Spin relaxation in a Si quantum dot due to spin-valley mixing

摘要

We study the relaxation of an electron spin qubit in a Si quantum dot due toelectrical noise. In particular, we clarify how the presence of conduction-bandvalleys influences spin relaxation. In single-valley semiconductor quantumdots, spin relaxation is through the mixing of spin and envelope orbital statesvia spin-orbit interaction. In Si, the relaxation could also be through themixing of spin and valley states. We find that the additional spin relaxationchannel, via spin-valley mixing and electrical noise, is indeed important foran electron spin in a Si quantum dot. By considering both spin-valley andintravalley spin-orbit mixings and Johnson noise in a Si device, we find thatthe spin relaxation rate peaks at the hot spot, where the Zeeman splittingmatches the valley splitting. Furthermore, because of a weaker fielddependence, the spin relaxation rate due to Johnson noise could dominate overphonon noise at low magnetic fields, which fits well with recent experiments.