We investigate the evolution of quantum correlations over the lifetime of a multi-photon state. Measurements reveal time-dependent oscillations of the entanglement fidelity for photon pairs created by a single semiconductor quantum dot. The oscillations are attributed to the phase acquired in the intermediate, non-degenerate, exciton-photon state and are consistent with simulations. We conclude that emission of photon pairs by a typical quantum dot with finite polarisation splitting is in fact entangled in a time-evolving state, and not classically correlated as previously regarded.
@article{arxiv.0803.3947,
title = {Evolution of entanglement within classical light states},
author = {R. Mark Stevenson and Andrew J. Hudson and Anthony J. Bennett and Robert J. Young and Christine A. Nicoll and David A. Ritchie and Andrew J. Shields},
journal= {arXiv preprint arXiv:0803.3947},
year = {2009}
}