We use the nuclear spin coherence of 31P donors in 28Si to determine flip-flop rates of donor electron spins. Isotopically purified 28Si crystals minimize the number of 29Si flip-flops, and measurements at 1.7 K suppress electron spin relaxation. The crystals have donor concentrations ranging from 1.2 × 1014 to 3.3 × 1015 P/cm3, allowing us to detect how electron flip-flop rates change with donor density. We also simulate how electron spin flip-flops can cause nuclear spin decoherence. We find that when these flip-flops are the primary cause of decoherence, Hahn echo decays have a stretched exponential form. For our two higher donor density crystals (> 1015 P/cm3), there is excellent agreement between simulations and experiments. In lower density crystals (< 1015 P/cm3), there is no longer agreement between simulations and experiments, suggesting a different, unknown mechanism is limiting nuclear spin coherence. The nuclear spin coherence in the lowest density crystal (1.2 × 1014 P/cm3) allows us to place upper bounds on the magnitude of noise sources in bulk crystals such as electric field fluctuations that may degrade silicon quantum devices.
|Publication status||Published - 2017 Sep 8|
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