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arXiv:quant-ph/0601187 · New Journal of Physics

Improved fidelity of triggered entangled photons from single quantum dots

Robert James Young, R. M. Stevenson, P. Atkinson, Ken Cooper, D. A. Ritchie, Andrew J. Shields

Published Feb 23, 2006• 285 citations
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Abstract

We demonstrate the triggered emission of polarization-entangled photon pairs from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs planar microcavity. Improvements in the sample design blue shifts the wetting layer to reduce the contribution of background light in the measurements. Results presented show that >70% of the detected photon pairs are entangled. The high fidelity of the state that we determine is sufficient to satisfy numerous tests for entanglement. The improved quality of entanglement represents a significant step towards the realization of a practical quantum dot source compatible with applications in quantum information.

DOI
10.1088/1367-2630/8/2/029

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We demonstrate the triggered emission of polarization-entangled photon pairs from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs planar microcavity. Improvements in the sample design blue shifts the wetting layer to reduce the contribution of background light in the measurements. Results presented show that >70% of the detected photon pairs are entangled. The high fidelity of the state that we determine is sufficient to satisfy numerous tests for entanglement. The improved quality of entanglement represents a significant step towards the realization of a practical quantum dot source compatible with applications in quantum information.
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For scalable applications of optical quantum information it is desirable to have a well controlled source of photons, producing single photons or entangled-pairs on-demand. The finite delay following decay of an exciton confined in a quantum dot makes them a good source of single photons, we demonstrate this, triggering the emission with a pulsed laser. Currently the most widely used techniques for generating entangled photon pairs are nonlinear optical processes, such as parametric down conversion, which produces a probabilistic number of pairs per excitation cycle. Such a source is of limited use in quantum information/processing applications where a regular stream of single entangled photon pairs is preferable. We produced such a triggered source from a semiconductor device for the first time, using the two-photon cascade from a biexciton confined in a single quantum dot. We demonstrate a fidelity of 70% for the emission from the biexciton cascade to the expected bell state. Single quantum dots could prove to be the first robust and compact triggered source of entangled photons.