UEDA GROUP

Department of Physics, The University of Tokyo

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2024年 / Academic Year 2024

研究室メンバーによるレギュラー・セミナー、 および、他研究室・機関からのゲスト・スピーカーのセミナーを開催しています。 レギュラー・セミナーは下記要領で行います。 Access map：理学部1号館 (Faculty of Science Bldg. 1) / 理学部4号館 (Faculty of Science Bldg. 4)

Each seminar starts

**<Schedule>**

Apr. 18 Hokkyo

"The Classical Limit of Quantum Spin Systems"

E. H. Lieb, Commun.Math. Phys. 31, 327-340 (1973).

Apr. 25 (No seminar)

May. 2 Shiraishi

"Theory of Thermal Transport Coefficients"

J. M. Luttinger, Phys. Rev. 135, A1505 (1964).

"A Quantum-statistical Theory of Transport Processes"

H. Mori, J. Phys. Soc. Jpn. 11 1029 (1956).

May. 9 Li

"Exact Analysis of an Interacting Bose Gas. I. The General Solution and the Ground State"

E. H. Lieb and W. Liniger, Phys. Rev. 130, 1605 (1963).

"Exact Analysis of an Interacting Bose Gas. II. The Excitation Spectrum"

E. H. Lieb, Phys. Rev. 130, 1616 (1963).

May. 16 (No seminar)

May. 23 (No seminar)

May. 30 Sakamoto(starting from 3pm)

"Quantum cryptography: Public key distribution and coin tossing"

C.H. Bennett, G. Brassard, Proceedings of IEEE International Conference on Computers Systems and Signal Processing, Bangalore India, 175 (1984).

Jun. 6 Sugiura

"The renormalization group and the ϵ expansion"

Kenneth G. Wilson and J. Kogut, Physics Reports 12, 2, 75-199 (1974).

Jun. 13 Ishii

"'Luttinger liquid theory' of one-dimensional quantum fluids. I. Properties of the Luttinger model and their extension to the general 1D interacting spinless Fermi gas"

F. D. M. Haldane, Journal of Physics C: Solid State Physics, 14(19), 2585 (1981).

Jun. 20 Ogawa (B4 student)

"The Uncertainty Relation Between Energy and Time in Non-relativistic Quantum Mechanics"

L. Mandelstam and Ig. Tamm, J. Phys. USSR 9, 249-254 (1945).

"The maximum speed of dynamical evolution"

Margolus Norman and Lev B. Levitin, Physica D: Nonlinear Phenomena 120.1-2 (1998): 188-195.

"New form of the time-energy uncertainty relation"

Eric A. Gislason, Nora H. Sabelli, and John W. Wood, Phys. Rev. A 31, 2078 (1985).

Jun. 27 (No seminar)

Jul. 4 Kandabashi (B4 student)

"Nonequilibrium Equality for Free Energy Differences"

C. Jarzynski, Phys. Rev. Lett. 78(14) 2690 (1997).

Jul. 11 Oyaizu (@233 → changed to 913)

"Classical Time Crystals"

Alfred Shapere and Frank Wilczek, Phys. Rev. Lett. 109, 160402 (2012).

"Quantum Time Crystals"

Frank Wilczek, Phys. Rev. Lett. 109, 160401 (2012).

Each seminar starts

10/3 (No seminar)

10/10 Kai Li/Hongchao Li (@414)

10/17 Sakamoto

10/24 Hokkyo

10/31 Ishii

11/7 (No seminar)

11/14 (No seminar)

11/21 (No seminar)

11/28 Nakagawa

12/5 (No seminar)

12/12 Shiraishi

12/19 Sugiura

12/26 (No seminar)

1/9 Oyaizu (@207)

1/16 Nohara / Yamada (@TBA)

2024/10/10 13:00- (@414)

speaker | Kai Li |

title | Probing non-Hermitian eigenenergies |

abstract |
While non-Hermitian Hamiltonians have been experimentally realized in cold atom systems, it remains an outstanding open question of how to experimentally measure their complex energy spectra in momentum space for a realistic system with boundaries. The existence of non-Hermitian skin effects may make the question even more difficult to address given the fact that energy spectra for a system with open boundaries are dramatically different from those in momentum space; the fact may even lead to the notion that momentum-space band structures are not experimentally accessible for a system with open boundaries. In this study [1], we generalize the widely used radio-frequency spectroscopy to measure both real and imaginary parts of complex energy spectra of a non-Hermitian quantum system for either bosonic or fermionic atoms. By weakly coupling the energy levels of a non-Hermitian system to auxiliary energy levels, we theoretically derive a formula showing that the decay of atoms on the auxiliary energy levels reflects the real and imaginary parts of energy spectra in momentum space. We prove that measurement outcomes are independent of boundary conditions in the thermodynamic limit, providing strong evidence that the energy spectrum in momentum space is experimentally measurable. We also discuss whether the spectrum under open boundary conditions can be measured when skin effects exist and how the interaction in the non-Hermitian system affects the measurement results.
[1] K. Li and Y. Xu, Phys. Rev. Lett. 129, 093001 (2022). |

2024/10/10 13:00- (@414)

speaker | Hongchao Li |

title | Dissipative Superfluidity in a Molecular Bose-Einstein Condensate |

abstract |
Quantum gases of dipolar molecules, which serve as a platform to realize clean and controllable long-range interacting systems, have received considerable attention in the fields of many-body physics and quantum simulation. However, heteronuclear molecules inevitably suffer the two-body loss due to chemical reactions, which is particularly serious for bosonic molecules. Recently, with the development of the microwave shielding
the first experimental realization of a BEC of heteronuclear molecules has been reported. Thus, it is of fundamental interest to understand whether or not superfluidity exists under two-body loss in such BECs, since dissipation may deteriorate the phase coherence of a superfluid. In this study [1], we develop superfluid transport theory for a dissipative BEC to show that a weak uniform two-body loss can induce phase rigidity, leading to superfluid transport of bosons even without repulsive interparticle interactions. We also show a generalized f-sum rule for a dissipative superfluid as a consequence of weak U(1) symmetry. Finally, we demonstrate that dissipation enhances the stability of a molecular BEC with dipolar interactions.
[1]: H. Li, X. Yu, M. Nakagawa, M. Ueda, arXiv: 2406.08868. |