A key challenge towards future quantum internet technology is connecting quantum processors at metropolitan scale. Here, we report on heralded entanglement between two independently operated quantum network nodes separated by 10km. The two nodes hosting diamond spin qubits are linked with a midpoint station via 25km of deployed optical fiber. We minimize the effects of fiber photon loss by quantum frequency conversion of the qubit-native photons to the telecom L-band and by embedding the link in an extensible phase-stabilized architecture enabling the use of the loss-resilient single-photon entangling protocol. By capitalizing on the full heralding capabilities of the network link in combination with real-time feedback logic on the long-lived qubits, we demonstrate the delivery of a predefined entangled state on the nodes irrespective of the heralding detection pattern. Addressing key scaling challenges and being compatible with different qubit systems, our architecture establishes a generic platform for exploring metropolitan-scale quantum networks.
@article{arxiv.2404.03723,
title = {Metropolitan-scale heralded entanglement of solid-state qubits},
author = {Arian J. Stolk and Kian L. van der Enden and Marie-Christine Slater and Ingmar te Raa-Derckx and Pieter Botma and Joris van Rantwijk and Benjamin Biemond and Ronald A. J. Hagen and Rodolf W. Herfst and Wouter D. Koek and Arjan J. H. Meskers and René Vollmer and Erwin J. van Zwet and Matthew Markham and Andrew M. Edmonds and Jan Fabian Geus and Florian Elsen and Bernd Jungbluth and Constantin Haefner and Christoph Tresp and Jürgen Stuhler and Stephan Ritter and Ronald Hanson},
journal= {arXiv preprint arXiv:2404.03723},
year = {2024}
}