Quantum interference of telecom photons from independent quantum network nodes: Part I - Enabling technologies

Large scale networks where entanglement is generated and exploited between nodes are of great interest for both practical quantum communication applications as well as fundamental tests of nature[1]. The Nitrogen Vacancy (NV) centre in diamond provides currently one of the most advanced nodes, with a recent demonstration of a three-node network [2] showing genuine multi-partite entanglement and entanglement swapping. In order to extend such a network to metropolitan distances, the challenges of broad spectral tuning of emitters and fibre losses need to be addressed. Furthermore, high technical demands for building and controlling distant and independent nodes need to be solved. Here we demonstrate an NV-based platform that overcomes these challenges by employing quantum frequency conversion modules.

Here we show details of the enabling technology that allows for the creation of indistinguishable photons. With a frequency locking scheme we are able to remove any spectral offset between single photons from two separate sources and convert to a single target frequency in the telecom L-band. Furthermore, we will address several of the technical demands of entanglement generation over large distances.

[1] S. Wehner et al, Science 362, (2018)

[2] M. Pompili et al, Science 372, (2021)