  The superconducting nanowire single photon detector (SNSPD) is a leading
technology for quantum information science applications using photons, and they
are finding increasing uses in photon-starved classical imaging applications.
Critical detector characteristics, such as timing resolution (jitter), reset
time and maximum count rate, are heavily influenced by the readout electronics
that sense and amplify the photon detection signal. We describe a readout
circuit for SNSPDs using commercial off-the-shelf amplifiers operating at
cryogenic temperatures. Our design demonstrates a 35 ps timing resolution and a
maximum count rate of over 2x10^7 counts per second while maintaining <3 mW
power consumption per channel, making it suitable for a multichannel readout.
