New Journal of Physics

High fidelity readout of a transmon qubit using a superconducting low-inductance undulatory galvanometer microwave amplifier

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We report high-fidelity, quantum non-demolition, 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 6.5 dB in a 20 MHz window compared with a bare high electron mobility transistor 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 = 200 ns. Using post-selection to remove preparation errors caused by heating, we realize a combined preparation and readout fidelity of 94.3%.