RQC Seminar

260th RQC Seminar

• Speaker

  Dr. Alberto Mercurio
  ( The Swiss Federal Institute of Technology in Lausanne (EPFL) )

• Date

  14:00-15:00, (2:00 p.m.-3:00 p.m.) Monday, April 20, 2026

• Venue

  Hybrid( Zoom,
  345-347 Seminar Room, 3F, Main Research Building, Wako Campus / 和光地区 研究本館3階 セミナー室 (345-347) (C01))

• Title

  Floquet Dissipative Phase Transitions

• Inquiries

  norilab_rqc_assist[at]ml.riken.jp

Abstract
Dissipative phase transitions (DPTs) have emerged as a hallmark of critical phenomena in open quantum systems, typically characterized by the closing of the spectral gap of a timeindependent Liouvillian. However, this static definition becomes inapplicable in periodically driven systems, where the generator of dynamics is inherently time-dependent. In this talk, I will present a general framework to characterize DPTs in such systems by analyzing the spectrum of the Floquet propagator, defining the transition through the closure of the Floquet spectral gap.
We first apply this framework to the driven Kerr resonator, demonstrating that the standard Rotating Wave Approximation (RWA) fails to capture the true critical boundaries. We show that counter-rotating terms in the drive lead to significant shifts in the critical point and spectral properties relative to standard predictions.
Crucially, we extend this analysis to the driven quantum Rabi model, contrasting it with the Jaynes-Cummings model. While the time-dependence in the Jaynes-Cummings model can be removed via a unitary transformation to a rotating frame, the counter-rotating terms in the quantum Rabi model enforce an intrinsic time-periodicity that cannot be gauged away. We show that this results in distinct critical features in the steady state.
Consequently, our Floquet spectral analysis is essential to capture the influence of counter-rotating terms on the phase transition.