HIGH-EFFICIENCY SINGLE-PHOTON DETECTORS

Using correlated photon pairs produced via spontaneous parametric down -conversion, we have measured the absolute single-photon detection eff iciencies and time responses of four detectors: two solid-state photom ultipliers (SSPM's) manufactured by Rockwell International Corp., and two custom-modified single-photon counting modules (SSPM's) manufactur ed by EG&G, Canada. The highest observed efficiencies were 70.9+/-1.9% (with an SSPM, at a wavelength of 632 nm) and 76.4+/-2.3% (with an SP CM, at 702 nm). We believe these to be the highest reported single-pho ton detection efficiencies in the visible spectrum; they are important for quantum cryptography and loophole-free tests of Bell's inequaliti es, as well as more prosaic applications such as photon correlation sp ectroscopy and velocimetry. We found that the time profile for coincid ences between the SSPM and the SPCM consisted of a main peak with a 3. 5-ns full width at half maximum (FWHM) preceded by a smaller peak by 1 1 ns. A similar time profile between two SPCM's displayed only one pea k, with a 300-ps FWHM. Afterpulses were detected in the SPCM's at a le vel of less than 10(-4) of the counting rate, with an exponential deca y time constant of 4.5 mus.