High-efficiency single-photon detectors

Using correlated photon pairs produced via spontaneous parametric down-conversion, we have measured the absolute single-photon detection efficiencies and time responses of four detectors: two solid-state photomultipliers (SSPM’s) manufactured by Rockwell International Corp., and two custom-modified single-photon counting modules (SSPM’s) manufactured 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 SPCM, at 702 nm). We believe these to be the highest reported single-photon detection efficiencies in the visible spectrum; they are important for quantum cryptography and loophole-free tests of Bell’s inequalities, as well as more prosaic applications such as photon correlation spectroscopy and velocimetry. We found that the time profile for coincidences 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 11 ns. A similar time profile between two SPCM’s displayed only one peak, with a 300-ps FWHM. Afterpulses were detected in the SPCM’s at a level of less than ${10}^{\mathrm{-}4}$ of the counting rate, with an exponential decay time constant of 4.5 μs.