A Self-assembled Quantum Dot as Single Photon Source and Spin Qubit: Charge Noise and Spin Noise

Abstract

A self-assembled quantum dot confines both electrons and holes to a nano-sized region inside a semiconductor. An exciton in a single self-assembled quantum dot is a potentially excellent source of single photons. A quantum dot also acts as a host for a spin qubit with the advantage that the spin can be initialized, manipulated and read-out with optical techniques. However, the exciton and spins couple strongly not just to an external optical probe but also to internal excitations of the host semiconductor: the semiconductor is a source of noise resulting in exciton and spin dephasing. The noise can be suppressed in some cases, circumvented in others, leading to an improvement in quantum dot performance. In particular, resonant excitation at low temperature using high quality material results in a small level of charge noise . A heavy hole spin in an in-plane magnetic field is decoupled from the spin noise arising from fluctuations in the nuclear spin bath. Presented here is a series of experiments which probe the noise in advanced quantum dot devices: single quantum dot resonance fluorescence as a sensor of both charge noise and spin noise ; nuclear magnetic resonance on the quantum dot nuclear spins to probe the electron spin hyperfine interaction ; and coherent population trapping to probe the hole spin hyperfine interaction .