今期の予定
日時：2026年4月8日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：Sidharth Rammohan（量子多体）
題目：Cluster mean-field analysis on quantum dynamics in a planar array
of hardcore Bose-Hubbard chains with interchain interactions
概要：Dipolar bosons in optical lattices offer a versatile platform for quantum simulation, as their long-range and anisotropic interactions give rise to strongly correlated many-body phenomena. These properties have attracted significant experimental and theoretical interest in the study of emergent quantum phases [1,2]. In one-dimensional (1D) settings, such systems exhibit a collective behavior that can be effectively described by Luttinger liquid (LL) theory. Extending this framework to arrays of weakly coupled one-dimensional chains naturally raises the question of how interchain interactions lead to new quantum phases. In this context, the sliding Luttinger liquid (SLL) phase has been proposed as a stable state of weakly coupled 1D chains, where each chain retains its Luttinger-liquid character while interchain interactions enable phase sliding without establishing long-range order [3]. Realizing the SLL phase experimentally is challenging, as it requires strong interchain interactions while keeping the fluctuations minimal. Dipolar ultracold atomic systems, with their tunable long-range interactions, offer a promising platform for observing such a phase, and have consequently motivated theoretical studies exploring planar arrays of dipolar bosons as a route to realizing it [4]. However, existing theoretical studies have focused on equilibrium properties, and real-time dynamics of these systems remain relatively unexplored.
日時：2026年4月15日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：Jose Carlos Pelayo（量子多体）
題目：Multipolar structure in a Rydberg chain with a Four-level Förster resonance
概要：We investigate a chain of four-level Rydberg atoms exhibiting both two-level and four-level Förster resonances, the latter enabled by a local light field [1]. We analyze the system using a mean-field approach based on an effective spin-1/2 representation near the degenerate levels, and compare it with a full spin-3/2 mean-field treatment. Within the effective spin-1/2 description, we identify XY ferromagnetic, XY antiferromagnetic phases [2] and Ising Néel. Mapping these states back to the full spin-3/2 Hilbert space reveals an associated multipolar structure, that is pronounced near the four-level Förster resonance. These results are compared against matrix product state (MPS) calculations.
[1] Emperauger, Gabriel, et al. "Benchmarking direct and indirect dipolar spin-exchange interactions between two Rydberg atoms." Physical Review A 111 no. 6 (2025)
[2] Chen, Cheng, et al. "Continuous symmetry breaking in a two-dimensional Rydberg array." Nature 616 no. 7958 (2023)
日時：2026年4月22日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：古内 理人（量子多体）
題目：Domain formation dynamics in Rydberg-atom arrays described by a mixed-field Ising model on a square lattice
概要：Rydberg-atom systems have recently attracted considerable attention as highly controllable platforms for quantum simulation and quantum computation. Because both the spatial arrangement of atoms and the interactions induced by Rydberg excitation can be controlled, these systems provide a suitable platform for investigating nonequilibrium dynamics. In particular, a Rydberg-atom system can be described by mapping the ground and excited states of each atom onto pseudospin states can be described by a S=1/2 mixed-field Ising model [1]. Recent experiments [2] using such a Rydberg-atom system have addressed quantum dynamics after a quantum quench of the transverse and longitudinal fields starting from a fully polarized (all spin-down) state. It has been found that when a resonance condition called facilitation condition is satisfied, the cluster size of up-spin domains significantly grows in time [2].
In this study, aiming to understand mechanisms of the observed domain-formation dynamics, we theoretically investigate the quench dynamics in a relatively small system, where we can diagonalize the full Hamiltonian of the system and calculate the time evolution of an initial state using the resulting eigenvalues and eigenvectors. We discuss characteristic features of the time evolution by comparing them with the predictions of a pseudo-analytical perturbation theory that treats the transverse field as a perturbation.
[1]A. Browaeys and T. Lahaye, Nat. Phys. 16, 132 (2020).
[2] Philip Osterholz et al. arXiv preprint arXiv:2512.04656v2 (2026).
日時：2026年5月7日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：奥 奏太（物性理論）
題目：Numerical Analysis of Two-Dark-Soliton Collisions in a Driven-Dissipative Exciton-Polariton Condensate and Improvement of an Effective Equation of Motion
概要：Exciton-polariton condensates are nonequilibrium condensates formed through strong coupling between excitons and cavity photons in semiconductor microcavities [1]. Owing to their small effective mass, macroscopic coherence, and nonlinear interactions, they provide a useful platform for studying nonequilibrium quantum-fluid dynamics. Dark solitons are an important class of nonlinear excitations in such condensates. In contrast to conservative condensates, however, polariton condensates have finite lifetimes and are maintained by a balance between external pumping and dissipation. This driven-dissipative nature modifies the lifetime and dynamics of dark solitons [2]. In this study, we numerically analyze collisions between two dark solitons in a one-dimensional driven-dissipative exciton-polariton condensate.
We solve the coupled partial differential equation (PDE) system consisting of a driven-dissipative Gross-Pitaevskii equation and a reservoir-density equation under periodic boundary conditions. From the numerical density profiles, we track local density minima and extract the inter-soliton separation η(t). We then compare η_PDE(t), obtained from the PDE simulations, with η_ODE(t), obtained from an effective equation of motion formulated as an ordinary differential equation (ODE) for the relative coordinate [3]. By sweeping the reservoir decay rate γ_R and the stimulated scattering coefficient R̄, we evaluate the root-mean-square error (RMSE) during the post-collision repulsive dynamics and visualize the parameter dependence of the agreement between the PDE and ODE results using heat maps. We also show that an improved treatment of the reservoir contribution, incorporating local density dependence, systematically reduces the RMSE in parameter regions where the inter-soliton separation can be reliably extracted.
参考文献:[1] S. Ghosh, R. Su, J. Zhao, A. Fieramosca, J. Wu, T. Li, Q. Zhang, F. Li, Z. Chen, T. C. H. Liew, D. Sanvitto, and Q. Xiong, Photonics Insights 1, R04 (2022).
[2] L. A. Smirnov, D. A. Smirnova, E. A. Ostrovskaya, and Y. S. Kivshar, Phys. Rev. B 89, 235310 (2014).
[3] Y. Zhang, C. Jia, and Z. Liang, arXiv preprint arXiv:2112.03559v1 (2021).
日時：2026年5月13日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：Edwin Chaparro (JILA, University of Colorado)
題目：Bidirectional Teleportation Using Scrambling Dynamics: A Practical Protocol
概要：We show that quantum information scrambling can enable a generic SWAP gate between collective degrees of freedom in systems without universal local control. Our protocol combines the Hayden–Preskill recovery scheme, associated with the black hole information paradox, with quantum teleportation and runs them in parallel and in opposite directions, enabling bidirectional exchange of quantum states through global interactions alone. This approach cleanly distinguishes the roles of information spreading, entanglement, and chaos for enabling both coherent state transfer and recovery. We propose an experimental realization using the Dicke model, which can be realized in cavity-QED and trapped-ion platforms, highlighting the utility of holography in designing practical quantum gates.
日時：2026年5月20日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：川崎 大生（量子多体）
題目：TBA
概要：TBA
日時：2026年6月3日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：庄野 滉平（場の量子論・素粒子論研究室）
題目：TBA
概要：TBA
日時：2026年6月10日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：Mengxuan Xia（場の量子論・素粒子論研究室）
題目：TBA
概要：TBA
日時：2026年6月17日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：吉田 啓（物性理論）
題目：TBA
概要：TBA
日時：2026年6月24日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：小林 麟太郎（量子多体）
題目：TBA
概要：TBA
日時：2026年7月1日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：田中 愛梨（物性理論）
題目：TBA
概要：TBA
日時：2026年7月8日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：百合 巧（大阪大学）
題目：TBA
概要：TBA
日時：2026年7月15日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：吉本 康晟（量子多体）
題目：TBA
概要：TBA
日時：2026年7月22日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者：渡部 元輝（分子科学研究所）
題目：TBA
概要：TBA
日時：2026年7月29日15:00-
教室：31号館4階数物会議室+Zoom配信
発表者1：TBA
題目：TBA
概要：TBA