Multiple-quantum transitions and charge-induced decoherence of donor   nuclear spins in silicon
  We study single- and multi-quantum transitions of the nuclear spins of ionized arsenic donors in silicon and find quadrupolar effects on the coherence times, which we link to fluctuating electrical field gradients present after the application of light and bias voltage pulses. To determine the coherence times of superpositions of all orders in the 4-dimensional Hilbert space, we use a phase-cycling technique and find that, when electrical effects were allowed to decay, these times scale as expected for a field-like decoherence mechanism such as the interaction with surrounding $^{29}$Si nuclear spins. 
David P. Franke, Moritz P. D. Pfl\"uger, Kohei M. Itoh, Martin S.   Brandt
quant-ph cond-mat.mtrl-sci