Resonance fluorescence of a strongly driven two-level system with dynamically modulated frequency

When a two-level atom interacts with a strong optical field, its bare states are split into doublets or "dressed states" separated by the Rabi frequency. This phenomenon gives rise to the Mollow triplet in the resonance fluorescence spectrum, a fundamental phenomenon in quantum optics. Beyond the Mollow triplet, new physics emerges when a two-level system is subjected to bichromatic or polychromatic driving fields, leading to diverse nonlinear and multiphoton dynamics in the interaction between light and matter. In this talk, I will present the first experimental study of the resonance fluorescence when a radio-frequency field is strongly driving the transition between two atom-light dressed states of the same energy ladder. We employ a single self-assembled InAs quantum dot as the two-level system. The quantum dot is simultaneously driven by a laser near resonant with its optical transition and a surface acoustic wave near resonant with the optical Rabi frequency. We observe emission spectra significantly altered from the standard Mollow triplet, including the dynamical cancellation of the spontaneous emission at the atomic frequency, a feature previously seen only with bichromatic optical driving. The observed spectra are well explained by a theoretical model incorporating the hybridization of the atom, optical field, and acoustic field. Beyond its significance in quantum optics, our device enables the optical cooling of acoustic phonons mediated by a single two-level system. By measuring the full emission spectrum of the doubly dressed quantum dot under various laser amplitudes and detuning, we experimentally explored the optimal conditions for phonon cooling. Our results provide new insights into quantum interactions among single atoms, light, and sound in the strong driving limit, paving the way for advances in nonclassical light and sound generation, quantum transduction, and hybrid quantum systems.