title: Coherence of an entangled exciton-photon state.
abstract: We study the effect of the exciton fine-structure splitting on the polarization entanglement of photon pairs produced by the biexciton cascade in a quantum dot. Entanglement persists despite separations between the intermediate energy levels of up to 4 microeV. Measurements show that entanglement of the photon pair is robust to the dephasing of the intermediate exciton state responsible for the first-order coherence time of either single photon. We present a theoretical framework incorporating the effects of spin scattering, background light, and dephasing. We distinguish between the first-order coherence time, and a parameter which we measure for the first time and define as the cross-coherence time.
authors.affiliation: Toshiba Research Europe Limited, 208 Cambridge Science Park, Cambridge CB4 0GZ, United Kingdom.
authors.forename: A J
authors.initials: AJ
authors.lastname: Hudson
authors.forename: R M
authors.initials: RM
authors.lastname: Stevenson
authors.forename: A J
authors.initials: AJ
authors.lastname: Bennett
authors.forename: R J
authors.initials: RJ
authors.lastname: Young
authors.forename: C A
authors.initials: CA
authors.lastname: Nicoll
authors.forename: P
authors.initials: P
authors.lastname: Atkinson
authors.forename: K
authors.initials: K
authors.lastname: Cooper
authors.forename: D A
authors.initials: DA
authors.lastname: Ritchie
authors.forename: A J
authors.initials: AJ
authors.lastname: Shields