High-Fidelity Qubit Measurement using a Superconducting Low-Inductance Undulatory Galvanometer Microwave Amplifier

We describe a high-fidelity dispersive measurement of a superconducting Xmon qubit using a microwave amplifier based on the Superconducting Low-inductance Undulatory Galvanometer (SLUG). We will show a qubit measurement fidelity of 99{\%} in 700 ns with the SLUG, compared to 60{\%} without the SLUG. The SLUG amplifier has a gain of 19 dB at 6.6 GHZ. It also improves the signal-to-noise ratio by 9 dB, compared the same circuit without the SLUG. Also, the SLUG amplifier has a large dynamic range, with an input saturation power corresponding to around 600 photons in the readout cavity. All of these properties make the SLUG a promising microwave amplifier for more complex quantum circuits.