Single-photon detectors are finding increasingly wide application in all branches of science and technology thus a precise knowledge of their quantum efficiency is an essential prerequisite. We have performed the first proof-of-principle demonstration of a means to determine the quantum efficiency by which no second detector or reference standard is required. This absolute self-calibration method is based on the time correlation of entangled photons pairs emitted in spontaneous parametric down conversion. The measured quantum efficiency of a Si avalanche photodiode single-photon detector agrees well with the product specifications.
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