We consider a quantum relay that is used by two parties to perform several continuous-variable protocols of quantum communication, from entanglement distribution (swapping and distillation) to quantum teleportation, and quantum key distribution. The theory of these protocols is suitably extended to a non-Markovian model of decoherence characterized by correlated Gaussian noise in the bosonic environment. In the worst-case scenario where bipartite entanglement is completely lost at the relay, we show that the various protocols can be reactivated by the assistance of classical (separable) correlations in the environment. In fact, above a critical amount, these correlations are able to guarantee the distribution of a weaker form of entanglement (quadripartite), which can be localized by the relay into a stronger form (bipartite) that is exploitable by the parties. Our findings are confirmed by a proof-of-principle experiment where we show, for the first time, that memory effects in the environment can drastically enhance the performance of a quantum relay, well beyond the single-repeater bound for quantum and private communications.

我们考虑一个量子中继器，该量子中继器可被两方用来执行几个量子通信的连续变量协议，从纠缠分布（交换和蒸馏）到量子隐形传态以及量子密钥分布。这些协议的理论被适当地扩展到以相干的高斯噪声为特征的非马尔可夫退相干模型。在最坏的情况下，继电器发生二分纠缠完全消失的情况，我们证明可以借助环境中经典（可分离）关联的帮助来重新激活各种协议。实际上，超过临界值时，这些相关关系能够保证弱纠缠形式（四方体）的分布，中继器可以将其本地化为各方可以利用的更强形式（两方）。我们的发现得到了一项原理证明实验的证实，该实验首次证明了环境中的记忆效应可以极大地增强量子中继的性能，远远超出了量子通信和专用通信的单中继器范围。