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

Abstract

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