The successful implementation of quantum information strategies will depend on the development of photon emitters and detectors that are capable of producing and resolving a desired number of photons in a particular pulse of light. For added practicality, these devices should operate at ambient temperatures, as opposed to the existing detectors that do the job efficiently but operate at cryogenic temperatures.
Achilles et al. have developed a scheme based on an optic-fiber setup and a couple of standard avalanche photodiodes (APDs). Usually, APDs can distinguish light from no light, but cannot resolve the number of photons in a pulse of light. By splitting the input light pulse into two equal pulses, introducing specified delay times in the paths of two pulses, and then splitting each of those pulses again into two further pulses, the authors effectively create a train of single photons that can be counted by the photodiodes sequentially. By adding up the number of individual incidences at the photodiodes, they show that this simple technique can be used to reconstruct the photon number statistics of weak light pulses with high probability. -- ISO
Opt. Lett. 28, 2387 (2003).
