Quantum communication relies on the availability of light pulses with strong quantum correlations among photons. An example of such an optical source is a single-photon pulse with a vanishing probability for detecting two or more photons. Using pulsed laser excitation of a single quantum dot, a single-photon turnstile device that generates a train of single-photon pulses was demonstrated. For a spectrally isolated quantum dot, nearly 100% of the excitation pulses lead to emission of a single photon, yielding an ideal single-photon source.

An optical source that produces single-photon pulses on demand has potential applications in linear optics quantum computation, provided that stringent requirements on indistinguishability and collection efficiency of the generated photons are met. We show that these are conflicting requirements for anharmonic emitters that are incoherently pumped via reservoirs. As a model for a coherently pumped single photon source, we propose cavity-assisted spin-flip Raman transitions in a single electron charged quantum dot embedded in a microcavity. We demonstrate that using such a source, arbitrarily high collection efficiency and indistinguishability of the generated photons can be obtained simultaneously with increased cavity coupling. We analyze the role of errors that arise from distinguishability of the single-photon pulses in linear optics quantum gates by relating the gate fidelity to the strength of the two-photon interference dip in photon cross-correlation measurements. We find that performing controlled phase operations with error $<1\%$ requires nanocavities with Purcell factors $F_P⩾40$ in the absence of dephasing, without necessitating the strong coupling limit.

We investigate cavity-quantum electrodynamics (QED) effects in an all-semiconductor nanostructure by tuning a single self-assembled InAs quantum dot (QD) into resonance with a high quality factor microdisk whispering gallery mode (WGM). The stronger temperature dependence of the QD single-exciton (1X) resonance allows us to change the relative energy of the WGM and the 1X transitions by varying the sample temperature. The two coupled resonances exhibit crossing behavior due to the weak coupling cavity-QED regime. We demonstrate exciton lifetime reduction by 6 due to the Purcell effect by tuning the QD into resonance with the WGM. Our experiments also show that single-exciton lifetime is independent of temperature up to 50 K.

We report optically pumped continuous-wave lasing from self-assembled InAs and InGaAs quantum dots (QDs) embedded in high-quality-factor microdisk laser structures. The microdisk emission spectra show lasing on 1–5 well separated modes in the wavelength range between 900 and 990 nm. The estimated threshold pump densities are between 20 and $\text{200\hspace{0.05em}}{\mathrm{W/cm}}^{\mathrm{2}}.$ The lasing characteristics are discussed in terms of both inhomogeneously and homogeneously broadened QD transitions.

We report the experimental observation of photon antibunching in fluorescence from a single self-assembled InAs quantum dot. The nonclassical photon statistics proves the atomlike nature of a single quantum dot at cryogenic temperatures. Pump-power-dependent measurements of the correlation function $g^{\mathrm{}\left(2\right)\mathrm{}}\left(\tau \right)$ provide a method to determine the recombination time of the single exciton ground-state transition that does not require pulsed lasers. Using this method, we investigate the influence of photonic environment on a single quantum dot exciton lifetime.

We report photon correlation measurements that reveal unique signatures of biexciton and charged exciton emissions in a single self-assembled InAs quantum dot. Biexciton emission exhibits both bunching and antibunching under continuous-wave excitation and only antibunching under pulsed excitation. Cross correlation between biexciton and single-exciton emissions reveals highly asymmetric features due to cascaded emission. Under our excitation conditions, no polarization correlations between the exciton and biexciton emissions were observed.