Harnessing quantum physics has promised powerful and advanced technologies, such as guaranteed secure communications and computational processing beyond that of any classical computer. Photons – single quanta of light – present a promising platform to realise these quantum technologies. Common to many quantum photonics platforms, the non-deterministic nature of generating, manipulating and measuring photons In imperfect systems results in the ‘scaling catastrophe’ severely limiting the size of any composite system.
We address this scaling issue by developing a broadband, room-temperature, inexpensive and indistinguishable source of single photons. We do this by means of a quantum memory in warm rubidium vapour that is capable of efficiently storing GHz bandwidth inputs and recalling them without any additional noise. This device allows for the synchronisation of photon sources based on parametric down-conversion and is in principle capable of delivering high-purity single photons without the need for expensive cryogenics as is required for single emitters in the solid-state.
This work builds on of our previous efforts in Caesium, where we observed a 16% efficiency GHz-bandwidth quantum memory, that added zero noise to the output, evidenced by the retention of the quantum properties of stored and recall single photons with no detectable change in the 98% purity of the input state. We developed simulation tools for the Rubidium system in order to identify the optimal operational parameters, including the optical density and control pulse energy. We find that the quantum memory is capable of performing at an efficiency exceeding 81%. Combining this with high heralding efficiency of a parametric down-conversion source and low loss end-to-end transmission, a nearly deterministic source is within reach, with the next steps to interface the memory with the single-photon source.
