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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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Universal Spectral Features of Ultrastrongly Coupled Systems
摘要： We identify universal properties of the low-energy subspace of a wide class of quantum optical models in the ultrastrong coupling limit, where the coupling strength dominates over all other energy scales in the system. We show that the symmetry of the light-matter interaction is at the origin of a twofold degeneracy in the spectrum. We prove analytically this result for bounded Hamiltonians and extend it to a class of models with unbounded operators. As a consequence, we show that the emergence of superradiant phases previously investigated in the context of critical phenomena, is a general property of the ultrastrong coupling limit. The set of models we consider encompasses different scenarios of possible interplay between critical behavior and superradiance.
关键词： superradiant phases,ultrastrong coupling,critical phenomena,quantum optical models
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Inhomogeneous Broadening of a Polaritonic Mode in the Ultrastrong Coupling Regime
摘要： Ultrastrong coupling (USC) regime has been an intriguing research topic in cavity quantum electrodynamics (QED) experiments due to its capability to modify the ground and the excited states of a coupled system[1-3]. We investigate the USC of Landau level (LL) transitions in a two dimensional electron gas to teraherz (THz) metasurfaces using THz time domain spectroscopy. Complementary THz split ring resonator (cSRR) arrays are used as metasurfaces[4]. A higher coupling rate can be achieved by reducing the capacitive gap of the resonator due to the increased vacuum ?eld ?uctuations. However, our results indicate that this reduction introduces an inhomogenous broadening of the upper polariton branch below a threshold gap width.
关键词： complementary split ring resonator,Ultrastrong coupling,Landau level transitions,THz time domain spectroscopy,THz metasurfaces
更新于2025-09-12 10:27:22
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The New Concept of Nano-Device Spectroscopy Based on Rabi–Bloch Oscillations for THz-Frequency Range
摘要： We considered one-dimensional quantum chains of two-level Fermi particles coupled via the tunneling driven both by ac and dc ?elds in the regimes of strong and ultrastrong coupling. The frequency of ac ?eld is matched with the frequency of the quantum transition. Based on the fundamental principles of electrodynamics and quantum theory, we developed a general model of quantum dynamics for such interactions. We showed that the joint action of ac and dc ?elds leads to the strong mutual in?uence of Rabi- and Bloch oscillations, one to another. We focused on the regime of ultrastrong coupling, for which Bloch- and Rabi-frequencies are signi?cant values of the frequency of interband transition. The Hamiltonian was solved numerically, with account of anti-resonant terms. It manifests by the appearance of a great number of narrow high-amplitude resonant lines in the spectra of tunneling current and dipole moment. We proposed the new concept of terahertz (THz) spectroscopy, which is promising for different applications in future nanoelectronics and nano-photonics.
关键词： ultrastrong coupling,Bloch-oscillations,THz-spectroscopy,Rabi-oscillations
更新于2025-09-11 14:12:44
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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