Single photon interference in 10 km long optical fibre interferometer

Abstract

Single-photon interference fringes with greater than 90% visibility were measured using a 10 km long optical fibre interferometer. The experiment employed a pulsed semiconductor laser source operating at a wavelength of 1.3 μm and a novel single-photon counting scheme using high-speed germanium avalanche photodiodes. Interferometers of this type could form the basis of future quantum cryptography systems.