Single Quantum Dot-cavity System Research Articles

Surface-passivated high-Q GaAs photonic crystal nanocavity with quantum dots

Photonic crystal (PhC) nanocavities with high quality (Q) factors have attracted much attention because of their strong spatial and temporal light confinement capability. The resulting enhanced light–matter interactions are beneficial for diverse photonic applications, ranging from on-chip optical communications to sensing. However, currently achievable Q factors for active PhC nanocavities, which embed active emitters inside, are much lower than those of the passive structures because of large optical loss, presumably originating from light scattering by structural imperfections and/or optical absorptions. Here, we demonstrate a significant improvement of Q factors up to ∼160 000 in GaAs active PhC nanocavities using a sulfur-based surface passivation technique. This value is the highest ever reported for any active PhC nanocavities with semiconductor quantum dots. The surface-passivated cavities also exhibit reduced variation in both Q factors and cavity resonant wavelengths. We find that the improvement in the cavity performance presumably arises from suppressed light absorption at the surface of the PhC’s host material by performing a set of PL measurements in spectral and time domains. With the surface passivation technique, we also demonstrate a strongly coupled single quantum dot-cavity system based on a PhC nanocavity with a high Q factor of ∼100 000. These results will pave the way for advanced quantum dot-based cavity quantum electrodynamics and GaAs micro/nanophotonic applications containing active emitters.

Deterministic single-photon subtraction based on a coupled single quantum dot-cavity system.

We present a scheme for realizing deterministic single-photon subtraction in a coupled single quantum dot-cavity solid-state system. The device consists of a charged quantum dot and its coupled bimodal photonic crystal cavity with a moderate magnetic field applied in a Voigt configuration. We numerically simulate injection of optical pulses into one of the cavity modes and show that the system deterministically transfers one photon into the second cavity mode for input pulses in the form of both Fock states and coherent states. This device has potential in the application of a compact and integrated solid-state based device for quantum information processing.

Quantum interference induced photon blockade in a coupled single quantum dot-cavity system.

We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g(2)(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing.

Lasing properties of non-resonant single quantum dot-cavity system under incoherent excitation

Single quantum dot laser has earned extensive interest due to its peculiar properties, however, most of works are focused on the resonant case. In this paper, the lasing oscillation based on off-resonant quantum dot (QD)-cavity system is investigated detailedly through two-electrons QD model. By gradually increasing the pump rate, the typical lasing signatures are shown with and without detuning, include the spectral transition from multiple peaks to single peak, and antibunching to Poissonian distribution. It is also demonstrated how detuning factor strongly influence photon statistics and emission properties, specially, the side peak of spectra induced by the exchange energy (named "sub-peak") will go across the main peak from left to right when the detuning is gradually increased, and, furthermore, we find the "sub-peak cross of spectra" will facilitate the lasing oscillation because of the existence of exchange energy.

Giant Rabi splitting in a metallic cluster–cavity system

We theoretically investigate the photoabsorption cross-section of a cluster of alkali atoms embedded in a single-mode quantum microcavity. We show that if the energy of the giant plasmonic resonance lies close to the energy of the cavity mode, the strong coupling between the plasmon and cavity photon can occur which is characterized by mode anticrossing and observation of the doublet structure in the photoabsorption spectrum. The characteristic values of the Rabi splitting are expected to be several orders of magnitude larger than those observed in single quantum dot–cavity systems.

Deterministic emitter-cavity coupling using a single-site controlled quantum dot

Site-selective epitaxy is used to deterministically control the nucleation site of a single quantum dot. A photonic crystal cavity is fabricated at the dot site for a true single quantum dot-cavity system which, by design, contains no background emitters. Cavity tuning at fixed temperature is used to measure the dot-cavity coupling over a large $(g15\text{ }\text{meV})$ detuning range using nonresonant excitation. The low-excitation spectra are modeled using a master equation model based on incoherent excitation. We find that pure phonon dephasing alone does not account for the observed nonresonant cavity emission and an additional cavity feeding mechanism, consistent with phonon-assisted dot-cavity coupling, must be included to reproduce the experimental spectra.

Laser oscillation in a strongly coupled single-quantum-dot–nanocavity system

The strong coupling of photons and matter1 in semiconductor nanocavities has been a test bed for cavity quantum electrodynamics2,3 (QED). Vacuum Rabi oscillation4,5,6,7,8—the coherent exchange of a single quantum between a single quantum dot (SQD) and an optical cavity—and highly efficient cavity-QED lasers9,10,11,12,13,14,15,16,17,18,19 have both been reported. The coexistence of vacuum Rabi oscillation and laser oscillation seems to be contradictory, but it has recently been predicted theoretically that the strong-coupling effect could be sustained in laser oscillation20. Here, we demonstrate the onset of lasing in the strong-coupling regime in an SQD–cavity system. A high-quality semiconductor optical nanocavity and strong SQD–field coupling enabled the onset of lasing while maintaining the fragile coherent exchange of quanta.