Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures

TL;DR

This paper demonstrates significantly extended spin coherence times in hole spins within GaAs/AlGaAs quantum wells at very low temperatures, advancing the potential for scalable quantum computing with semiconductor spins.

Contribution

It reports a breakthrough in achieving long coherence times for hole spins in natural quantum dots at sub-500 mK temperatures, using advanced optical techniques.

Findings

Hole-spin coherence times exceed 70 ns at low magnetic fields

Optical initialization and spin dynamics are well modeled by rate equations

Longer coherence times improve prospects for quantum information processing

Abstract

For the realisation of scalable solid-state quantum-bit systems, spins in semiconductor quantum dots are promising candidates. A key requirement for quantum logic operations is a sufficiently long coherence time of the spin system. Recently, hole spins in III-V-based quantum dots were discussed as alternatives to electron spins, since the hole spin, in contrast to the electron spin, is not affected by contact hyperfine interaction with the nuclear spins. Here, we report a breakthrough in the spin coherence times of hole ensembles, confined in so called natural quantum dots, in narrow GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently, time-resolved Faraday rotation and resonant spin amplification techniques deliver hole-spin coherence times, which approach in the low magnetic field limit values above 70 ns. The optical initialisation of the hole spin polarisation, as well as the interconnected electron and hole spin dynamics in our samples are well reproduced using a rate equation model.