Ultra narrowband telecom polarization entanglement source for future long-distance quantum networks
Résumé
Entanglement has evolved from being a spooky interaction towards a key resource of real-life applications such as absolute secure communication. Today, quantum networking devices are commercially available, typically taking advantage of time-bin or polarisation entanglement, the latter one doubtlessly being easier to analyse thanks to interferometer free set-ups. The communication distance of such systems is generally limited to a few hundreds of kilometres due to intrinsic fibre transmission losses and imperfect detectors. It was shown that the communication distance can be greatly increased when combining entangled pairs of photons and quantum memories. But the narrow absorption bandwidth of current quantum memories is in contrary to the widely used broadband entanglement sources based on non linear inter- actions. More precisely, there is a lack of ultra narrowband sources in the telecom C-band, where fibre losses are minimal and high performance guided-wave optics are available. Here we introduce a high quality polarisation entanglement engineering scheme based on a birefringent de- lay line (BDL). This BDL is applied to generate polarization entanglement from a high efficiency ultra narrowband tele- com photon pair source where no polarisation entanglement is available initially.