Room-temperature source of single photons based on a single molecule in a condensed matter host

A controllable single-photon source comprising:

• a) an optical pump source emitting a pulse of pump radiation at a time T0 having a pump photon energy Ep and a pulse duration Tp;
• and
• b) an active medium emitting output radiation having an output photon energy Eout responsive to said pump pulse, the 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, wherein a single one of said molecules is illuminated by said pump pulse, and 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;
• wherein said pulse duration Tp is selected such that Tvib<Tp<T;
• and
• wherein said output radiation is substantially radiation emitted from said single molecule;
• and
• wherein said output radiation is emitted at a time T1 such that T1−T0 is on the order of T;
• and
• wherein a probability P1 of said output radiation consisting of exactly one photon is substantially greater than a probability P2+ of said output radiation consisting of 2 or more photons.

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 semiconductor nanocrystals 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 semiconductor nanocrystals at a time T0 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 of said semiconductor nanocrystal and a vibrational exciton state having a vibrational electron state Ve and a vibrational hole state Vh associated with an electron state E and a hole state H respectively, said semiconductor nanocrystal having a vibrational relaxation time Tvib for transitions from Ve to E and from Vh to H, and having a lifetime T for recombination of E and H, 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 semiconductor nanocrystal, and wherein said output radiation is emitted at a time T1 such that T1−T0 is on the order of T, and wherein a probability P1 of said output radiation consisting of exactly one photon is substantially greater than a probability P2+ of said output radiation consisting of 2 or more photons;
• whereby said controllable single-photon optical signal is provided.

A controllable single-photon source comprising:

• a) an optical pump source emitting a pulse of pump radiation at a time T0 having a pump photon energy Ep and a pulse duration Tp;
• and
• b) an active medium emitting output radiation having an output photon energy Eout responsive to said pump pulse, the active medium comprising:
• i) a transparent condensed phase host;
• and
• ii) one or more semiconductor nanocrystals within or on said host which are chemically distinct from said host and fluorescent responsive to said pump radiation, wherein a single one of said semiconductor nanocrystals is illuminated by said pump pulse, and wherein said pump photon energy Ep corresponds to a transition between a ground state of said single semiconductor nanocrystal and a vibrational exciton state having a vibrational electron state Ve and a vibrational hole state Vh associated with an electron state E and hole state H respectively, said single semiconductor nanocrystal having a vibrational relaxation time Tvib for transitions from Ve to E and from Vh to H, and having a lifetime T for recombination of E and H;
• wherein said pulse duration Tp is selected such that Tvib<Tp<T;
• and
• wherein said output radiation is substantially radiation emitted from said single semiconductor nanocrystal;
• and
• wherein said output radiation is emitted at a time T1 such that T1−T0 is on the order of T;
• and
• wherein a probability P1 of said output radiation consisting of exactly one photon is substantially greater than a probability P2+ of said output radiation consisting of 2 or more photons.