Quantum interference of telecom photons from independent quantum network nodes. Part II – Experimental demonstration

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. As a first demonstration of our platform, we measure the indistinguishability between the telecom photons generated in our platform through a Hong-ou Mandel interference experiment and find a visibility well beyond the classical bound. We further present a clear path towards spin-spin entanglement generation using such photons, setting the stage for the realization of metropolitan scale quantum networks.

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

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