Signatures of the ultrastrong light-matter coupling regime

Abstract

In a microcavity, light-matter coupling is quantified by the vacuum-Rabi frequency Omega_R. When Omega_R is larger than radiative and nonradiative loss rates, the system eigenstates (polaritons) are linear superposition of photonic and electronic excitations, a condition actively investigated in diverse physical implementations. Recently, a quantum electrodynamic regime (ultrastrong coupling) was predicted when Omega_R becomes comparable to the transition frequency. Here we report signatures of this regime in a quantum-well intersubband microcavity. Measuring the cavity-polariton dispersion in a room-temperature linear optical experiment, we directly observe the antiresonant light-matter coupling and the photon-energy renormalization of the vacuum field

Quasi-Bell states in a strongly coupled qubit–oscillator system and their delocalization in the phase space

“…Recently, however, a variety of experimental situations pertaining to the stronger coupling domain, where the rotating wave approximation no longer holds, have been investigated. Various experimental realizations such as a nanomechanical resonator capacitively coupled to a Cooper-pair box [2], a quantum semiconductor microcavity undergoing excitonic transitions [3], a flux-biased superconducting quantum circuit that uses large nonlinear inductance of the Josephson junctions to achieve ultrastrong coupling with a coplanar waveguide resonator [4] have been achieved. The superconducting circuits based on the Josephson junctions behave, in certain parametric range, as effective two level systems, and can exhibit macroscopic quantum coherence [5,6].…”

Circuit quantum electrodynamics in the ultrastrong-coupling regime

“…Although the Hamiltonian of a realistic atom-cavity system contains so-called counterrotating terms allowing the simultaneous creation ior annihilation of an excitation in both atom and cavity mode, these terms can be safely neglected for small normalized coupling rates g/ω r . However, when g becomes a significant fraction of ω r , the counterrotating terms are expected to manifest, giving rise to exciting effects in QED.The ultrastrong coupling regime is difficult to reach in traditional quantum optics, but was recently realized in a solid-state semiconductor system 19,20 . There, quantitative deviations from the Jaynes-Cummings model have been observed, but a direct experimental proof of its breakdown by means of an unambiguous feature is still missing.…”

“…The ultrastrong coupling regime is difficult to reach in traditional quantum optics, but was recently realized in a solid-state semiconductor system 19,20 . There, quantitative deviations from the Jaynes-Cummings model have been observed, but a direct experimental proof of its breakdown by means of an unambiguous feature is still missing.…”

“…While these experiments are well described by the renowned Jaynes-Cummings model 16 , novel physics is expected when g reaches a considerable fraction of ωr. Promising steps towards this so-called ultrastrong coupling regime 17,18 have recently been taken in semiconductor structures 19,20 . Here, we report on the first experimental realization of a superconducting circuit QED system in the ultrastrong coupling limit and present direct evidence for the breakdown of the Jaynes-Cummings model.…”

Ultrastrong coupling of intersubband plasmons and terahertz metamaterials

“…[1][2][3][4][5][6][7] Due to the highly sub-wavelength confinement of the electromagnetic field, coupling strengths as high as 27% of the unperturbed frequency of the quantum system have been reached using LC cavities. 6 This so-called ultrastrong coupling regime 8 is very interesting both for the investigation of remarkable cavity QED effects, like the generation of quantum vacuum radiation, 9 as well as for applications, such as terahertz (THz) lasing at room-temperature.…”