A photon–photon quantum gate based on Rydberg interactions

The interaction between Rydberg states of neutral atoms is strong and long-range, making it appealing to put it to use in the context of quantum technologies. Recently, first applications of this idea have been reported in the fields of quantum computation¹ and quantum simulation^2–4. Furthermore, electromagnetically induced transparency allows one to map these Rydberg interactions to light^5–15. Here we exploit this mapping and the resulting interaction between photons to realize a photon–photon quantum gate^16,17, demonstrating the potential of Rydberg systems as a platform also for quantum communication and quantum networking¹⁸. We measure a controlled-NOT truth table with a fidelity of 70(8)% and an entangling-gate fidelity of 63.7(4.5)%, both post-selected upon detection of a control and a target photon. The level of control reached here is an encouraging step towards exploring novel many-body states of photons or for future applications in quantum communication and quantum networking¹⁸.