任意の既知正関数として(例えば、e^<2γt>)、作用を S=∫dt[m/2x^・^2+V(x)]∫(t)とおけば、この系は正準形式を満たす。しかも、得られるEuler方程式は散逸型mx^^‥+2mγx^^・+(∂v)/(∂x)=0となる。従って、この枠組みを用いて、散逸系における量子化を正準形式と経路積分法において実行することに成功し、その実効的Schr^^odinger方程式に対応するNelsonの量子力学を定式化、基礎方程式であるLangevin方程式を書き下すことができた。現在、障壁や共鳴量子井戸における通過時間、滞在時間に関するシミュレーションを遂行中である。これらの初歩的な結果は、3月の金沢大学における本重点領域研究の研究会、名城大学における物理学会で発表することになっている。

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Misc

  • 7aAW-2 Analysis of Quantum Transport Equation for Nonequilibrium Process in Ultracold Two-component Fermionic Gases

    Imai Ryosukc, Nakamura Yusuke, Kuwahara Yukiro, Yamanaka Yoshiya

    Meeting abstracts of the Physical Society of Japan   69 ( 2 ) 53 - 53  2014.08

    CiNii

  • 8aAW-12 Analysis on zero mode and phase fluc