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We demonstrate that a ionising transition can be strongly coupled to a photonic resonance. The strong coupling manifests itself with the appearance of a narrow optically active resonance below the ionisation threshold. Such a resonance is due to electrons transitioning into a novel bound state created by the collective coupling of the electron gas with the vacuum field of the photonic resonator. Applying our theory to the case of bound-to-continuum transitions in microcavity-embedded doped quantum wells, we show how those strong-coupling features can be exploited as a novel knob to tune both optical and electronic properties of semiconductor heterostructures.
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Achieving cavity-optomechanical strong coupling with high-frequency phonons provides a rich avenue for quantum technology development including quantum state-transfer, memory, and transduction, as well as enabling several fundamental studies of macroscopic phononic degrees-of-freedom. Reaching such coupling with GHz mechanical modes however has proved challenging, with a prominent hindrance being material- and surface-induced-optical absorption in many materials. Here, we circumvent these challenges and report the observation of optomechanical strong coupling to a high frequency (11 GHz) mechanical mode of a fused-silica whispering-gallery microresonator via the electrostrictive Brillouin interaction. Using an optical heterodyne detection scheme, the anti-Stokes light backscattered from the resonator is measured and normal-mode splitting and an avoided crossing are observed in the recorded spectra, providing unambiguous signatures of strong coupling. The optomechanical coupling rate reaches values as high as $G/2pi = 39 text{MHz}$ through the use of an auxiliary pump resonance, where the coupling dominates both the optical ($kappa/2pi = 3 text{MHz}$) and the mechanical ($gamma_text{m}/2pi = 21 text{MHz}$) amplitude decay rates. Our findings provide a promising new approach for optical quantum control using light and sound.
The relaxation of a quantum emitter (QE) near metal-dielectric layered nanostructures is investigated, with focus on the influence of plasmonic quantum effects. The Greens tensor approach, combined with the Feibelman $d$-parameter formalism, is used to calculate the Purcell factor and the dynamics of a two-level QE in the presence of the nanostructure. Focusing on the case of Na, we identify electron spill-out as the dominant source of quantum effects in jellium-like metals. Our results reveal a clear splitting in the emission spectrum of the emitter, and non-Markovian relaxation dynamics, implying strong light--matter coupling between them, a coupling that is not prevented by the quantum-informed optical response of the metal.
The strong coupling between two subsystems consisting of quantum emitters and photonic modes, at which the level splitting of mixed quantum states occurs, has been a central subject of quantum physics and nanophotonics due to various important applications. The spectral Rabi-splitting of photon emission or absorption has been adopted to experimentally characterize the strong coupling under the equality assumption that it is identical to the level splitting. Here, we for the first time reveal that the equality assumption is not valid. It is the invalidity that results in the relativity and diversity of the strong coupling characterized by the spectral Rabi-splitting to the measured subsystems, highly correlated with their dissipative decays. The strong coupling is easier to be observed from the subsystem with larger decay, and can be classified into pseudo-, dark-, middle-, and super-strong interaction regimes. We also suggest a prototype of coupled plasmon-exciton system for possibly future experiment observations on these novel predictions. Our work brings new fundamental insight to the light-matter interaction in nanostructures, which will stimulate further researches in this field.
The regime of strong light-matter coupling is typically associated with weak excitation. With current realizations of cavity-QED systems, strong coupling may persevere even at elevated excitation levels sufficient to cross the threshold to lasing. In the presence of stimulated emission, the vacuum-Rabi doublet in the emission spectrum is modified and the established criterion for strong coupling no longer applies. We provide a generalized criterion for strong coupling and the corresponding emission spectrum, which includes the influence of higher Jaynes-Cummings states. The applicability is demonstrated in a theory-experiment comparison of a few-emitter quantum-dot--micropillar laser as a particular realization of the driven dissipative Jaynes-Cummings model. Furthermore, we address the question if and for which parameters true single-emitter lasing can be achieved, and provide evidence for the coexistence of strong coupling and lasing in our system in the presence of background emitter contributions.
We present a method to control the resonant coupling interaction in a coupled-cavity photonic crystal molecule by using a local and reversible photochromic tuning technique. We demonstrate the ability to tune both a two-cavity and a three-cavity photonic crystal molecule through the resonance condition by selectively tuning the individual cavities. Using this technique, we can quantitatively determine important parameters of the coupled-cavity system such as the photon tunneling rate. This method can be scaled to photonic crystal molecules with larger numbers of cavities, which provides a versatile method for studying strong interactions in coupled resonator arrays.
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