A quantum-dot-based single-photon source //

A semiconductor quantum dot is a potentially excellent source of coherent single photons. To be useful, the noise in the semiconductor host must be addressed –
noise in the semiconductor results in noisy photons – and some photonic engineering must be carried out in order to put the photons into one optical mode. Some success has been achieved using low-noise heterostructures in an open microcavity [N. Tomm et al., Nature Nanotechnology 16, 399 (2021)]. The source has an end-to-end efficiency of about 60%, and the coherence of the photons (as judged by the visibility of two-photon interference) is 98%. To create more complex photonic states, entangled pairs and cluster states, the spin of a single electron (or hole) trapped in the quantum dot can be exploited. The Achilles heel of the quantum dot system is the poor spin coherence. This weakness has now been addressed via quantum control of the environment, specifically, laser-cooling the nuclear spins. The talk will introduce the quantum dot system, describe recent results, and present some prospects for the future.

Richard Warburton leads the Nano-Photonics Group at the University of Basel