Phase conjugation of single photons

Phase conjugation (PC) of extremely weak signals using a phase-conjugate mirror based on Mandelstam-Brillouin-enhanced four-wave mixing, coupled with an optical quantum amplifier, is considered. PC of a pulse with energy 4*10/sup -17/ J is achieved. PC conditions for amplified superluminescence noise of the optical quantum amplifier are specified and the limiting parameters are estimated. It is shown experimentally that if the signal-to-noise ratio (S/N) is equal to unity, the energy of an input signal for which phase conjugation is possible corresponds to 30 photons per transverse mode.<
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