Memory-assisted quantum key distribution resilient against multiple-excitation effects

TL;DR

This paper proposes two variants of memory-assisted quantum key distribution using single-photon sources to mitigate multiple excitation effects, demonstrating potential improvements in key rate over traditional schemes with specific ensemble-based memories.

Contribution

It introduces a novel MA-QKD scheme that overcomes multiple excitation issues by employing single-photon sources, showing improved performance with certain atomic ensembles.

Findings

One scheme offers no advantage even with ideal SPSs.

The second scheme can outperform no-memory setups despite imperfections.

Certain atomic ensembles improve rate-versus-distance performance.

Abstract

Memory-assisted quantum key distribution (MA-QKD) has recently been proposed as a technique to improve the rate-versus-distance behavior of QKD systems by using existing, or nearly-achievable, quantum technologies. The promise is that MA-QKD would require less demanding quantum memories than the ones needed for probabilistic quantum repeaters. Nevertheless, early investigations suggest that, in order to beat the conventional no-memory QKD schemes, the quantum memories used in the MA-QKD protocols must have high bandwidth-storage products and short interaction times. Among different types of quantum memories, ensemble-based memories offer some of the required specifications, but they typically suffer from multiple excitation effects. To avoid the latter issue, in this paper, we propose two new variants of MA-QKD both relying on single-photon sources (SPSs) for entangling purposes. One is based on known techniques for entanglement distribution in quantum repeaters. This scheme turns out to offer no advantage even if one uses ideal SPSs. By finding the root cause of the problem, we then propose another setup, which can outperform single no-QM setups even if we allow for some imperfections in our SPSs. For such a scheme, we compare the key rate for different types of ensemble-based memories and show that certain classes of atomic ensembles can improve the rate-versus-distance behavior.