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.
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