injection current. Pulsed electrical injection leads to pulsed emision from the dot, with a single photon in each pulse, provided that the pulse width is much less than the exciton lifetime. The second order correlation function recorded for theXlinewithapulsewidthof400ps(Fig,ZB(i)) shows a strongly suppressed peak at zero time delay, indicating a strong suppression of the multi-photon emission pulses from the dot. This contrasts with the pair correlation recorded for the wetting layer electroluminescence (Fig.

Polarization correlation in a linear basis, but not entanglement, is observed between the biexciton and single-exciton photons emitted by a single InAs quantum dot in a two-photon cascade. The results are well described quantitatively by a probabilistic model that includes two decay paths for a biexciton through a nondegenerate pair of one-exciton states, with the polarization of the emitted photons depending on the decay path. The results show that spin nondegeneracy due to quantum-dot asymmetry is a significant obstacle to the realization of an entangled-photon generation device.