Electron spin relaxation due to charge noise

Abstract

We study decoherence of an electron spin qubit in a quantum dot due to charge noise. We find that at the lowest order, the pure dephasing channel is suppressed for both 1/f charge noise and Johnson noise, so that charge noise leads to a pure relaxation channel of decoherence. Because of the weaker magnetic field dependence, the spin relaxation rate due to charge noise could dominate over phonon noise at low magnetic fields in a gate-defined GaAs or Si quantum dot or a InAs self-assembled quantum dot. Furthermore, in a large InAs self-assembled quantum dot, the spin relaxation rate due to phonon noise could be suppressed in high magnetic field, and the spin relaxation due to charge noise could dominate in both low and high magnetic field. Numerically, in a 1 Tesla field, the spin relaxation time due to typical charge noise is about 100 s in Si, 0.1 s in GaAs for a gate-defined quantum dot with a 1 meV confinement, and 10 µs in InAs self-assembled quantum dot with a 4 meV confinement.

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

“…This reduction in the effective coupling strength causes the spin relaxation rate to decrease from the B 7 0 curve in Fig. 4, and it could even lead to a suppression of spin relaxation, 33 as has been observed experimentally for a spin singlettriplet qubit. 50 Quantitatively, the relaxation time due to phonon noise is ∼ 100 s in a 1 Tesla field, and ∼ 0.1 ms in a 10 Tesla field.…”

“…For comparison, we include in our discussion below spin relaxation due to intra-valley SO mixing (higher energy p-orbitals are involved), which has been studied extensively in the literature, especially for spin qubit in GaAs QD. 9,[33][34][35][39][40][41][42][43][44][45] For spin qubit in Si QD, this intra-valley SO mixing induced spin relaxation is also present, and is important in high B-field due to the stronger B-field dependence. 33,34 We use the existing results in the literature, and the corresponding spin relaxation rate is [33][34][35] …”

“…The relaxation rate through the intra-valley SO mixing is dominant in the high-magneticfield regime, which shows a B 7 0 dependence before the phonon bottleneck takes effect and the curves bend downward from the B 7 0 line. [33][34][35] The phonon bottleneck effect is due to the averaging of electron-phonon interaction matrix element for high-frequency phonons. This reduction in the effective coupling strength causes the spin relaxation rate to decrease from the B 7 0 curve in Fig.…”

“…9, we have F SO = α 2 + . 33 In a general calculation of spin relaxation in a Si QD, both spin relaxation mechanisms, namely relaxation due to spin-valley mixing (Γ SV ) and relaxation due to intra-valley SO mixing (Γ SO ), need to be accounted for. We consider both in our calculations below in order to achieve a comprehensive understanding of spin relaxation.…”

“…Spin relaxation could come directly from magnetic noise in the environment, or from electrical noise via spin-orbit or exchange interaction. Indeed, for a single spin in a quantum dot, we have shown 33 that electrical noise from the circuits or surrounding traps could be an important cause for spin relaxation, particularly at a smaller qubit energy splitting. In this previous study, however, we only considered intra-valley orbital dynamics for an electron in Si.…”