We present a pulsed four-wave mixing scheme via a Rydberg state to create, store, and retrieve collective Rydberg polaritons. The storage medium consists of a gas of thermal Rb atoms confined in a $220\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-thick cell, which is heated above room temperature. The experimental sequence consists of a pulsed excitation of Rydberg polaritons via the
D1 line, a variable delay or storage time, and a final retrieval pulse via the
D2 line. The lifetime of the Rydberg polaritons is around 1.2 ns, almost entirely limited by the excitation bandwidth and the corresponding motional dephasing of the atoms. The presented scheme combined with a tightly confined atomic ensemble is a good candidate for a deterministic single-photon source, as soon as strong interactions in terms of a Rydberg blockade are added.
We demonstrate a coherent microwave manipulation of a single optical photon based on a single Rydberg excitation in an atomic ensemble. Due to the strong nonlinearities in a Rydberg blockade region, a single photon can be stored in the formation of Rydberg polariton using electromagnetically induced transparency (EIT). The manipulation of the stored single photon is performed by applying a microwave field that resonantly couples the nS 1/2 and nP 3/2 , while the coherent readout is performed by mapping the excitation into a single photon. We achieve a single photon source with g (2) (0) = 0.29 ± 0.08 at 80 S 1/2 without applying microwave fields. By implementing the microwave field during the storage time and retrieval process, we show the Rabi oscillation and modulation of stored photons that can be controlled to retrieve early or late. Rapid modulation frequencies up to 50 MHz can be obtained. Our experimental observations can be well explained via numerical simulations based on an improved superatom model accounting for the dipole-dipole interactions in a Rydberg EIT medium. Our work provides a way to manipulate the stored photons by employing the microwave field, which is significant for developing quantum technologies.
Quantum nonlinear optics by Rydberg polaritons can enable single-photon transistor and switch, single-photon source, and deterministic quantum information processing. A major hindrance in this study is the fast motional decoherence. Here, we devise a scheme to significantly enhance the coherence of Rydberg polariton by letting the atoms {\it remember} their velocities, or, alternatively, by {\it changing} the phase of Rydberg polariton according to its storage time. After the Rydberg polariton is prepared with a Rydberg state
∣r1⟩, i.e., during the storage time, two laser fields induce a transition between
∣r1⟩ and a nearby Rydberg state
∣r2⟩ via a low-lying intermediate state
∣f⟩ which is largely detuned. In particular, we find that either a
2πN protocol, a
π-wait-
π protocol, or a wait-
π protocol, along with an appropriate choice of
∣f⟩ can lead to a phase-coherent Rydberg polariton upon its retrieval. Importantly, the coherent transition between
∣r1⟩ and
∣r2⟩ ensures that the Rydberg polariton can block the Rydberg excitation of nearby atoms as in usual applications of Rydberg polaritons. Numerics show that the theory can nearly completely eliminate the motional dephasing, leaving Rydberg-state decay as the only fundamental channel of decoherence. This sheds light on a broad application of Rydberg-mediated quantum nonlinear optics.