  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.
