Department of Physics, The University of Tokyo
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2009 seminars

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

Oct. 6   Michikazu Kobayashi
Oct. 20 Peng Zhang
Oct. 27 Pascal Naidon
Nov. 10 Sang Wook Kim
Nov. 24 Yu Watanabe
Dec. 1   Shingo Kobayashi
Dec. 8   Yuki Kawaguchi
Dec. 15 Shuta Nakajima
Dec. 22 Takahiro Sagawa
Jan. 6   Prof. Daw-Wei Wang(start from 13:30 @ #233)
Jan. 12 Shimpei Endo
Jan. 19 Nguyen Thanh Phuc
Jan. 26 Hideki Yamaguchi
Feb. 9   Sousuke Ito, Kyogo Kawaguchi, and Tomoya Hayata
Mar. 2   Masahiro Takahashi (Okayama University)


2009/10/6(Tue) 13:00
speaker Michikazu Kobayashi
title Vortex tiling in spinor Bose-Einstein condensate
abstract Vortex tiling is one of the non-trivial phenomena for vortices in spin-2 spinor Bose-Einstein condensates (BECs) which never happen in spin-1 BECs. According to commensurability between different symmetries of the order parameters inside and outside of a vortex core, the rotational symmetry of the core is spontaneously broken, associating unconventional excitations such as twiston, vorton, and so on. Vortex tiling also enables us to observe the cyclic order parameter in a rotating spin-2 87Rb BEC, regardless of whether its ground state is cyclic or otherwise.

2009/10/20(Tue) 13:00
speaker Peng Zhang
title The two-body Feshbach resonance and theree-body Feshbach resonance in cold atom physics
abstract Two-body Feshbach resonance is a powerful technique in the research of cold atom physics. So far many kinds of Feshbach resonance have been widely used in the in the theoretical and experimental studies. However, in the references the mechanisms of these resonances are described quite differently by different authors. In this talk, based on the multi-channel Lippmman-Schwinger equation, I will show the unified theory for all kinds of two-body Feshbach resonance in cold atom physics. Based on this framework, I show our recent researches on the control of different scattering lengths in the mulit-component quantum gases, and the high-partial wave Feshabch resonances. We further generalize the two-body Feshbach resonance to the three-body case, and discuss the relevant effects on the three-body scattering and losses.

2009/10/27(Tue) 13:00
speaker Pascal Naidon
title Everything you always wanted to know about Efimov states but were afraid to ask
abstract In this seminar I will introduce you to Efimov physics and present the latest experimental and theoretical developments.

2009/11/10(Tue) 13:00
speaker Sang Wook Kim
title Coherence of BECs
abstract In this talk I will review the coherence properties of BECs, which is an old question on the phase standard of macroscopic quantum objects. In fact, this problem is also closely related to the "quantum" Szillard engine. Because it is still an on-going project, I will try to deliver main ideas and basic concepts. I will begin with briefly introducing other current research topics of mine.

2009/11/24(Tue) 13:00
speaker Yu Watanabe
title Uncertainty Relation and Quantum Estimation Theory
abstract To understand Heisenberg's uncertainty relation correctly, it is important to consider how to calculate the estimated value of what we want to know (e.g. position, momentum, etc.) from the measurement outcomes, and how precise and accurate the estimated value is. The quantum estimation theory gives us the best strategy to calculate the estimated value from the measurement outcomes, which is called maximum likelihood estimator. The theory also gives us the precision of the estimator and its lower bound. However the precision of the estimators of non-commutable observables can not achieve their lower bound simultaneously. The trade-off relation between these precision has not found yet.
In this talk I will review some uncertainty relations and quantum estimation theory, and introduce my future plan to find the trade-off relation.

2009/12/1(Tue) 13:00
speaker Shingo Kobayashi
title Relation between topological excitations in spin-1 BECs
abstract In this presentation, I talk about the relationship between different type of topological excitations. Topological excitations are characterized by the degree of mapping, which is known as a topological charge. I show the change of a topological charge which occur as a result of influence of different topological excitations. Especially, I introduce these effects in spinor Bose-Einstein Condensates since they have internal degree of freedoms abundantly.

2009/12/8(Tue) 13:00
speaker Yuki Kawaguchi
title Symmetry classification of the ground states of spinor BECs
abstract The ground state of a spinor BEC is obtained by minimizing the interaction energy. When the spin degrees of freedom is large, however, it is quite complicated to solve the simultaneous equations. In this talk, I will explain the group theoretical method to find the ground state phase of a spinor BEC, which is used to find a ground state of superfluid Helium-3, and p-wave and d-wave superconductors, and show the results for the case of spin-2 and spin-3 spinor BEC.

2009/12/15(Tue) 13:00
speaker Shuta Nakajima
title Loss features in ultracold three component mixtures of 6Li atoms
abstract Last year, an unexpected magnetic field dependence of atomic loss feature was discovered in three component mixtures of 6Li. Since the first report of this loss feature, there has been an increasing interest to the loss mechanism in the context of the trimer formation. We are investigating the relation between the loss features and three-body physics (Efimov physics). Especially,we are interested in confirming the existence of three-body bound state (Efimov state) and observing the enhancement of the loss in the atom-dimer mixture. In our experiments, we made a balanced mixture of the three lowest-lying hyperfine states of 6Li atoms. We confirmed that all three states were lost at 130 G simultaneously. And we also made atom-dimer mixtures by using addiabatic rapid passage and magnetic field sweep. We are now trying to observe the enhancement of the atom-dimer collisions due to the existence of the Efimov states. In this talk, I will talk about details of our experimental schemes and recent results.

2009/12/22(Tue) 13:00
speaker Takahiro Sagawa
title Controlling Fluctuations
abstract   Recent advances of the technology enable us to control the fluctuations of small thermodynamic systems beyond the second law of thermodynamics so that we can be a Maxwell's demon.
  In this talk, I'd like to talk about a recent theoretical result concerning nonequilibrium feedback control: a generalized Jarzynski equality. The conventional Jarzynski equality, which was found in 1997, is one of the most fundamental result in nonequilibrium statistical mechanics, and the equality has been believed to be valid for all isothermal dynamics with the initial canonical distribution. However, in the presence of feedback control, the Jarzynski equality can indeed be violated and should be replaced by a generalized equality which involves the additional term of feedback efficacy.
  The generalized equality can be directly verified by experiments with small thermodynamic systems; in fact, I'd like to talk about the recent experiments in Chuo University, which have realized the "information-energy conversion" driven by a Maxwell's demon, and have verified the generalized Jarzynski equality.

2010/1/6(Wed) 13:30 @ 233, ERATO strategic seminar
speaker Prof. Daw-Wei Wang (National Tsing-Hua University, Hsinchu, Taiwan)
title Itinerant ferro-electricity in the systems of polar molecules
abstract Compared to magnetic dipolar atoms, cold polar molecules are known to have much stronger interaction and has been a promising candidate for a good strongly interacting system. However, the itinerant ferro-electricity of polar molecules are not easily prepared because the rotational degree of freedom of a molecule is quiet different from a true spin. In this talk I will present two different proposals for observing itinerant ferro-electricity in the systems of cold polar molecules. One is by loading fermionic molecules in a 1D double tube system, where an external field is applied in a certain direction in order to have a stronger inter-tube interaction than intra-tube interaction. The obtained (pseuso-)spin ferromagnetism is manifested by the spontaneous first order inter-tube correlation between fermions. The other system is by applying an external AC field, which can cause a strong coupling between different rotational states of molecules, leading to a ferro- electricity in a 3D enlongated harmonic trap. For bosonic case, we further show that such transition can be either second order or the first order, depending on internal nature of the molecules. We further show how these itinerant ferro-electricity can be manipulated by changing external trapping parameters.

2010/1/12(Tue) 13:00
speaker Shimpei Endo
title BEC-BCS crossover for Imbalanced system and its rich normal phases.
abstract A powerful experimental technique, Feshbach resonance, has provided us with an ability to study a close relation between BEC and BCS states, and also their strong coupling regime unexplored before. Recently, with a potential to control the number of particles of each spin states, we can also study the imbalanced Fermi system, where the number of spin up Fermions is different from that of spin down ones. In such system, various exotic superfluid phases have been proposed, such as FFLO states, mixture of 2 p-wave superfluids, or mixture of BEC and p-wave superfluids.

Today, I would like to concentrate on their normal phases, rather than superfluid phases and characterize their nature in each simple limits. The propertis of normal phases seem to be quite interesting and also theoretically challenging even in these limits, suggesting a novel crossover phenomenon of polaron physics. I will fistly explain some basics about BEC-BCS crossover and then characterize some simple limits of normal phases. The most challenging final goal, smoothly connecting all those normal states, will be left for the next seminar.

2010/1/19(Tue) 13:00
speaker Nguyen Thanh Phuc
title Phase Transitions in Spinor BECs
abstract The continuous phase transitions can be qualitatively well described by Ginzburg-Landau theory. In this seminar I will examine possible phase transitions in 3D Spinor Bose Systems by using this theory.
For 2-dimensional systems, the effect of fluctuations is so large that it can destroy the long range order of the system. In addition, there is a characteristic phase transition, called Berezinskii-Kosterlitz-Thouless (BKT) transition, for 2D systems. This phase transition is mediated by the unbinding of vortex pairs, a kind of topological defect existing in 2D systems. I will also introduce in this seminar some ideas of BKT transition in 2D Spinor Bose systems.

2010/1/26(Tue) 13:00
speaker Hideki Yamaguchi
title On the information processing ability of Escherichia coli
abstract It is known that Escherichia coli, one of unicellular organisms, has several interesting characteristics, two of which will be reviewed in this seminar: "fuzzy" logical operation and certain ability to "interpret" input information.
I will start with short introductory biology, and prepare for supplementary materials for technical terms. I hope that these will constitute the basis for theoretical considerations and future discussions.

2010/2/9(Tue) 13:00
speaker Sousuke Ito
title Derivation of the fluctuation theorem
abstract The fluctuation theorem is the relation which is valid for system driven arbitrarily far-from-equilibrium. This was originally derived for systems evolving under deterministic non-Hamiltonian equations of motion. And the fluctuation theorem is also derived for stochastic dynamics. In this seminar, I will mainly talk about these derivations and interpret the differences in derivations.
speaker Kyogo Kawaguchi
title Mutual Information and Entropy Production
abstract Landauer's principle, saying there is an unavoidable physical entropy production in the information erasure process, has long been assumed as the fundamental rule on how "information is physical". However, Sagawa-Ueda(2009) showed that the entropy production is related to the mutual information between the system and the measuring instrument. In this talk, I will explain how their interpretations on the "information thermodynamics" problem differ in a simple manner, considering the Szilard Engine and a deterministic two-system model.
speaker Tomoya Hayata
title Renormalization and Triviality
abstract It is well known that a simple perturbative calculation in quantum field theory (Q.F.T) often diverges and renormalization is needed. In this seminar, I will perform renormalization and examine its fundamental problem called triviality, using a familiar λφ4 interaction. Triviality is a crucial problem of Q.F.T that we can't make a consistent theory in all scale, unless the theory is non-interacting (and thus meaningless) i.e. coupling constant λ is 0. I will talk about the interpretation of this problem.

2010/3/2(Tue) 13:00
speaker Masahiro Takahashi
title Low-Energy Excitation Spectra of Spinor BECs and Ground State Properties of Dipole-Dipole Interaction Dominated BECs
abstract We have investigated (A) stability of spinor Bose-Einstein condensates (BECs) and (B) ground state properties of dipole-dipole interaction (DDI) dominated BECs. These are the comprehensive study of two limits of spinor BECs, namely, small hyperfine spin F and large F throughout this work, we can see whole spinor system approaching from two opposite limits.
For the study (A), we have focused on the state called coreless vortex state or Mermin-Ho vortex state, which is continuously transformed from a spin-polarized state. The coreless vortex state can be the ground state in rotating spinor BECs. On the other hand, the vortex states are experimentally realized in non-ferromagnetic interaction regions for F=1 and F=2 spinor BECs. Here we discuss the instability called ``dynamical instability'' to justify their stabilities of created coreless vortex states in experiments [1, 2]. Moreover, outcome is applicable to the further discussion on the magnetic ground state property of the 87Rb (F=2), which was used in the above experiment. Another goal for this study is to propose spectroscopy to decide the magnetic phase.was giving methodology to decide their phases [3].
For the study (B), we gave investigated ground state configuration of DDI dominated BECs by introducing classical spin model Hamiltonian. For the large F system, there are difficulties calculating ground state properties with full-quantum Hamiltonian since one has to handle 2F+1 equations to minimize the energy. By assuming classical spins, the spin degrees of freedom is reduced to the angles of the spin. Our proposed Hamiltonian is found to be valid for large F systems, while there is similarity to the results derived in small F system [4, 5].
We will present the details of the above studies and visions of future studies.

[1] M. Takahashi, V. Pietila, M. Mottonen, T. Mizushima and K. Machida, Phys. Rev. A 79 023618 (2009) [Virt. J. Nano. Sci. Tech. 19 9 (2009)].
[2] M. Takahashi, V. Pietila, M. Mottonen, T. Mizushima and K. Machida, Journal of Physics: Conference Series 150 032103 (2009).
[3] M. Takahashi, T. Mizushima and K. Machida, J. Low Temp. Phys. 158 58 (2010).
[4] M. Takahashi, S. Ghosh, T. Mizushima and K. Machida, Phys. Rev. Lett. 98 260403 (2007).
[5] M. Takahashi, S. Ghosh, T. Mizushima and K. Machida, Eur. Phys. J. B 68 391 (2009).

Schedule of summer semester (start from 13:00 @ #933 or #431)
4/28 (Tue) #933 : T. Sagawa
    "Quantum Measuring Processes of Continuous observables"
    Masanao Ozawa, J. Math. Phys. 25, 79 (1984).

5/19 (Tue) #933 : Y. Watanabe
    "Statistical Problems in Quantum Physics"
    A. S. Holevo, Proceedings of the Second Japan-USSR Symposium on Probability Theory
    (Lecture Notes in Mathematics), Berlin, Springer-Verlag, 330 104 (1973).
6/15 (Mon) #512 : H. Tajima
    "Quantum Tunnelling in a Dissipative System"
    A. O. CALDEIRA and A. J. LEGGETT, Annals of Physics 149, 374 (1983)

2009/6/16(Tue) #933 13:30-
speaker Takuya Kitagawa (Harvard University)
title Probe of strongly correlated state through noise correlation, from non-equilibrium physics to d-wave pair detection in ultracold atoms
abstract Recently, ultracold atoms are successfully used to experimentally realize systems with high controllability. Experimentalists can now prepare different dimensionality of the system, strength of interactions, or statistics of particles (Bosons or/and Fermions with varying number of internal degrees of freedom). This ability to engineer the system lead the the realization of, for example, Luttinger Liquid (Phys. Rev. Lett. 100, 140401 (2008)) and Mott insulating state with Hubbard model (Science 322,1520(2008)). These experiments not only shed light on the conventional condensed matter physics, but also it offers an unique opportunity to explore the physics (especially strongly correlated state) that was not accessible before.
In this talk, we propose the methods to study strongly correlated state through noise correlations ,taking advantage of the tools available in ultracold atoms. We believe these probes are accessible with current technology. In the first half of the talk, we present the study for the dynamical evolution of Luttinger Liquid through noise. We demonstrate noise characterizes the strong quantum fluctuations in 1D. In the second half of the talk, we present the scheme to detect the nature of paring in molecules. This scheme allows the detection of d-wave pairing in BCS-like state as well as the confirmation of p-wave molecules recently realized in JILA (Phys. Rev. Lett. 98, 200403 (2007)).

7/7 (Tue) #933 : Y. Kuramochi
    "Quasi-Particles and Gauge Invariance in the Theory of Superconductivity"
    Yoichiro Nambu, Phys. Rev. 117, 648 (1960).

7/8 (Wed) #431 : N. T. Phuc
    "Bose Condensation in an Attractive Fermion Gas:
        From Weak to Strong Coupling Superconductivity "

    P. Nozieres and S. Schmitt-Rink, Journal of Low Temperature Physics. 59, 195 (1985).

7/14 (Tue) #933 : H. Yamaguchi
    "Deterministic Nonperiodic Flow" (mirror)
    Edward N. Lorenz, Journal of the Atmospheric Sciences 20, 130 (1963)

7/21 (Tue) #431 : S. Kobayashi
    "Topological invariant and the quantization of the Hall conductance"
    Mahito Kohmoto, Annals of Physics. 160, 343 (1985).

7/22 (Wed) #233 : S. Endo
    "A Theoretical Description of the New Phases of Liquid 3He"
    Anthony J. Leggett, Rev. Mod. Phys. 47, 331 (1975)