Efficient entanglement distillation without quantum memory

TL;DR

This paper introduces a new, efficient iterative entanglement distillation protocol that does not require quantum memories, demonstrated experimentally to improve entanglement in phase-diffused states, with potential applications in quantum key distribution.

Contribution

The authors develop and experimentally validate the first quantum-memory-free iterative entanglement distillation protocol, enhancing practicality for quantum communication.

Findings

Successfully distills entanglement for up to three iterations

Data matches results of memory-based schemes

Applicable to phase-diffused two-mode-squeezed states

Abstract

Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibers are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distill entanglement for up to three iteration steps. The data are indistinguishable from those an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution.