Limits to non-cryogenic single-photon count rates
In single-photon quantum communications it is often the case that, regardless of the encoding or protocol in use, the performance is strongly limited by the performance of the detectors. With this motivation, there have been significant advances in the most critical parameters of single-photon detector performance: efficiency, noise, and timing resolution. Recently, research has been aimed at improving the maximum usable count rate, particularly in widely available Geiger-mode avalanche photodiodes. In these detectors, the recovery time after an avalanche can be minimized by minimizing the amount of charge required to discriminate an avalanche from noise, the fundamental limit being the noise in the pickup resistor. We present techniques that allow efficient single-photon detection with less than 100 fC per avalanche, and count rates in the 100 MHz regime, and discuss our approach to reach Johnson-noise limited single-photon detection.