Spin Relaxation in Si/SiGe Quantum Dot Devices with Micromagnets*

Recent quantum control experiments in Si/SiGe quantum dots utilizing a micromagnet for electrically driven spin resonance have reported spin relaxation times (T₁) ranging from 4 ms to more than 50 ms [1,2]. These T₁ times are shorter than those obtained on samples without micromagnets, which suggests that the presence of the micromagnet is limiting T₁ [3,4]. We measure T₁ in a Si/SiGe device incorporating a micromagnet up to a magnetic field of 6 T. We find a saturation of T₁ at low fields, evidence of a valley relaxation hotspot, and a soft B³ field dependence above 2 T. These measurements indicate that the spin-orbit coupling induced by the micromagnet causes otherwise suppressed relaxation channels to dominate and limit qubit performance.

[1] Zajac et al., arXiv:1708.03530
[2] Watson et al., arXiv:1708.04214
[3] Hayes et al., arXiv:0908.0173
[4] Yang et al., Nature Comm. 4 2069 (2013)