Pulse Current Measurements and Rabi Oscillations in a dc SQUID Phase Qubit

We have used 2 ns pulses of current to read out the states of a Nb/AlO x /Nb dc SQUID phase qubit at 25 mK. Plotting the number of escape events that occur versus the size of the current pulse reveals a series of steps corresponding to the occupancy of different energy levels. After calibrating the measurement pulses, we fit these steps to determine the population in each level. Rabi oscillations were viewed using this technique. The single-shot measurement fidelity was theoretically analysed and the optimal single pulse in our device was determined.