研究者業績

田﨑 晴明

タザキ ハルアキ  (Hal Tasaki)

基本情報

所属
学習院大学 理学部 物理学科 教授
学位
理学博士

J-GLOBAL ID
201301011914383202
researchmap会員ID
7000005963

外部リンク

MISC

 115
  • Sheldon Goldstein, Takashi Hara, Hal Tasaki
    PHYSICAL REVIEW LETTERS 111(14) 2013年10月  
    We prove two theorems concerning the time evolution in general isolated quantum systems. The theorems are relevant to the issue of the time scale in the approach to equilibrium. The first theorem shows that there can be pathological situations in which the relaxation takes an extraordinarily long time, while the second theorem shows that one can always choose an equilibrium subspace, the relaxation to which requires only a short time for any initial state.
  • Hal Tasaki
    PHYSICAL REVIEW LETTERS 110(23) 2013年6月  
    In a system of interacting f = 1 bosons (in the subspace where the total spin in the z direction is vanishing), we prove inequalities for the ground state expectation value of the density of spin-0 bosons. The inequalities imply that the ground state possesses "polar" or "antiferromagnetic" order when the quadratic Zeeman term q is large enough. In the low density limit, the inequalities establish the existence of a sharp transition at q = 0 when q is varied.
  • Hosho Katsura, Hal Tasaki
    PHYSICAL REVIEW LETTERS 110(13) 2013年3月  
    We prove basic theorems about the ground states of the S = 1 Bose-Hubbard model. The results are quite universal and depend only on the coefficient U-2 of the spin-dependent interaction. We show that the ground state exhibits saturated ferromagnetism if U-2 < 0, is spin-singlet if U-2 > 0, and exhibits "SU(3)-ferromagnetism" if U-2 = 0, and completely determine the degeneracy in each region. DOI: 10.1103/PhysRevLett.110.130405
  • Keiji Saito, Hal Tasaki
    JOURNAL OF STATISTICAL PHYSICS 145(5) 1275-1290 2011年12月  
    Recently, in their attempt to construct steady state thermodynamics (SST), Komatsu, Nakagawa, Sasa, and Tasaki found an extension of the Clausius relation to nonequilibrium steady states in classical stochastic processes. Here we derive a quantum mechanical version of the extended Clausius relation. We consider a small system of interest attached to large systems which play the role of heat baths. By only using the genuine quantum dynamics, we realize a heat conducting nonequilibrium steady state in the small system. We study the response of the steady state when the parameters of the system are changed abruptly, and show that the extended Clausius relation, in which "heat" is replaced by the "excess heat", is valid when the temperature difference is small. Moreover we show that the entropy that appears in the relation is similar to von Neumann entropy but has an extra symmetrization with respect to time-reversal. We believe that the present work opens a new possibility in the study of nonequilibrium phenomena in quantum systems, and also confirms the robustness of the approach by Komatsu et al.
  • Yohei Morikuni, Hal Tasaki
    JOURNAL OF STATISTICAL PHYSICS 143(1) 1-10 2011年4月  
    We consider a (small) quantum mechanical system which is operated by an external agent, who changes the Hamiltonian of the system according to a fixed scenario. In particular we assume that the agent (who may be called a demon) performs measurement followed by feedback, i.e., it makes a measurement of the system and changes the protocol according to the outcome. We extend to this setting the generalized Jarzynski relations, recently derived by Sagawa and Ueda for classical systems with feedback. One of the two relations by Sagawa and Ueda is derived here in error-free quantum processes, while the other is derived only when the measurement process involves classical errors. The first relation leads to a second law which takes into account the efficiency of the feedback.

書籍等出版物

 6

講演・口頭発表等

 4

共同研究・競争的資金等の研究課題

 1