197th RQC Seminar

• 講演者

  Mr. Gabriele Orlando
  ( University of Messina, Italy )

• 日程

  2025年5月19日（月） 16:00-17:00 (4:00 p.m. - 5:00 p.m.)

• 開催場所

  ハイブリッド（ZOOM・ Wako Main Research 3F 345-347 Seminar Room / 研究本館3階 セミナー室 (345-347) (C01))

• 講演タイトル

  Superradiant Quantum Phase Transition in Open Systems : The System-Baths Interaction at the Critical Point

• お問合せ

  norilab_rqc_assist[at]ml.riken.jp

講演概要
The occurrence of a second-order quantum phase transition in the Dicke model is a well-established feature. On the contrary, a comprehensive understanding of the corresponding open system, particularly in the proximity of the critical point, remains elusive. When approaching the critical point, the system inevitably enters first the system-bath ultrastrong coupling regime and finally the deep strong coupling regime, causing the failure of usual approximations adopted to describe open quantum systems. We study the interaction of the Dicke model with bosonic bath fields in the absence of additional approximations, which usually relies on the weakness of the system-bath coupling [1]. We find that the critical point is not affected by interactions with environments displaying metastable minima. Moreover, such interactions cannot affect the system ground-state condensates in the superradiant phase, whereas the bath fields are infected by the system and acquire macroscopic occupations. We obtain analytical formulas for the reflection spectra, both in the normal and superradiant phases, in the presence of ohmic baths and not. %clarifying the evolution of the line broadening in presence of the softening of the polariton frequency and its evolution in the abnormal phase.The obtained reflection spectra display lineshapes which become increasingly asymmetric, both in the normal and superradiant phases, when approaching the critical point.

[1] D. Lamberto, Superradiant Quantum Phase Transition in Open Systems: System-Bath Interaction at the Critical Point, arXiv:2411.16514 (2025)