We study at the single-photon level the nonreciprocal excitation transfer between emitters coupled with a common waveguide. Non-Markovian retarded effects are taken into account due to the large separation distance between different emitter-waveguide coupling ports. It is shown that the excitation transfer between the emitters of a small-atom dimer can be obviously nonreciprocal by introducing between them a coherent coupling channel with nontrivial coupling phase. We prove that for dimer models the nonreciprocity cannot coexist with the decoherence-free giant-atom structure although the latter markedly lengthens the lifetime of the emitters. In view of this, we further propose a giant-atom trimer which supports both nonreciprocal transfer (directional circulation) of the excitation and greatly lengthened lifetime. Such a trimer model also exhibits incommensurate emitter-waveguide entanglement for different initial states in which case the excitation transfer is, however. reciprocal. We believe that the proposals in this paper are of potential applications in large-scale quantum networks and quantum information processing.

中文翻译：

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具有非马尔可夫延迟效应的单光子不可逆激励转移

我们在单光子级研究与公共波导耦合的发射器之间的不可逆激励转移。由于不同的发射器-波导耦合端口之间的分隔距离较大，因此考虑了非马尔可夫延迟效应。结果表明，通过在小原子二聚体的发射极之间引入具有非平凡耦合相位的相干耦合通道，它们之间的激发转移显然是不可逆的。我们证明，对于二聚体模型，不可逆性不能与无退相干的巨型原子结构共存，尽管后者显着延长了发射体的寿命。有鉴于此，我们进一步提出了一种巨原子三聚体，该三聚体既支持激发的不可逆转移（定向循环），又可以大大延长其寿命。对于不同的初始状态，这种三聚体模型还表现出不相称的发射器-波导纠缠，但是在这种情况下，激发转移是存在的。互惠的。我们认为本文中的建议在大规模量子网络和量子信息处理中具有潜在的应用前景。