1302.1709 (S. J. Balian et al.)

Theoretical analysis of spin qubit decoherence near optimal working
points    [PDF]

S. J. Balian, T. S. Monteiro

We investigate suppression of various decoherence mechanisms at critical points variously termed optimal working points (OWPs) or clock transitions (CTs) of electron paramagnetic resonance (EPR) transitions in Si-based spin qubits, where the frequency -- field gradient is zero ($df/dB=0$). New experiments by Wolfowicz {\it et al.} [arXiv:1301.6567 (2013)] have demonstrated suppression of both instantaneous diffusion, as well as spin diffusion at these points, yielding orders of magnitude enhancement in coherence times: up to seconds, without extrapolation to zero-duration pulses as was until now necessary. We obtain simple analytical expressions and compare with full numerics, explaining the form of decoherence suppression for bismuth donors in Si (Si:Bi). It is demonstrated that behavior at the OWPs cannot be fully analyzed in terms of the behavior of $df/dB$, especially in the case of spin diffusion, indicating the need for an understanding at the level of the underlying microscopic processes entangling the central spin system and the spin bath.

View original: http://arxiv.org/abs/1302.1709