Storage and retrieval of a single photon emitted by a quantum memory on a highly excited Rydberg state

Summary form only given. Strong interaction between two single photons [1], is a long standing and important goal in quantum photonics. This would enable a new regime of nonlinear optics and unlock several applications in quantum information science, including photon-photon gates and deterministic Bell-state measurements for quantum networking. In the context of quantum networks [2], a particularly important case is to achieve strong interaction between single photons from independent photon pairs that can be stored in quantum memories. So far, most of the efforts towards nonlinear effects at the single-photon level have been realized using weak classical input light.In this contribution, we demonstrate the storage and retrieval of a paired single photon emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atomic excitations [3,4]. We demonstrate that non-classical correlations between the two photons persist after the retrieval from the Rydberg ensemble. We show that our Rydberg cold atomic ensemble displays optical nonlinearity with input pulses containing few tens of photons. Our results [5], mark an important step towards deterministic photonphoton interactions, and may enable deterministic Bell-state measurement with multimode quantum memories.