High-efficiency photon-number detection for quantum in-formation processing

The visible light photon counter (VLPC) features high quantum efficiency (QE) and low pulse height dispersion. These properties make it ideal for efficient photon-number state detection. The ability to perform efficient photon-number state detection is important in many quantum information processing applications, including recent proposals for performing quantum computation with linear optical elements. In this paper, we investigate the unique capabilities of the VLPC. The efficiency of the detector and cryogenic system is measured at 543 nm wavelengths to be 85 %. A picosecond pulsed laser is then used to excite the detector with pulses having average photon numbers ranging from 3-5. The output of the VLPC is used to discriminate photon numbers in a pulse. The error probability for number state discrimination is an increasing function of the number of photons, due to buildup of multiplication noise. This puts an ultimate limit on the ability of the VLPC to do number state detection. For many applications, it is sufficient to discriminate between I and more than one detected photon. The VLPC can do this with 99% accuracy.