Patent ID: 7068698

Claim:
A method for emitting, at a controllable time, a single-photon optical signal, the method comprising: a) providing an optical pump source emitting pump radiation having a pump photon energy Ep; b) providing an active medium comprising: i) a transparent condensed phase host; and ii) one or more molecules within or on said host which are chemically distinct from said host and fluorescent responsive to said pump radiation; c) illuminating a single one of said molecules at a time T 0 with a pulse of radiation from said pump source having a pulse duration Tp, wherein said pump photon energy Ep corresponds to a transition between a ground state G of said single molecule and a vibrational state V associated with an excited electronic state E of said single molecule, said single molecule having a vibrational relaxation time Tvib for a transition from V to E and having a lifetime T for a transition from E to a state having lower energy, and wherein said pulse duration Tp is selected such that Tvib<Tp<T; and d) emitting output radiation having an output photon energy Eout from said active medium responsive to said pump pulse, wherein said output radiation is substantially radiation emitted from said single molecule, and wherein said output radiation is emitted at a time T 1 such that T 1 −T 0 is on the order of T, and wherein a probability P 1 of said output radiation consisting of exactly one photon is substantially greater than a probability P 2 + of said output radiation consisting of 2 or more photons; whereby said controllable single-photon optical signal is provided.