A photonic entanglement filter with Rydberg atoms

Devices capable of deterministically manipulating photonic entanglement are of paramount importance, because photons are ideal messengers for quantum information. However, due to the non-interacting nature of photons, many photonic quantum operations have only been demonstrated using probabilistic linear-optical approaches, leading to an overwhelming resource overhead and poor scalability. Here we report a novel entanglement filter that transmits the desired photonic entangled state and blocks unwanted ones. In contrast to previous probabilistic approaches, our experiment exploits the strong and controllable photon–photon interaction enabled by Rydberg atoms, so the filtering of undesired states succeeds in every experimental trial. Photonic entanglement with near-unity fidelity can be extracted from an input state with an arbitrarily low initial fidelity. The protocol is inherently robust, and succeeds both in the Rydberg blockade regime and in the interaction-induced dissipation regime. Such an entanglement filter opens new routes towards achieving scalable photonic quantum information processing with multiple ensembles of Rydberg atoms. An entanglement filter based on Rydberg atoms is demonstrated. It transmits a desired photonic entangled state and blocks unwanted ones. Near-perfect photonic entanglement can be extracted from a noisy input with arbitrarily low initial fidelity.