Fast optical control of a coherent hole spin in a microcavity

Many of the most promising quantum information platforms store quantum information in electronic or atomic spins. To incorporate these devices into quantum networks, a spin–photon interface is required. Currently, the best on-demand single-photon sources use a semiconductor quantum dot in an engineered photonic environment. However, it is difficult to achieve coherent spin control in a high-performance single-photon source, and spin coherence is limited by magnetic noise from nuclear spins in the semiconductor host material. Here we combine all-optical spin control with a quantum dot in an open microcavity. We demonstrate fast coherent rotations of a hole spin around an arbitrary axis of the Bloch sphere with a maximum π-pulse fidelity of 98.6%. To suppress the slow magnetic noise, we laser cool the nuclear spins using the hole as a central spin. This extends the hole spin free-induction-decay time by more than an order of magnitude. It becomes much larger than both rotation time and radiative recombination time of the spin, enabling the creation of many spin–photon pairs before the loss of spin coherence. Spin–photon interfaces provide a connection between quantum information stored in atomic or electronic spins and optical communications networks. A quantum photon emitter with long-lived, controllable coherent spin has now been demonstrated.