High fidelity single-shot readout of a transmon qubit using a SLUG   {\mu}wave amplifier
  We report high-fidelity, quantum nondemolition, single-shot readout of a superconducting transmon qubit using a DC-biased superconducting low-inductance undulatory galvanometer(SLUG) amplifier. The SLUG improves the system signal-to-noise ratio by 7 dB in a 20 MHz window compared with a bare HEMT amplifier. An optimal cavity drive pulse is chosen using a genetic search algorithm, leading to a maximum combined readout and preparation fidelity of 91.9% with a measurement time of Tmeas = 200ns. Using post-selection to remove preparation errors caused by heating, we realize a combined preparation and readout fidelity of 94.3%. 
Yanbing Liu, Srikanth Srinivasan, D. Hover, Shaojiang Zhu, R.   McDermott, and A. A. Houck
quant-ph