Storage of a Single Photon in a Highly Non-Linear Medium Based on Rydberg Atoms

Photons are very good candidates to carry quantum information due to their negligible interactions. However, photon-photon interactions are needed to process photonic quantum information. This is very useful for quantum repeater applications [1], in which the success probability of entanglement swapping can be highly increased if the Bell-state measurement is performed deterministically. In the case of photons, it requires mapping them in a non-linear medium at the single-photon level. This strong non-linearity has been demonstrated by using Rydberg atoms, which are atoms excited to states with a high principal quantum number. However, previous experiments with Rydberg atoms have been implemented with weak coherent input states of light [2, 3]. Hence, the mapping of true single photons to a medium with strong single-photon non-linearity is, so far, an outstanding goal. In this work, we have demonstrated the storage and retrieval of a paired single photon on a highly non-linear medium based on atoms excited to Rydberg levels. More recently, we have also enhanced the non-linearity of our ensemble to the single photon-level, as witnessed by the antibunching of a stored and retrieved incoming coherent field [3]. This will allow the storage of a single photon in a medium with single-photon non-linearity.