Department of Physics, The University of Tokyo
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2010 seminars

Schedule of winter semester (start from 13:00 @ #933)

Oct. 7 Takahiro Sagawa (Ueda absent)
Oct. 14 Shuta Nakajima (Kawaguchi absent)
Oct. 21 (skip, Ueda and Kawaguchi absent)
Oct. 28 Shun Uchino (Otsuka group in Univ. of Tokyo)
Nov. 2 Masatoshi Sato (ISSP)
Nov. 4 (skip, move to Nov. 2)
Nov. 11 Naoyuki Sakumichi (Kawaguchi absent)
Nov. 18 Yu Watanabe
Nov. 25 Simone De Liberato
Dec. 2 (skip, Student chapter)
Dec. 9 Yuki Kawaguchi (Ueda absent)
Dec. 16 Pascal Naidon(Ueda absent)
Dec. 23 (skip, National holiday)
Dec. 30 (skip, winter vacation)
Jan. 6 (skip, move to Jan.13)
Jan. 12 Shimpei Endo
Jan. 20 Nguyen Thanh Phuc
Jan. 27 Hideki Yamaguchi
Feb. 1 Susumu Okazawa (KEK)
Feb. 3 Masahiro Takahashi
Feb. 10 Shingo Kobayashi
Feb. 17 Tatsuhiko Ikeda
Feb. 24 Yui Kuramochi
Mar. 3 Takehiro Deguchi and Yuya Tanizaki
Mar. 10 Guest
Mar. 17 Guest
Mar. 24 (skip, Mar. 25-28 JPS meeting)


2010/10/7(Thu) 13:00
speaker Takahiro Sagawa
title Information Thermodynamics in Small Systems
abstract Due to the recent technologies of manipulating nonequilibrium systems at nano and micro scales such as biological molecular motors, stochastic aspects of thermodynamics have been more and more important in terms of experiments as well as theories of nonequilibrium statistical mechanics. In this seminar, I would like to talk about thermodynamics of nonequilibrium information processing, which leads us to the foundations of thermodynamics and statistical mechanics with the assistance of the celebrated "Maxwell's daemon." Starting with a short introduction of basic concepts of information theory, I will talk about general theory of "information thermodynamics," in particular its second law and the generalized Jarzynski equality. I will also talk about a recent experiment that realized Szilard-type information-heat engine for the first time, and also verified the generalized Jarzynski equality.

2010/10/14(Thu) 13:00
speaker Shuta Nakajima
title Measurement of an Efimov trimer binding energy in a three-component mixture of 6Li
abstract Recently, T. Lompe et.al. demonstrated a radio-frequency (RF) association of an Efimov trimer state in a three-component mixture of 6Li atoms. This method provides a way to determine the binding energy of the Efimov trimers not only at particular points, but also in a continuous range of magnetic field. In this talk, I will talk about our recent measurement of the binding energy of the Efimov states in the three-component mixture of 6Li atoms via "Atom-dimer loss measurement" and "RF association". In the latter experiment, We precisely measured the binding energy of an Efimov state by RF association over a range of magnetic field of 50 G. We performed the spectroscopy at various temperatures and confirmed that the lowest temperature condition in our experiment does not suffer from any finite-temperature shift in the spectroscopy. The obtained trimer binding energy was found to significantly deviate from our nonuniversal theory prediction based on a three-body parameter with a monotonic energy dependence, and suggests a more complicated variation of the three-body parameter.

2010/10/28(Thu) 13:00
speaker Shun Uchino
title Phase Structure and Low-energy Excitation in Spinor Bose-Einstein Condensates
abstract Based on the theory of weakly interacting Bose gases, I will dicuss phase structure and low-energy excitations in spinor Bose-Einstein condensates. My focus will be on the Lee-Huang-Yang corrections that are the first quantum corrections of physical quantities, and on the Nambu Goldstone (NG) modes that are the dominant degrees of freedom to determine the low-energy behavior of the system. In connection with the latter focus, it is shown that quasi-NG modes (QNG), which play prominent roles in high-energy physics, emerge in the spin-2 nematic phase. I will delineate the physical significance of the QNG modes.
[1]S. Uchino, M. Kobayashi, M. Ueda, Phys. Rev. A81, 063032(2010)
[2]S. Uchino, M. KObayashi, M. Nitta, M. Ueda, arXiv:10102864

2010/11/2(Tus) 13:00
speaker Masatoshi Sato
title Topological superconductors
abstract Starting from the basic properties of topological phases such as the bulk-edge correspondence, I would like to explain recent topics on topological properties of superconductors. In particular, non-Abelian topological order in noncentrosymmetric superconductors/superfluids and topological phases in spin-triplet(or odd-parity) superconductors are explained.

[1]MS, Bussei Kenkyu 94 (2010) 311.
[2]MS, Phys. Rev. B79, 214526 (2009); Phys. Rev. B81, 220504(R) (2010)
[3]MS, Satoshi Fujimoto, Phys. Rev. B79, 094504 (2009); arXiv.1007.4369, MS, Yoshiro Takahashi, Satoshi Fujimoto, Phys. Rev. Lett. 103, 020401 (2009); arXiv:1006.4487

2010/11/11(Thu) 13:00
speaker Naoyuki Sakumichi
title Quantum cluster expansion study of the BCS-BEC crossover
abstract We address the BCS-BEC crossover in a two-component cold Fermi gas with short-range interaction. To this end, we use the Lee-Yang quantum cluster expansion method, which enables us to expand the logarithm of the grand partition function in a power series of fugacity [1]. We can formally sum up an infinite series of the clusters which are expressed in terms of ladder graphs. The critical fugacity can be defined as the divergent point of the grand partition function for any value of a scattering length. The obtained critical fugacity agrees with the BEC transition fugacity in the BEC limit. And we discuss the critical fugacity at the unitarity limit.

[1] T. D. Lee and C. N. Yang, Phys. Rev. 113, 1165 (1958)

2010/11/18(Thu) 13:00
speaker Yu Watanabe
title Uncertainty Relation Revisited from Quantum Estimation Theory
abstract The uncertainty relation is among the most salient properties of quantum theory, imposing fundamental constraints on precise measurement of non-commutable observables. Thus, there must exist some trade-off relations concerning the information that is obtained by quantum measurements. By invoking quantum estimation theory we formulate the uncertainty relation for arbitrary quantum states and measurements in a finite-dimensional Hilbert space. In general, an estimation process from the measurement outcomes is essential to clarify the trade-off relation of our knowledge obtained by measurement. We introduce a measurement error that involves such estimation processes. We derive the trade-off relation of the measurement errors of two observables such that the bound is achievable for all quantum states and observables. In particular, we find the tightest ever bound that is achievable for all quantum states and observables.
Yu Watanabe, Takahiro Sagawa, and Masahito Ueda, arXiv:1010.3571 (2010).

2010/11/25(Thu) 13:00
speaker Simone De Liberato
title Carnot's Theorem for nonequilibrium reservoirs
abstract Carnot's theorem poses a fundamental limit on the maximum efficiency achievable from an engine that works between two reservoirs at thermal equilibrium. In this talk I will show how it is possible to extend this result to the case of arbitrary nonequilibrium and even quantum coherent reservoirs by proving that a single nonequilibrium reservoir is formally equivalent to multiple equilibrium ones. In order to show an application of such theorem I will discuss the possibility of realizing an engine powered by quantum coherence that works at unit efficiency.

S. De Liberato and M. Ueda arXiv:1007.0335

2010/12/9(Thu) 13:00
speaker Yuki Kawaguchi
title Spontaneous Magnetic Ordering in a Ferromagnetic Spinor Dipolar Bose-Einstein Condensate
abstract We study the spin dynamics of a spin-1 ferromagnetic Bose-Einstein condensate with magnetic dipole-dipole interaction (MDDI) based on the Gross-Pitaevskii and Bogoliubov theories. We find that various magnetic structures such as checkerboards and stripes emerge in the course of the dynamics due to the combined effects of spin-exchange interaction, MDDI, quadratic Zeeman and finite-size effects, and nonstationary initial conditions. However, the short-range magnetic order observed by the Berkeley group [Phys. Rev. Lett. 100, 170403 (2008)] is not fully reproduced in our calculations; the periodicity of the order differs by a factor of 3 and the checkerboard pattern eventually dissolves in the course of time. Possible reasons for the discrepancy are discussed.

YK, Saito, Kudo, and Ueda, PRA 82, 043627 (2010).

2010/12/16(Thu) 13:00
speaker Pascal Naidon
title The physics of 3-component gas of lithium 6
abstract This seminar will review our current understanding of the physics of ultracold gases of lithium 6 atoms that are prepared in 3 different internal spin states. When an external magnetic field is applied to these systems, the scattering lengths between the atoms become very large, and the physics acquires some universal character. In particular, 3 atoms in different spin states can bind together according to a universal mechanism called the Efimov effect. Various indirect signatures and first-time direct spectroscopy of these 3-body bound states have been demonstrated in recent experiments. These results are essentially consistent with the universal Efimov effect, but non-universal deviations remain to be understood.

2010/1/12(Wed) 13:00 @445
speaker Shimpei Endo
title Many-body effects of BEC-BCS crossover in an ultracold Fermi gas.
abstract The study of the BEC-BCS crossover has a long history, and various kinds of many-body techniques have been applied. However, there still remains some controversies on the topic. One reasons is that it is important but technically difficult to incorporate three-body and four-body correlations into thermodynamic calculations. Thus, it is nice if we have some ways to incorporate the effect of three-body correlations in a simple manner. In this seminar, I propose an approximate way to solve three-body problem in the vacuum for a two component Fermi system, which may be able to be naturally incorporated in a thermodynamic calculations to include the effect of the atom-dimer collision. It turns out that it predicts the atom-dimer scattering length 1.08, which is close to the exact value 1.18. I will discuss some properties of this approximation and some possible future prospects.

2010/1/20(Thu) 13:00
speaker Nguyen Thanh Phuc
title Phase Diagram of a Three-Dimensional Spin-1 Ferromagnetic Condensate under a Quadratic Zeeman Effect
abstract In this seminar, the thermal equilibrium properties of a uniform F=1 Rb87 spinor condensate under a quadratic Zeeman effect are presented. From the finite-temperature phase diagram, obtained by using the Popov approximation, it can be seen that a two-step phase transition occurs, in which the system changes from normal phase to non-magnetized polar phase, and then to BA phase with a finite transverse magnetization. It also turns out that due to the coupling with the condensate, there exists a coherence within the thermal part, and thus it exhibits a finite magnetization. Finally the effects of non-condensed atoms at temperatures near absolute zero in a spinor BEC are investigated by using the expansion of the order parameter with respect to the small non-condensate fraction. The result shows that the Popov approximation breaks down at temperatures near absolute zero, and the ground-state phase diagram is the same as that obtained by neglecting the whole effects of non-condensed atoms, which is a non-trivial result.

2010/1/27(Thu) 13:00
speaker Hideki Yamaguchi
title A nonequilibrium study on molecular motors
abstract Molecular motors have been intensively investigated for around 20 years. They are special proteins that can move unidirectionally using energy gained by consuming "fuel" molecules (ATPs). This property make them actual motors, which are targets of nonequilibrium-statistical studies. In this seminar, nonequilibrium properties of molecular motors revealed by experiments are reviewed, with theoretical analyses. This seminar is divided into two parts: in the former part, I review two experiments. One is on the ratio of realization probability of forward/backward movements, and the other is on dwell time (interval between two successive movements). These two data are considerd theoretically in the latter part.

2010/2/1(Tue) 13:00 @1320
speaker Susumu Okazawa
title Black Holes and the Fluctuation Theorem
abstract We investigate non-equilibrium nature of fluctuations of black hole horizons by applying the fluctuation theorem. The theorem reveals a violation of the generalized second law of black hole thermodynamics. In this talk, we explain the derivation of effective equation of motion of matter field and show the fluctuation theorem for black holes and matters in a certain approximation. After that, we introduce a model which imitate an evaporating black hole.

2010/2/3(Thu) 13:00
speaker Masahiro Takahashi
title Vortex State in Bose-Einstein Condensates with Finite-Range Interactions
abstract We investigate the vortex nature of Bose-Einstein condensates (BECs) with finite-range interactions. The interparticle interaction is described by contact interaction in ordinary BECs. However, by introducing Raman-coupled Rydberg atoms with the large detuned lasers, BECs with finite-range interaction can be realized[1]. In such systems, the ground-state density profile will be significantly changed to periodically oscillating one. We introduce how such system is realized by lasers, and how vortex states will be affected by spatially modulated density. This presentation is based on the results of numerical calculation of the Gross-Pitaevskii and Bogoliubov-de Gennes equations derived by mean field approximation.
[1] N. Henkel, R. Nath, and T. Pohl, Phys. Rev. Lett. 104, 195302 (2010).

2010/2/10(Thu) 17:00
speaker Shingo Kobayashi
title Selection rule of Topological Excitations in Spin-1 BECs
abstract We have already known that spinar Bose-Einstein Condensates accommodate many kind of topological excitations due to a lot of internal degree of freedoms. These topological excitations are defined for each order phases independently. In this talk, we try to realize the connection between topological exctations for different phases in spin-1 BECs.Our calculation is based on a homotopy exact sequence and a mathematical model.

2010/2/17(Thu) 13:00
speaker Tatsuhiko Ikeda
title An approach to establish the foundation of statistical mechanics
abstract The foundation of statistical mechanics has long been unclear. Recently, the problem is being studied on so-called eigenstate thermalization hypothesis(ERH). I will talk about our approach based on a new hypothesis we call eigenstate randomization hypothesis(ERH).
Reference: T. N. Ikeda, Y. Watanabe, and M. Ueda, arXiv:1012.3237

2010/2/24(Thu) 13:00
speaker Yui Kuramochi
title Continuous Measurement on a Particle in 1-Dimensional Optical Lattices
abstract In this seminar, my study on the continuous position measurement process on a paricle in 1-dimensional lattices is reported. According to previous works on a continuous position measurement on a particle in free 1-dimensional space, with any initial condition, the distribution of the quantum states goes to stational one in which all the wave functions are Gaussian with fixed second order momments. We consider a similar measurement process on a particle in 1-dimensional lattice where the position operator takes discrete values. Numerical analysis shows that stational distribution of the position dispersion is not simply peaked, while in continuous case it is accumulated in a single value. The physical origins of such behaviors are not fully understood.

2010/3/3(Thu) 13:00
speaker Takehiro Deguchi
title New approach to classical statistical mechanics
abstract The ordinal way to explain classical statistical mechanics is based on the idea of number of states and Boltzmann entropy. But if we take that way, the relationship to thermodynamics or information theory becomes unclear. In this seminar, I offer the one based on heat, work and conditions about temperature, which can solve these issues.
speaker Yuya Tanizaki
title The scattering between the 3-particle bound state and the atom
abstract As is well known, two heavy fermions and one another kind of fermion can form a Efimov trimer if the mass ratio is larger than about 13.6. Recently, Kartavtev and Malykh have shown that for the smaller mass ratio > 8.17 the three-body bound state exists. I will talk about the scattering problem between the trimer and the atom using the AGS equation, which describes the scattering amplitude for the four-prticle collision process.

Schedule of summer semester (start from 13:00 @ #933)
Apr. 15(Thu) Takahiro Sagawa
    "On the generators of quantum dynamical semigroups"
    G. Lindblad, Commun. Math. Phys. 48, 119-130 (1976).

Apr. 19(Mon) #933 13:00-
speaker Prof. P. Blair Blakie (Otago University)
title Dynamics and statistical mechanics of ultra-cold Bose gases using c-field techniques
abstract I will discuss phase space techniques based on the Wigner representation that provide an approximate description of dilute ultra-cold Bose gases. In this approach the quantum field evolution can be represented using equations of motion of a similar form to the Gross-Pitaevskii equation but with stochastic modifications that include quantum effects in a controlled degree of approximation. These techniques provide a practical quantitative description of both equilibrium and dynamical properties of Bose gas systems. We develop versions of the formalism appropriate to zero temperature, where quantum fluctuations can be important, and at finite temperature where thermal fluctuations dominate. Applications to a wide range of phenomena will be discussed.

Apr. 22(Thu) Yu Watanabe
    "Monotone metrics on matrix spaces"
    Dénes Petz, Linear Algebra and its Applications. 244,(1996), Page 81-96.
        1, 2, 3, 4, 5, 6, 7, 8, 9.

May. 6(Thu) Shingo Kobayashi
    "Quantum Spin Hall Effect and Topological Phase Transition in HgTe Quantum Wells"
    B. Andrei Berneving, Taylor L. Hughes, Shou-Cheng Zhang, Science 314, (2006), 1757

May. 13(Thu) 15:00- Tatsuhiko Ikeda
    "Nonequilibrium Equality for Free Energy Differences"
   C. Jarzynski, Phys. Rev. Lett.78 , (1997) 2690

    "Equilibrium free-energy differences from nonequilibrium measurements: A master-equation approach"
   C. Jarzynski, Phys. Rev. E 56, (1997) 5018

May. 17(Mon) #445 Yui Kuramochi
    "Time in the Quantum Theory and the Uncertainty Relation for Time and Energy"
    Y. Aharanov and D. Bohm, Phys. Rev. 122, (1961) 1649

May. 24(Mon) 15:00- #445 Naoyuki Sakumichi
    "Confinement of quarks"
    Kenneth G. Wilson , Phys. Rev. D, 10 (1974) 2445

Jun. 4(Fri) Yusuke Endo
    "Off-Diagonal Long-Range Order in Solids"
    Hirotsugu Matsuda and Toshihiko Tsuneto, Prog. Theor. Phys. Suppl. 46, (1970) 411-436

Jun. 17(Thu) Naoki Hiratani
    "Proof of the Ergodic Theorem and the H-Theorem in Quantum Mechanics"
    John von Neumann, arXiv:1003.2133v1

Jun. 24(Thu) Ken Huno
    "Particle creation by black holes "
    S. W. Hawking, Communication in Mathematical Physics, 43 , (1975) 199

Jul. 1(Thu) Shimpei Endo
    "A quantum gas microscope for detecting single atoms in a Hubbard-regime optical lattice"
   Waseem S. Bakr, Jonathon I.Gillen, Amy Peng, Simon Fölling and Markus Greiner, Nature, 462 (2009) 74

    "In situ observation of incompressible Mott-insulating domains in ultracold atomic gases"
   Nathan Gemelke, Xibo Zhang, Chen-Lung Hung and Cheng Chin, Nature, 460 (2009) 995

    "Probing the Superfluid-Mott-Insulator Transition at the Single-Atom Level"
   W. S. Bakr, A. Peng, M. E. Tai, R. Ma, J. Simon, J. I. Gillen, S. Fölling, L. Pollet, and M. Greiner, 10.1126/science.1192368, Science Express Reports (2010)

Jul. 8(Thu) Nguyen Thanh Phuc
    "Ordering, metastability and phase transitions in two-dimensional systems"
   J. M. Kosterlitz and D. J. Thouless, J. Phys. C, 6, (1973) 1181

    "Universal Jump in the Superfluid Density of Two-Dimensional Superfluids"
    David R. Nelson and J. M. Kosterlitz, Phys. Rev. Lett, 39, (1977) 1201

Jul. 15(Thu) 12:00- Hideki Yamaguchi
    "Steady-State Thermodynamics of Langevin Systems"
    Takahiro Hatano and Shin-ichi Sasa, Phys. Rev. Lett 86, (2001 )3463

    "Integral fluctuation theorem for the housekeeping heat "
    T. Speck and U. Seifert , J. Phys. A 38, (2005)L581