Single Photons

Orel Bechler, Serge Rosenblum, Itay Shomroni +3 more

We demonstrate a passive scheme for deterministic interactions between a single photon and a single atom. Relying on single-photon Raman interaction (SPRINT), this control-fields free scheme swaps a flying qubit, encoded in the two possible input modes of a photon, with a stationary qubit, encoded in the two ground states of the atom, and can be also harnessed to perform universal quantum gates. Using SPRINT we experimentally demonstrated all-optical switching of single photons by single photons, and deterministic extraction of a single photon from an optical pulse. Applicable to any atom-like Lambda system, SPRINT provides a versatile building block for scalable quantum networks based on completely passive nodes interconnected and activated solely by single photons.

Graham P. Collins

Alan L. Migdall, David A. Branning, Stefania Castelletto

As typically implemented, single-photon sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single-photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand.

Lene Vestergaard Hau

Ray LaPierre

Gavriil Shchedrin

The formulation of the wave function of a single photon has always been in a con ict with the spatial localization of a photon. Lack of the correct treatment for the probability and current density of a single photon resisted self-consistent treatment of the wave function of a single photon. Here we proceed with the construction of the wave function for a single photon that allows us to introduce probability and current density of a single photon. The wave function of a single photon is constructed from the matrix elements of the electric and magnetic elds that couple vacuum state with the Fock state occupied by a single photon. Further we show that the spin of a photon, being projected on the direction of the photon ight propagation, de nes the time evolution of the photon wave function. As the result it can be identi ed with the Hamiltonian of a single photon that establishes Schrodinger equation for a single photon. The Schrodinger description naturally leads to the current and the probability density for a single photon that satis es the continuity equation. The Schrodinger formulation of the Maxwell equations provides a clear physical meaning for the spin of a photon in a similar way to the Dirac equation provides a natural explanation for the spin of an electron.