Realization of Photonic Quantum Repeater using Silicon-Vacancy Centers in Diamond

Quantum networks promise to connect future quantum computers and enable secure communication, but photon loss over long distances prevents the realization of high rate, large-scale networks. One solution is quantum repeaters, where efficient spin-photon interfaces equipped with long-lived quantum memories capable of storing quantum states over repeated entanglement attempts can mitigate the exponential decay of communication rates over distance. In this work, we demonstrate the use of silicon-vacancy (SiV) centers in diamond nanophotonic cavities as a quantum repeater platform, where the SiV electron is a network qubit which provides cavity-enhanced heralded electron-photon gates (EPG). We control a weakly coupled ¹³C via the hyperfine interaction and show its applicability as a memory qubit with coherence times over 150 ms. Utilizing the EPG and a photon-nuclear entangling (PHONE) gate, we independently generate spin-photon entanglement on the electron (F ~ 0.93) and the ¹³C (F ~ 0.90), and show that the ¹³C stays coherent for over 250 repeated electron entanglement attempts.The memory qubit’s robustness enables the system’s operation as a photonic quantum repeater, where we demonstrate an exponential distance scaling enhancement relative to direct transmission and surpass the repeaterless transmission rate with all system losses accounted for. Finally, we demonstrate progress on three-photon protocols using an additional deterministic ²⁹Si nuclear spin, with our three-qubit node acting as a quantum network router generating simultaneous entanglement with three parties and dynamically routing entanglement between any two parties.

This work was supported by the AWS Center for Quantum Networking, the National Science Foundation (Grant No. PHY-2012023), NSF Center for Ultracold Atoms, the NSF Engineering Research Center for Quantum Networks (Grant No. EEC-1941583), CQN (EEC-1941583), and NSF QuSeC-TAQS OMA-2326787