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.
We report the demonstration of strong coupling between single Cesium atoms and a high-Q chip-based microresonator.
Our toroidal microresonators are compact, Si chip-based whispering gallery mode resonators that confine light to small
volumes with extremely low losses, and are manufactured in large numbers by standard lithographic techniques.
Combined with the capability to couple efficiently light to and from these microresonators by a tapered optical fiber,
toroidal microresonators offer a promising avenue towards scalable quantum networks. Experimentally, laser cooled Cs
atoms are dropped onto a toroidal microresonator while a probe beam is critically coupled to the cavity mode. When an
atom interacts with the cavity, it modifies the resonance spectrum of the cavity, leading to rejection of some of the probe
light from the cavity, and thus to an increase in the output power. By observing such transit events while systematically
detuning the cavity from the atomic resonance, we determine the maximal accessible single-photon Rabi frequency of
Ω0/2π ≈ (100 ± 24) MHz. This value puts our system in the regime of strong coupling, being significantly larger than the dissipation rates in our system.