Noise in optical quantum memories based on dynamical decoupling of spin states

TL;DR

This paper models noise in optical quantum memories employing dynamical decoupling to extend storage times, showing that with optimized sequences, storage exceeding one second is feasible.

Contribution

It introduces a simple model to quantify noise due to dynamical decoupling in optical quantum memories and evaluates sequences to mitigate this noise.

Findings

Signal-to-noise ratio can be effectively modeled using intrinsic parameters.

Certain dynamical decoupling sequences significantly reduce noise.

Storage times beyond one second are achievable with current technology.

Abstract

Long-lived optical quantum memories are of great importance for scalable distribution of entanglement over remote networks (e.g. quantum repeaters). Long-lived storage generally relies on storing the optical states as spin excitations since these often exhibit long coherence times. To extend the storage time beyond the intrinsic spin dephasing time one can use dynamical decoupling techniques. However, it has been shown that dynamical decoupling introduces noise in optical quantum memories based on ensembles of atoms. In this article a simple model is proposed to calculate the resulting signal-to-noise ratio, based on intrinsic quantum memory parameters such as the optical depth of the ensemble. We also characterize several dynamical decoupling sequences that are efficient in reducing this particular noise. Our calculations indicate that it should be feasible to reach storage times well beyond one second under reasonable experimental conditions.