Efficient photon number detection with silicon avalanche photodiodes

We demonstrate an efficient photon number detector for visible wavelengths using a fast-gated silicon avalanche photodiode. Using sub-nanosecond voltage gates with a self-differencing circuit, the device is able to resolve up to four photons in an incident optical pulse, with a detection probability of up to 91.1 % at 1 GHz. With this performance and close to room temperature operation, fast-gated silicon avalanche photodiodes are ideal for optical quantum information processing that requires single-shot photon number detection.