High-rate Scalable Entanglement Swapping Between Remote Entanglement Sources on Deployed New York City Fibers

TL;DR

This paper demonstrates high-rate, scalable entanglement swapping over deployed NYC fibers using naturally indistinguishable sources, enabling practical quantum networks without complex synchronization.

Contribution

It introduces a scalable entanglement swapping method using natural atomic vapor sources on real-world fiber infrastructure, eliminating the need for shared lasers or pulsed sources.

Findings

Achieved nearly 500 entanglement swaps per second.

Maintained high-quality entanglement over 17.6 km of deployed fibers.

Operated with standard single-photon detectors and synchronization techniques.

Abstract

Entanglement swapping between photon pairs generated at physically separated nodes over telecommunication fiber infrastructure is an essential step towards the quantum internet, enabling applications such as quantum repeaters, blind quantum computing, distributed quantum computing, and distributed quantum sensing. However, successful networked entanglement swapping relies on generating indistinguishable pairs of photons and preserving them over deployed fibers. This has limited most previous demonstrations to laboratory settings or relied on sophisticated methods to maintain the necessary indistinguishability. Here, we demonstrate a scalable entanglement swapping experiment using naturally indistinguishable entanglement sources based on warm atomic vapor cells. Without sharing lasers or optical frequency references between nodes, nor the need for pulsing the sources, we achieve a swapping rate of nearly 500 pairs/s while maintaining the CHSH parameter above 2. Additionally, we demonstrate the scalability of our method by maintaining the quality of the entanglement swapping on 17.6-km of deployed fibers in NYC, relying on commercially available SPADs at the spoke nodes, SNSPDs at the hub and standard time-synchronization techniques. Our work paves the way for the practical deployment of large-scale hub-and-spoke quantum networks within cities and data centers.