Single-photon nonreciprocal excitation transfer with non-Markovian retarded effects

TL;DR

This paper investigates nonreciprocal single-photon excitation transfer in emitter-waveguide systems, highlighting the effects of non-Markovian retarded dynamics and proposing a giant-atom trimer to achieve both nonreciprocity and enhanced lifetime.

Contribution

It introduces a giant-atom trimer model that supports nonreciprocal transfer and longer emitter lifetimes, addressing limitations of previous dimer models.

Findings

Nonreciprocal transfer achieved with phase-controlled coherent coupling.

Giant-atom dimer cannot have both nonreciprocity and decoherence-free states.

Giant-atom trimer supports directional circulation and longer lifetimes.

Abstract

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.