Relaxation and Readout Visibility of a Singlet-Triplet Qubit in an   Overhauser Field Gradient
  Using single-shot charge detection in a GaAs double quantum dot, we investigate spin relaxation time T_1 and readout visibility of a two-electron singlet-triplet qubit following single-electron dynamic nuclear polarization (DNP). For magnetic fields up to 2 T, the DNP cycle is in all cases found to increase Overhauser field gradients, which in turn decrease T_1 and consequently reduce readout visibility. This effect was previously attributed to a suppression of singlet-triplet dephasing under a similar DNP cycle. A model describing relaxation after singlet-triplet mixing agrees well with experiment. Effects of pulse bandwidth on visibility are also investigated. 
C. Barthel, J. Medford, H. Bluhm, A. Yacoby, C. M. Marcus, M. P.   Hanson, and A. C. Gossard
cond-mat.mes-hall quant-ph