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Biphoton interference and coherence of a quantum dot source of entangled photons

Research output: Contribution to conference - Without ISBN/ISSN Abstract

Published
Publication date15/11/2011
<mark>Original language</mark>English
EventSecond international workshop on: Positioning of single nanostructures - single quantum devices - Germany, Lauterbad, United Kingdom
Duration: 15/11/2007 → …

Conference

ConferenceSecond international workshop on: Positioning of single nanostructures - single quantum devices
CountryUnited Kingdom
CityLauterbad
Period15/11/07 → …

Abstract

A well controlled, triggered source of entangled photons is desirable for many applications in quantum information processing. The two-photon cascade from a biexciton state, two electrons and holes, confined in a quantum dot can be such a source of polarisation-entangled photons provided the two decay paths from the biexciton carry no “which-path” information. In recent years many techniques have been employed to make the two optical decay paths from the biexciton state indistinguishable. A number of these techniques will be discussed and entangled-photon emission from a single quantum dot with a high fidelity in the expected Bell-state from the cascade will be demonstrated.

This source of entangled photons allows optical interferometry beyond the limits imposed by the photon wavelength. Interference fringes of the entangled biphoton state reveals a periodicity half of that obtained with the single photon, and much less than that of the pump laser. High fringe visibility indicates that biphoton interference is less sensitive to decoherence than interference of two sequential single photons.

The effect of the exciton fine-structure splitting on our entangled photon source will be shown. Surprisingly the entanglement is found to persist despite relatively large separations between the intermediate energy levels of up to 4µeV. Measurements demonstrate 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 distinguish between the first-order coherence time, and a parameter defined as the cross-coherence time, this is illustrated in the figure.