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arXiv:2509.09464 · Nature

Entanglement-assisted non-local optical interferometry in a quantum network

Pieter-Jan Stas, Y.-C. Wei, Maxim A. Sirotin, Yan Qi Huan, Umut Yazlar, Francisca Abdo Arias, E. Knyazev, Gefen Baranes, Bartholomeus Machielse, Samuele Grandi, Daniel Riedel, Johannes Borregaard, Hongkun Park, Marko Lončar, Aziza Suleymanzade, Mikhail D. Lukin

Published Feb 25, 2026• 7 citations

Abstract

The sensitivity of non-local optical measurements at low light intensities, such as those involved in long-baseline telescope arrays1,2, is limited by fundamental quantum noise and photon losses3. Distributed quantum entanglement has been proposed as a route towards overcoming these limitations and accessing new regimes of non-local optical sensing4–6. Here we demonstrate the use of entangled quantum memories in a quantum network of silicon–vacancy centres in diamond nanocavities7–9 to experimentally perform such non-local phase measurements. Specifically, we combine the generation of event-ready remote quantum entanglement, photon mode erasure that hides the ‘which-path’ information of temporally and spatially separated incoming optical modes and non-local, non-destructive photon heralding enabled by remote entanglement to perform a proof-of-concept entanglement-assisted differential phase measurement of weak incident light between two spatially separate stations. Demonstrating successful operation of the remote phase sensing protocol with a fibre link baseline up to 1.55 km, our results provide an opportunity for a new class of quantum-enhanced optical imaging methods with potential applications ranging from long-baseline interferometry and astronomy to microscopy10,11. Entangled quantum memories are used in a quantum network of silicon–vacancy centres in diamond nanocavities to experimentally perform non-local phase measurements.

DOI: 10.1038/s41586-026-10171-w

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Quantum networks enable applications ranging from quantum secure communication to distributed quantum computing and quantum-enhanced non-local sensing. Silicon-vacancy (SiV) centers in diamond nano-photonic cavities are a strong candidate platform for quantum networking due to their access to multiple qubits, high operation fidelities, and an efficient matter qubit-photon interface. In this thesis, I provide a background overview of both the field of quantum networking in general and the experimental platform of SiVs in diamond nano-photonic cavities. The thesis shows experimental demonstrations of SiVs from the last six years, including the development of the 29SiV as a quantum node with a two-qubit register and the subsequent remote entanglement of two such nodes over a metropolitan fiber. With this two-node network of SiVs, we implement two quantum networking applications. The first application, blind quantum computing, allows a user to remotely run an arbitrary algorithm on a quantum computer by controlling the measurement basis of photons they receive from the quantum computer, while the quantum computer receives no information about the implemented algorithm. We demonstrate a full blind quantum gate set required to implement an arbitrary quantum algorithm with information-theoretic security. The second application is entanglement-assisted remote optical interferometry. This experiment shows how remotely entangled SiVs can assist the phase sensitivity of long-baseline telescope arrays to better observe weak thermal photonic signals. I finally provide some remarks and propose future directions for the SiV as a quantum networking platform

Abstract A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected by fibre optical infrastructure1–3. Here we demonstrate a two-node quantum network composed of multi-qubit registers based on silicon-vacancy (SiV) centres in nanophotonic diamond cavities integrated with a telecommunication fibre network. Remote entanglement is generated by the cavity-enhanced interactions between the electron spin qubits of the SiVs and optical photons. Serial, heralded spin-photon entangling gate operations with time-bin qubits are used for robust entanglement of separated nodes. Long-lived nuclear spin qubits are used to provide second-long entanglement storage and integrated error detection. By integrating efficient bidirectional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1,350 nm), we demonstrate the entanglement of two nuclear spin memories through 40 km spools of low-loss fibre and a 35-km long fibre loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks.

Quantum networks and remote quantum entanglement serve as vital future quantum communication resources with broad applicability. A key direction lies in extending the baseline of optical interferometers to enhance angular resolution in interferometric imaging. Here, by measuring a simulated thermal light field, we report the demonstration of a memory-assisted nonlocal interferometer achieving a fiber-link baseline up to 20 km while simultaneously showing its capability to compensate for a geometric delay equivalent to 1.5 km. This result demonstrates potential for enhancing the angular resolution of interferometric imaging in the optical band with delocalized single-photon entanglement, and paves the way for future application of quantum memories in astronomical observation.

Quantum networks and remote quantum entanglement serve as vital future quantum communication resources with broad applicability. A key direction lies in extending the baseline of optical interferometers to enhance angular resolution in interferometric imaging. Here, by measuring a simulated thermal light field, we report the demonstration of a memory-assisted nonlocal interferometer achieving a fiber-link baseline up to 20 km while simultaneously showing its capability to compensate for a geometric delay equivalent to 1.5 km. This result demonstrates potential for enhancing the angular resolution of interferometric imaging in the optical band with delocalized single-photon entanglement, and paves the way for future application of quantum memories in astronomical observation.

A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected via fiber optical infrastructure. I will talk about our recent work on utilizing silicon vacancy (SiV) centers in nanophotonic diamond cavities integrated with a telecommunication (telecom) metropolitan quantum network. Specifically, remote entanglement generation is generated by the cavity-enhanced interactions, and long-lived auxiliary memory qubits are used to provide second-long entanglement storage with integrated error detection. By interfacing with efficient bi-directional frequency conversion to telecommunication frequencies, we demonstrate entanglement of two nuclear spin memories through a 35 km long fiber deployed in the Boston urban area, an enabling step towards practical quantum repeaters and large-scale quantum network. I will also talk about an in-progress work on exploring blind and distributed quantum computation through this two-node quantum network.