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

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.

Single-photon frequency conversion via a giant $Λ$-type atom

“…Such structures, which are referred to as "giant atoms", demonstrate striking interference effects that depend on both the atomic size (i.e., the separation between different coupling points) and the photonic frequency [40][41][42][43][44][45][46][47][48][49]. Moreover, non-Markovian retardation effects should also be included if the separations between different coupling points are comparable or even larger than the coherence length of the emitted photons, with which the dynamics can markedly deviate from the Markovian predictions [43,46,[50][51][52]. Recently, giant-atom structures have also been extended to higher dimensions by using optical lattices of cold atoms [53].…”