# Quantum network nodes based on diamond qubits with an efficient nanophotonic interface

## TL;DR

This paper demonstrates a diamond nanocavity with silicon-vacancy centers and nuclear spins as a promising quantum network node, achieving high photon-spin coupling and long coherence times for quantum communication.

## Contribution

It introduces an efficient diamond-based quantum node with integrated SiV centers and nuclear spins, enabling high-fidelity photon interfaces and long-lived quantum memories.

## Key findings

- Achieved high cooperativity (C > 30) in SiV-cavity coupling.
- Demonstrated heralded single-photon storage with coherence times over one millisecond.
- Realized universal control of a two-qubit register with nearly second-long coherence.

## Abstract

Quantum networks require functional nodes consisting of stationary registers with the capability of high-fidelity quantum processing and storage, which efficiently interface with photons propagating in an optical fiber. We report a significant step towards realization of such nodes using a diamond nanocavity with an embedded silicon-vacancy (SiV) color center and a proximal nuclear spin. Specifically, we show that efficient SiV-cavity coupling (with cooperativity $C >30$) provides a nearly-deterministic interface between photons and the electron spin memory, featuring coherence times exceeding one millisecond. Employing coherent microwave control, we demonstrate heralded single photon storage in the long-lived spin memory as well as a universal control over a cavity-coupled two-qubit register consisting of a SiV and a proximal $^{\mathrm{13}}$C nuclear spin with nearly second-long coherence time, laying the groundwork for implementing quantum repeaters.