Quantum dots can emit single photons, entangled photons and indistinguishable photons which makes them a versatile platform for building quantum technologies. In all cases the purity of the light from the quantum dots can be improved by judicious choice of the excitation mechanism used to create light from the dot. The most promising scheme is to use resonant excitation, that is, laser excitation at the same energy as the transition to give the greatest purity of photon emission.
Semiconductor quantum dots integrated within monolithic microcavities [1,2] are a promising technology in this regard as their resonant excitation can deliver coherent single photons with high efficiency. We have shown that the resonant scattering of light from a pillar microcavity containing a single quantum dot can lead to highly indistinguishable photons.
We have also shown that the reflectivity of the cavity can be different depending on whether one of two photons is incident upon it. We have used this effect to “sort” photons, sending light that contains different numbers of photons into different optical modes .
Cartoon of the photon sorter, which can either reflect single photons (blue), or can be tuned to reflect only multi-photon states (red).