High fidelity qubit readout with the superconducting low-inductance undulatory galvanometer microwave amplifier
David J. Hover, S. Zhu, Ted Thorbeck, Guilhem J. Ribeill, D. Sank, J. Kelly, R. Barends, John M. Martinis, R. McDermott · Applied Physics Letters · 2014
We describe the high fidelity dispersive measurement of a superconducting qubit using a microwave amplifier based on the Superconducting Low-inductance Undulatory Galvanometer (SLUG). The SLUG preamplifier achieves gain of 19 dB and yields a signal-to-noise ratio improvement of 9 dB over a state-of-the-art HEMT amplifier. We demonstrate a separation fidelity of 99% at 700 ns compared to 59% with the HEMT alone. The SLUG displays a large dynamic range, with an input saturation power corresponding to 700 photons in the readout cavity.