Reducing classical communication costs in multiplexed quantum repeaters using hardware-aware quasi-local policies

Abstract Future quantum networks will have nodes equipped with multiple quantum memories, allowing for multiplexing and entanglement distillation. In this work, we introduce "quasi-local" policies for multiplexed quantum repeater chains. In fully-local policies, nodes make decisions based only on knowledge of their own states. In our quasi-local policies, nodes have increased knowledge of state of the repeater chain, but not necessarily global knowledge. Our policies exploit the observation that for most decisions the nodes have to make, they only need to have information about the connected region of the chain they belong to, and not the entire chain. In this way, we not only obtain improved performance over local policies, but we reduce the classical communication (CC) costs inherent to global-knowledge policies. Our policies also outperform the well-known and widely studied nested purification and doubling swapping policy in practically relevant parameter regimes. Via analytical and numerical results, we also identify the parameter regimes in which distillation makes sense and is useful. We also address the question: "Should we distill before swapping, or vice versa?'' Finally, we propose an experimental implementation of a multiplexing-based repeater chain, and experimentally demonstrate the key element, a high-dimensional biphoton frequency comb, and evaluate its anticipated performance.