Photon beats from a single semiconductor quantum dot

Single-photon interference is observed on the ultranarrow long-term stable exciton resonance of an individual semiconductor quantum dot. This interfer ence is related to the fine-structure splitting and allows direct conclusio ns about the coherence properties of the exciton. When selectively addressi ng a particular dot by quasiresonant phonon-assisted excitation, despite a rapid orientation relaxation on a I-ps time scale, coherence is partly main tained. No significant further decoherence occurs when the ground state is reached until the exciton recombines radiatively (approximate to 300 ps).