[講演者] : Zongping Gong 氏

[日時] 5月28日 16:30-

[場所] 物理学科会議室

[タイトル]：Discrete Time-Crystalline Order in Cavity and Circuit QED Systems

[アブストラクト] :

Discrete time crystals (DTCs) are a recently proposed [1-3] and experimentally observed [4,5] nonequilibrium dynamical phase of Floquet systems, where the stroboscopic evolution of a local observable repeats itself at an integer multiple of the driving period. Previous works focused mainly on closed quantum systems because the coupling to an environment is believed to typically kill the discrete time-crystalline (DTC) order [6]. In this seminar, we will see that the DTC order does exist in specific open quantum system [7], as conjectured in Ref. [8]. We exemplify such a dissipative DTC by the modulated open Dicke model, which can be implemented by cavity and circuit QED systems [9,10]. In the thermodynamic limit, we employ semiclassical approaches and find rich dynamical phases on top of the DTC order. The rich phase structure can systematically be understood from bifurcation theory. In a deep quantum regime with few qubits, we find clear signatures of a transient DTC behavior, which is absent in the closed counterpart. This behavior can simply be understood from the spectrum of the Floquet superoperator. We also establish a phenomenology of dissipative DTCs by generalizing the Landau theory of phase transitions to Floquet open systems. In particular, we demonstrate the exponential scaling for the lifetime of the DTC mode with respect to the system size.

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