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  • Open Access

Heralded Entanglement of On-Demand Spin-Wave Solid-State Quantum Memories for Multiplexed Quantum Network Links

Jonathan Hänni1,*, Alberto E. Rodríguez-Moldes1,*, Félicien Appas1,*,‡, Soeren Wengerowsky1, Dario Lago-Rivera1,†, Markus Teller1, Samuele Grandi1, and Hugues de Riedmatten1,2

  • *These authors contributed equally to this work.
  • †Present address: TOPTICA Photonics AG, Lochhamer Schlag 19, 82166 Gräfelfing, Germany.
  • ‡Contact author: felicien.appas@icfo.eu
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Phys. Rev. X 15, 041003 – Published 3 October, 2025

DOI: https://doi.org/10.1103/wvv1-6lg8

Abstract

The ability to distribute heralded entanglement between distant matter nodes is a primitive for the implementation of large-scale quantum networks. Some of the most crucial requirements for future applications include high heralding rates at telecom wavelengths, multiplexed operation, and on-demand retrieval of stored excitations for synchronization of separate quantum links. Despite tremendous progress in various physical systems, the demonstration of telecom-heralded entanglement between quantum nodes featuring both multiplexed operation and on-demand retrieval remains elusive. In this work, we combine narrow band parametric photon-pair sources and solid-state quantum memories based on rare-earth doped crystals to demonstrate telecom-heralded entanglement between spatially separated spin-wave quantum memories with fully adjustable recall time and temporal multiplexing of 15 modes. In a first experiment, the storage in the spin state is conditioned on the entanglement heralding. We take advantage of the control over readout pulse phase to achieve feedforward conditional phase shifts on the stored photons depending on which heralding detector clicked. We exploit this effect to double the entanglement heralding rate for a given quantum state up to 510  counts/s, with an associated detection rate of 0.32  counts/s and measured positive concurrence by up to 6 standard deviations. In a second experiment, we simulate the communication time of a long-distance link by implementing an unconditional storage scheme with a dead time of 100  μs. We take advantage of temporal multiplexing to increase the entanglement rates by a factor of 15 with respect to single mode storage, reaching a value of 22  counts/s per heralding detector. These results establish our architecture as a prime candidate for the implementation of scalable high-rate quantum network links.

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Popular Summary

A major challenge in building quantum networks is how to share quantum entanglement across long distances. Entanglement is a fragile resource that enables powerful applications in computing, sensing, and secure communication, but optical losses make it difficult to maintain over long fiber links. Quantum repeaters have been proposed as a solution. In this study, we report a key step forward: the successful demonstration of heralded entanglement—a confirmation of entanglement via a separate signal—between two spatially separated solid-state quantum memories featuring properties crucial for quantum repeaters.

We achieve this by pairing each quantum memory with a source of photon pairs. One photon is stored locally in the memory while the other—at telecom wavelength—is detected halfway between the two locations. Through the detection of a single telecom photon, the quantum memories are projected into an entangled state. Importantly, the entanglement is read out on demand, a key resource for using the quantum memories as synchronizing devices in quantum networks. We also show that the memories have the property of temporal multimodality, meaning they can store photons arriving at different times within a given window. This feature greatly enhances the overall rate of entanglement distribution, a crucial requirement for scalable quantum repeaters.

While improvements in memory efficiency and storage time are still needed to extend the range of entanglement distribution to larger distances, our current system is already suitable for implementing elementary network segments spanning several kilometers. Looking ahead, this progress lays the groundwork for connecting distant metropolitan areas, bringing us closer to realizing a large-scale quantum internet.

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Phys. Rev. X 15, 041003– Published 3 October, 2025
  • Received 14 February 2025
  • Revised 11 July 2025
  • Accepted 15 August 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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