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Output field squeezing in a weakly-driven dissipative quantum Rabi model
摘要： We present a generalized method to address the squeezing spectrum of the output field for a weakly-driven, dissipative quantum Rabi model and calculate it for a range of coupling strengths covering strong, ultra-strong and deep-strong coupling regimes. The need for a generalization arises because of the periodic time dependence of the correlation functions due to counterrotating terms in the quantum Rabi model. We here adopt time-averaging over such correlation functions to obtain the squeezing spectrum, which may also be relevant to experimental situations. We compare the calculated squeezing spectra with those of the driven dissipative Jaynes-Cummings model to illustrate the departure from the latter as the interaction strength increases. Our calculation shows that the overall squeezing increases with the interaction strength after optimization over the system-bath coupling strength and the driving field strength.
关键词： Quantum Rabi model,Jaynes-Cummings model,Spectrum of squeezing
更新于2025-09-23 15:21:21
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Ultrastrong-coupling regime of nondipolar light-matter interactions
摘要： We present a circuit-QED scheme which makes it possible to reach the ultrastrong-coupling regime of a nondipolar interaction between a single qubit and a quantum resonator. We show that the system Hamiltonian is well approximated by a two-photon quantum Rabi model and propose a simple scattering experiment to probe its fundamental properties. In particular, we identify a driving scheme that reveals the change in selection rules characterizing the breakdown of the rotating-wave approximation and the transition from strong to ultrastrong two-photon interactions. Finally, we show that a frequency crowding in a narrow spectral region is observable in the output fluorescence spectrum as the coupling strength approaches the collapse point, paving the way to the direct observation of the onset of the spectral collapse in a solid-state device.
关键词： nondipolar light-matter interactions,spectral collapse,two-photon quantum Rabi model,ultrastrong-coupling regime,circuit-QED
更新于2025-09-23 15:21:01
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Gauge ambiguities imply Jaynes-Cummings physics remains valid in ultrastrong coupling QED
摘要： Ultrastrong-coupling between two-level systems and radiation is important for both fundamental and applied quantum electrodynamics (QED). Such regimes are identified by the breakdown of the rotating-wave approximation, which applied to the quantum Rabi model (QRM) yields the apparently less fundamental Jaynes-Cummings model (JCM). We show that when truncating the material system to two levels, each gauge gives a different description whose predictions vary significantly for ultrastrong-coupling. QRMs are obtained through specific gauge choices, but so too is a JCM without needing the rotating-wave approximation. Analysing a circuit QED setup, we find that this JCM provides more accurate predictions than the QRM for the ground state, and often for the first excited state as well. Thus, Jaynes-Cummings physics is not restricted to light-matter coupling below the ultrastrong limit. Among the many implications is that the system's ground state is not necessarily highly entangled, which is usually considered a hallmark of ultrastrong-coupling.
关键词： quantum Rabi model,circuit QED,gauge invariance,Jaynes-Cummings model,ultrastrong coupling,quantum electrodynamics
更新于2025-09-19 17:15:36
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Photodetection probability in quantum systems with arbitrarily strong light-matter interaction
摘要： Cavity-QED systems have recently reached a regime where the light-matter interaction strength amounts to a non-negligible fraction of the resonance frequencies of the bare subsystems. In this regime, it is known that the usual normal-order correlation functions for the cavity-photon operators fail to describe both the rate and the statistics of emitted photons. Following Glauber’s original approach, we derive a simple and general quantum theory of photodetection, valid for arbitrary light-matter interaction strengths. Our derivation uses Fermi’s golden rule, together with an expansion of system operators in the eigenbasis of the interacting light-matter system, to arrive at the correct photodetection probabilities. We consider both narrow- and wide-band photodetectors. Our description is also valid for point-like detectors placed inside the optical cavity. As an application, we propose a gedanken experiment confirming the virtual nature of the bare excitations that enrich the ground state of the quantum Rabi model.
关键词： Cavity-QED,light-matter interaction,ultrastrong coupling,quantum Rabi model,photodetection
更新于2025-09-04 15:30:14