Robust quantum-network memory using spin qubits in isotopically-purified diamond

The realization of large-scale quantum networks hinges on the capability to reliably store quantum entanglement while generating further links. The nitrogen vacancy centre in diamond is a promising system for this role, hosting both a spin-photon interface for remote entanglement and magnetic coupling to nuclear spin qubits. Recent experiments have shown deterministic delivery of entanglement between two network nodes [1], and high-fidelity control of a 10-qubit system [2]. However, combining these advances is challenging due to always-on electron-nuclear couplings which cause nuclear spin decoherence during remote entanglement generation.

In this work, we utilize isotopic engineering of diamond to improve the performance of a nuclear spin quantum network memory by two orders-of-magnitude over the state of the art. Importantly, we find that memory robustness is now limited by stochastic ionisation of the NV rather than by the direct hyperfine coupling alone, and investigate techniques to overcome this challenge. Our work paves the way for advanced quantum network protocols using spins in diamond.

[1] - P. C. Humphreys, et al., Nature 558, 268-273 (2018)
[2] - C. E. Bradley, et al., Phys. Rev. X 9, 031045 (2019)