Deterministic photon-atom and photon-photon interactions based on single-photon Raman interaction

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.