High-contrast dispersive readout of a superconducting flux qubit using a   nonlinear resonator
  We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87 %; of the missing 13 %, only 3 % is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement. 
A. Lupascu, E. F. C. Driessen, L. Roschier, C. J. P. M. Harmans, J. E.   Mooij