This study investigates the quantum nature of a strongly-coupled single quantum dot (QD)-cavity system. The researchers demonstrate that quantum information processing (QIP) tasks, such as controlled coherent coupling and entanglement, can be achieved in solid-state systems by coupling semiconductor QDs to monolithic optical cavities. They observe quantum correlations in photoluminescence (PL) from a photonic crystal (PC) nanocavity interacting with a single QD located at the cavity's electric field maximum. When off-resonant, photon emission from the cavity mode and QD excitons is anti-correlated at the level of single quanta, proving that the mode is driven solely by the QD. When tuned into resonance, the exciton and photon enter the strong-coupling regime of cavity-QED, and the QD lifetime reduces by a factor of 120. The photon stream from the cavity becomes antibunched, proving that the coupled exciton/photon system is in the quantum anharmonic regime. The study confirms that QIP tasks requiring the quantum nonlinear regime are achievable in the solid state. The researchers position a nanocavity with 30 nm accuracy to a single QD, aligning it to the electric-field maximum of the cavity mode. This technique allows for unprecedented clarity in studying the coupled system. The measured spectrum of the QD consists of narrow, isolated excitonic transitions, promising for nanocavity coupling. The PC is fabricated with lattice parameter and hole radius selected to tune the nanocavity mode to the precise spectral location of the QD. The cavity mode is spectrally positioned a few nanometers shorter in wavelength than the exciton transitions, allowing for tuning by a thin-film condensation technique. The study observes that even a single QD sustains efficient mode emission for all detunings observed in ~20 deterministically-coupled devices. The coupling is mediated by the QD, as opposed to bulk or wetting layer states. The researchers measure the quantum correlations between photons emitted from the exciton transitions and the spectrally detuned cavity. This measurement corresponds to the second-order, normally-ordered, cross-correlation function, revealing strong anti-bunching and proving the two emission events stem from the same single quantum emitter. The study confirms the strong coupling regime in the spectral domain, showing a spectral triplet in the strong coupling regime, unique among recent reports of solid-state vacuum Rabi splitting. The two outer peaks at Δλ = 0 are identified as the polariton states of the strongly coupled exciton-photon system. The measured spectra are compared to a calculated spectral function, showing good agreement with the measured ones. The study also confirms the strong coupling regime in the time domain, showing a reduction in the exciton lifetime by a factor of 120 when the cavity is tuned into resonance with the exciton. The reduction in lifetime confirms that the QDThis study investigates the quantum nature of a strongly-coupled single quantum dot (QD)-cavity system. The researchers demonstrate that quantum information processing (QIP) tasks, such as controlled coherent coupling and entanglement, can be achieved in solid-state systems by coupling semiconductor QDs to monolithic optical cavities. They observe quantum correlations in photoluminescence (PL) from a photonic crystal (PC) nanocavity interacting with a single QD located at the cavity's electric field maximum. When off-resonant, photon emission from the cavity mode and QD excitons is anti-correlated at the level of single quanta, proving that the mode is driven solely by the QD. When tuned into resonance, the exciton and photon enter the strong-coupling regime of cavity-QED, and the QD lifetime reduces by a factor of 120. The photon stream from the cavity becomes antibunched, proving that the coupled exciton/photon system is in the quantum anharmonic regime. The study confirms that QIP tasks requiring the quantum nonlinear regime are achievable in the solid state. The researchers position a nanocavity with 30 nm accuracy to a single QD, aligning it to the electric-field maximum of the cavity mode. This technique allows for unprecedented clarity in studying the coupled system. The measured spectrum of the QD consists of narrow, isolated excitonic transitions, promising for nanocavity coupling. The PC is fabricated with lattice parameter and hole radius selected to tune the nanocavity mode to the precise spectral location of the QD. The cavity mode is spectrally positioned a few nanometers shorter in wavelength than the exciton transitions, allowing for tuning by a thin-film condensation technique. The study observes that even a single QD sustains efficient mode emission for all detunings observed in ~20 deterministically-coupled devices. The coupling is mediated by the QD, as opposed to bulk or wetting layer states. The researchers measure the quantum correlations between photons emitted from the exciton transitions and the spectrally detuned cavity. This measurement corresponds to the second-order, normally-ordered, cross-correlation function, revealing strong anti-bunching and proving the two emission events stem from the same single quantum emitter. The study confirms the strong coupling regime in the spectral domain, showing a spectral triplet in the strong coupling regime, unique among recent reports of solid-state vacuum Rabi splitting. The two outer peaks at Δλ = 0 are identified as the polariton states of the strongly coupled exciton-photon system. The measured spectra are compared to a calculated spectral function, showing good agreement with the measured ones. The study also confirms the strong coupling regime in the time domain, showing a reduction in the exciton lifetime by a factor of 120 when the cavity is tuned into resonance with the exciton. The reduction in lifetime confirms that the QD