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Donor electron spins in phosphorus-doped silicon (Si: P) are a candidate two-level system (qubit) for quantum information processing. Spin echo measurements of isotopically purified ^28Si: P are presented that show exceptionally long transverse relaxation (decoherence) times, T₂, at low temperature. Below 10K the spin decoherence is shown to be controlled by instantaneous diffusion and at higher temperatures by an Orbach process. T₂ for small pulse turning angles is 14 ms at 7 K and extrapolates to 60ms for an isolated spin, over 2 orders of magnitude longer than previously demonstrated.
Tyryshkin et al. (Thu,) studied this question.