No-go theorem for superradiant quantum phase transitions in cavity QED and counter-example in circuit QED

Nataf, Pierre; Ciuti, Cristiano

doi:10.1038/ncomms1069

Cited by 308 publications

(440 citation statements)

References 22 publications

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“…As for the circuit QED setup based on superconducting qubits, we note that, due to the absence of the TRK sum rule for the capacitive coupling, the A 2 term could be negligible in the strong-coupling regime without entering the rotating frame of reference [58] (although still controversial [59,61]). For the inductive coupling, while the Dicke phase transition has not yet been experimentally observed in superconducting circuits, the beyond-ultrastrong coupling has recently been realized for a single flux qubit [63].…”

Section: Circuit Qed Setup Based On Inductive Couplingmentioning

confidence: 99%

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Discrete Time-Crystalline Order in Cavity and Circuit QED Systems

2018

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Discrete time crystals are a recently proposed and experimentally observed out-of-equilibrium dynamical phase of Floquet systems, where the stroboscopic evolution of a local observable repeats itself at an integer multiple of the driving period. We address this issue in a driven-dissipative setup, focusing on the modulated open Dicke model, which can be implemented by cavity or circuit QED systems. In the thermodynamic limit, we employ semiclassical approaches and find rich dynamical phases on top of the discrete time-crystalline order. In a deep quantum regime with few qubits, we find clear signatures of a transient discrete time-crystalline behavior, which is absent in the isolated counterpart. We establish a phenomenology of dissipative discrete time crystals by generalizing the Landau theory of phase transitions to Floquet open systems.Introduction.-Phases and phase transitions of matter are key concepts for understanding complex many-body physics [1,2]. Recent experimental developments in various quantum simulators, such as ultracold atoms [3,4], trapped ions [5,6] and superconducting qubits [7,8], motivate us to seek for quantum many-body systems out of equilibrium [9][10][11], such as many-body localized phases [12][13][14][15][16][17] and Floquet topological phases [18][19][20][21][22][23][24][25].In recent years, much effort has been devoted to periodically driven (Floquet) quantum many-body systems that break the discrete time-translation symmetry (TTS) [26]. In contrast to the continuous TTS breaking [27][28][29] that has turned out to be impossible at thermal equilibrium [30,31], the discrete TTS breaking has been theoretically proposed [32][33][34][35][36] and experimentally demonstrated [37,38]. Phases with broken discrete TTS feature discrete time-crystalline (DTC) order characterized by periodic oscillations of physical observables with period nT , where T is the Floquet period and n = 2, 3, · · · . The DTC order is expected to be stabilized by many-body interactions against variations of driving parameters. Note that the system is assumed to be in a localized phase [33,34,36,37] or to have long-range interactions [38][39][40]. Otherwise, the DTC order only exists in a prethermalized regime [41,42] since the system will eventually be heated to a featureless infinite-temperature state due to persistent driving [43][44][45].While remarkable progresses are being made concerning the DTC phase, most studies focus on isolated systems. Indeed, as has been experimentally observed [37,38] and theoretically investigated [46], the DTC order in an open system is usually destroyed by decoherence. On the other hand, it is known that dissipation and decoherence can also serve as resources for quantum tasks such as quantum computation [47] and metrology [48]. From this perspective, it is natural to ask whether the DTC order exists and can even be stabilized in open systems [49]. Such a possibility has actually been pointed out in Ref. [41], but neither a detailed theoretical model nor a concrete experimental imp...

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Section: Circuit Qed Setup Based On Inductive Couplingmentioning

confidence: 99%

“…This model is relevant to cavity QED systems based on cold atoms [53][54][55][56] and circuit QED systems based on superconducting qubits [57][58][59][60][61][62][63]. As schematically illustrated in Fig.…”

Section: Fig 1: (Color Online)mentioning

confidence: 99%

Discrete Time-Crystalline Order in Cavity and Circuit QED Systems

2018

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“…The Dicke model is a quantum-optical model that describes the interaction of a radiation field with N two-level atoms [42]. This model has recently renewed interest [43][44][45][46], partly because a tunable matter-radiation interaction is a keynote ingredient for the study of quantum critical effects [15,47,48] and partly because the model phase transition has been observed experimentally [49]. The interacting boson model (IBM) was introduced by Arima and Iachello to describe the structure of low energy states of even-even medium and heavy nuclei [50].…”

Section: Introductionmentioning

confidence: 99%

Identifying the order of a quantum phase transition by means of Wehrl entropy in phase space

et al. 2015

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“…In particular, in the field of circuit QED, one of the promising candidates for reaching ultrastrong coupling, even a similar debate seems to have arisen concerning the feasibility of the superradiant phase transition [23][24][25][26] as in the QED of atoms. It is an interesting comparison that in atomic QED, as our approach demonstrates, a very precise microscopic modeling of the atoms and their interaction with the field seems to be necessary for judging the feasibility and the nature of the superradiant phase transition.…”

Section: Discussionmentioning

confidence: 99%

Depolarization shift of the superradiant phase transition

2016

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We investigate the possibility of a Dicke-type superradiant phase transition of an atomic gas with an extended model which takes into account the short-range depolarizing interactions between atoms approaching each other as close as the atomic size scale, which interaction appears in a regularized electric-dipole picture of the QED of atoms. By using a mean field model, we find that a critical density does indeed exist, though the atom-atom contact interaction shifts it to a higher value than it can be obtained from the bare Dicke-model. We argue that the system, at the critical density, transitions to the condensed rather than the "superradiant" phase.

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No-go theorem for superradiant quantum phase transitions in cavity QED and counter-example in circuit QED

Cited by 308 publications

References 22 publications

Discrete Time-Crystalline Order in Cavity and Circuit QED Systems

Discrete Time-Crystalline Order in Cavity and Circuit QED Systems

Identifying the order of a quantum phase transition by means of Wehrl entropy in phase space

Depolarization shift of the superradiant phase transition

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