Dephasing mechanisms of diamond-based nuclear-spin memories for quantum networks

TL;DR

This study investigates dephasing mechanisms in diamond-based nuclear-spin quantum memories within a quantum network node, revealing control infidelities and quasi-static noise as primary factors, and demonstrating significant performance improvements.

Contribution

The paper identifies dominant dephasing sources in nitrogen-vacancy center quantum memories and demonstrates a 19-fold enhancement in memory performance using dynamical decoupling.

Findings

Control infidelities and quasi-static noise are major dephasing contributors.

Memory performance improved 19-fold, not limited by electron reinitialization.

Spin-flip channels involve decay from meta-stable singlet states with an 8:1:1 branching ratio.

Abstract

We probe dephasing mechanisms within a quantum network node consisting of a single nitrogen-vacancy centre electron spin that is hyperfine coupled to surrounding $^{13} \text{C}$ nuclear-spin quantum memories. Previous studies have analysed memory dephasing caused by the stochastic electron-spin reset process, which is a component of optical internode entangling protocols. Here, we find, by using dynamical decoupling techniques and exploiting phase matching conditions in the electron-nuclear dynamics, that control infidelities and quasi-static noise are the major contributors to memory dephasing induced by the entangling sequence. These insights enable us to demonstrate a 19-fold improved memory performance which is still not limited by the electron reinitialization process. We further perform pump-probe studies to investigate the spin-flip channels during the optical electron spin reset. We find that spin-flips occur via decay from the meta-stable singlet states with a branching ratio of 8(1):1:1, in contrast with previous work. These results allow us to formulate straightforward improvements to diamond-based quantum networks and similar architectures.