We report the experimental observation of photon antibunching in fluorescen
ce from a single self-assembled InAs quantum dot. The nonclassical photon s
tatistics proves the atomlike nature of a single quantum dot at cryogenic t
emperatures. Pump-power-dependent measurements of the correlation function
g((2))(tau) provide a method to determine the recombination time of the sin
gle exciton ground-state transition that does not require pulsed lasers. Us
ing this method, we investigate the influence of photonic environment on a
single quantum dot exciton lifetime.