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)
夏学期 / Summer semester (April-July 2026)
<Regular seminars (review of seminal papers)>木曜日15時から理学部１号館233号室で行います(普段と場所or時間の異なる場合は赤字で示します)。
Each seminar starts from 15:00, Thursday @ #233, Faculty of Science Bldg. 1 (unless otherwise indicated).
<Schedule>
Apr. 9 H. Li
"Spectral Gap and
Exponential Decay of Correlations"
Matthew B. Hastings and Tohru Koma, Commun. Math. Phys. 265, 781-804 (2006).
Apr. 16 Iyama
"Solution of 'Solvable
model of a spin glass'"
D. J. Thouless, P. W. Anderson, and R. G. Palmer, Philos. Mag. 35(3), 593-601 (1977).
Apr. 23 Yamada
"Emergent Hydronamics
in Integrable Quantum Systems Out of Equilibrium"
O. A. Castro-Alvaredo, B. Doyon, and T. Yoshimura, Phys. Rev. X 6, 041065 (2016).
Apr. 30 Hokkyo (online)
"Symmetry breaking in Heisenberg
antiferromagnets"
T. Koma and H. Tasaki, Commun. Math. Phys. 158, 191 (1993).
May. 7 (No seminar)
May. 14 (No seminar)
May. 21 (No seminar)
May. 28 Ishii (online)
"Minimum mean-squared
error of estimates in quantum statistics"
C.W. Helstrom, Physics Letters A
25, 101 (1967).
"Multiple-parameter quantum estimation and
measurement of nonselfadjoint observables"
H.P. Yuen
and M. Lax, IEEE Transactions on Information Theory 19, 740 (1973).
Jun. 4 Sugiura (online)
"Fault-tolerant quantum computation by anyons"
Alexei Yu. Kitaev, Annals of Physics 303, 2-30 (2003).
Jun. 11 (No seminar)
Jun. 18 Yutani
"On the generators of quantum dynamical semigroups"
G. Lindblad, Commun. Math. Phys. 48, 119 (1976).
Jun. 25 (No seminar)
Jul. 2 Oyaizu
"Topological quantum memory"
E. Dennis, A. Kitaev, A. Landahl, and J. Preskill, J. Math. Phys. 43, 4452 (2002).
Jul. 9 Tanii
"Neural networks and physical systems with emergent collective computational abilities"
J. J. Hopfield, Proc. Natl. Acad. Sci. 79, 2554 (1982).
Jul. 16 H. Nakagawa
"Diatomic molecules and Cooper pairs"
A. J. Leggett, Modern Trends Theor. Cond. Mat. 115, 13 (1980).
冬学期 / Winter semester (October 2026-January 2027)
木曜日16時から理学部１号館233号室で行います(普段と場所or時間の異なる場合は赤字で示します)。Each seminar starts from 16:00, Thursday @ #233, Faculty of Science Bldg. 1 (unless otherwise indicated).
<Schedule>
10/8 Sugiura / Yukawa (from 15:00)
10/15 Morita / Saboo (from 15:00)
10/22 Hokkyo (from 15:00)
10/29 Iyama
11/5 (No seminar)
11/12 Yamada
11/19 Nakanishi (@414)
11/26 Kai Li
12/3 Gong (@913)
12/10 (No seminar)
12/17 (No seminar)
12/24 Yutani
12/31 (No seminar)
1/7 Nakagawa
1/14 Ishii (online)
1/21 Oyaizu
1/28 B4 / B4
| speaker | Shuma Sugiura |
| title | Theory for Feedback Cooling of a Levitated Nanoparticle in Experiment |
| abstract | Optically levitated nanoparticles provide a promising platform for investigating macroscopic quantum phenomena, for which ground-state cooling is an important prerequisite. In this seminar, I will present a theoretical analysis of feedback cooling of a levitated nanoparticle, with an emphasis on comparison with experimental results. Starting from a quantum measurement model, we formulate the dynamics of a continuously monitored nanoparticle under measurement-based feedback control. By incorporating the frequency-dependent transfer function of the feedback system, we calculate the phonon occupation number and the power spectral density (PSD) of the measurement signal. Our theoretical model quantitatively reproduces the experimentally observed optimal feedback gain, although discrepancies remain in the predicted phonon occupation number. Furthermore, the model qualitatively reproduces a characteristic shoulder in the in-loop PSD that cannot be explained by an ideal low-pass-filter feedback model. We show that this shoulder arises from the frequency dependence of the phase response of the feedback system. |
| speaker | Emi Yukawa |
| title | Information Retrieval from Noisy Squeezed Spin States via Bayesian Optimization |
| abstract | Quantum entanglement is often masked in noisy environments. When frequencies of spins in a spin ensemble vary due to inhomogeneous broadening, the squeezing parameter degrades and it becomes difficult for the sensitivity of Ramsey interferometry to go beyond the standard quantum limit. In this presentation, we show that the masked information about a magnetic field encoded in a squeezed spin state can be retrieved by measuring an appropriate linear combination of a magnetic dipole and quadrupoles by means of the Bayesian optimization method. |
| speaker | Yusuke Morita |
| title | Exciton Bose-Einstein Condensation: Discovery and Future Challenges |
| abstract | Excitons are bosonic quasiparticles composed of an electron and a hole. Because they have a finite lifetime, exciton Bose–Einstein condensation (BEC) occurs in a nonequilibrium open system, in contrast to conventional equilibrium BECs. Moreover, bosons composed of particle–antiparticle pairs are expected to exhibit condensation properties distinct from those of bosons composed only of particles. Exciton BEC therefore provides a unique platform for addressing fundamental questions in quantum physics. Recently, exciton BEC was experimentally observed for the first time, opening new possibilities for studying quantum many-body phenomena in such systems. In this presentation, I will introduce the basic properties of excitons and the concept of exciton condensation, followed by an overview of the experiments that led to the observation of BEC. I will also discuss future perspectives, including physical phenomena and properties that may be explored through further experimental investigations of exciton condensates. |
| speaker | Arpana Saboo |
| title | Driven-Dissipative Theory of Paraexciton Bose-Einstein Condensation in Cu2O |
| abstract |
Paraexcitons in Cu2O have long been a leading candidate for exciton Bose–Einstein condensation, and a condensate has recently been observed, yet with a condensate fraction far below that of an equilibrium atomic BEC. In this seminar, I will present a microscopic theory of paraexciton condensation, with an emphasis on the fact that the condensate is a continuously driven, continuously decaying system rather than an equilibrium Bose gas. Starting from the electron–hole and exciton–phonon Hamiltonian, we formulate the kinetics of a continuously pumped, lossy exciton gas under generation, ortho-to-para conversion, acoustic-phonon cooling, Bose-stimulated gain, recombination, and Auger loss. By treating each of these as a microscopic rate, we derive a driven–dissipative Gross–Pitaevskii equation and reduce it, in the stationary state, to a closed set of equations for the condensate and non-condensate densities. Solving these exactly, we obtain the condensate fraction and the condensation threshold. We show that the full result collapses onto a universal phase diagram governed by only two dimensionless groups; the Auger-to-gain ratio and the scaled pump, on which the condensate fraction is intrinsically bounded below unity by the two-body Auger loss. Within this picture, a small condensate fraction appears not as a shortfall from equilibrium but as the natural steady state of a driven, Auger-drained condensate. |
| speaker | Akihiro Hokkyo |
| title | TBA |
| abstract | TBA |
| speaker | Naoki Iyama |
| title | TBA |
| abstract | TBA |
| speaker | Shozo Yamada |
| title | TBA |
| abstract | TBA |
| speaker | Ken Nakanishi |
| title | TBA |
| abstract | TBA |
| speaker | Kai Li |
| title | TBA |
| abstract | TBA |
| speaker | Ming Gong |
| title | TBA |
| abstract | TBA |
| speaker | Ryota Yutani |
| title | TBA |
| abstract | TBA |
| speaker | Masaya Nakagawa |
| title | TBA |
| abstract | TBA |
| speaker | Takanao Ishii |
| title | TBA |
| abstract | TBA |
| speaker | Atsushi Oyaizu |
| title | TBA |
| abstract | TBA |
| speaker | B4 |
| title | TBA |
| abstract | TBA |
| speaker | B4 |
| title | TBA |
| abstract | TBA |