Automated Distribution of Polarization-Entangled Photons Using Deployed New York City Fibers

The distribution of high-fidelity high-rate entanglement over telecommunication infrastructure is one of the main paths toward large-scale quantum networks, enabling applications such as quantum encryption and network protection, blind quantum computing, distributed quantum computing, and distributed quantum sensing. However, the fragile nature of entangled photons operating in real-world fiber infrastructure has historically limited continuous operation of such networks. Here, we present a fully automated system capable of distributing polarization-entangled photons over a 34-km deployed fiber in New York City, achieving high rates of nearly <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mn>5</a:mn><a:mo>×</a:mo><a:msup><a:mn>10</a:mn><a:mn>5</a:mn></a:msup></a:math> pairs/s. Separately, we demonstrate a high fidelity of approximately <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mn>99</d:mn><d:mi mathvariant="normal">%</d:mi></d:math> for rates up to <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><h:mn>2</h:mn><h:mo>×</h:mo><h:msup><h:mn>10</h:mn><h:mn>4</h:mn></h:msup></h:math> pairs/s. Lastly, we achieve 15 days of continuous distribution, with a network up-time of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><k:mn>99.84</k:mn><k:mi mathvariant="normal">%</k:mi></k:math>. Our work paves the way for practical deployment of always-on entanglement-based networks with rates and fidelity adequate for many current and future use cases. Published by the American Physical Society 2024