In contrast to conventional photon counters that can only detect the absence of photons, Visible Light Photon Counter (VLPC) has the capability to discriminate photon number states. Based on reliable PMT sensitive in the visible spectral range, this photon counting system is able to detect weak optical signals down to the single photon level. It is important in many quantum information processing applications.
Photon counter functions by absorbing photons from the field, converting single photons into electronic information (many thousands of electrons) with high quantum efficiency.