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Abstract

In this work, we investigate the nontrivial single-photon scattering properties of giant atoms cou-
pled to waveguides that can be an effective platform for realising nonreciprocal and chiral quantum optics. For the two-level giant-atom setup, we identify the condition for nonreciprocal transmission: the external atomic dissipation is further required other than the breaking of time-reversal symmetry by local coupling phases. Especially, in the non-Markovian regime, unconventional revival peaks periodically appear in the reflection spectrum of such a two-level giant-atom system. To explore more interesting scattering behaviours, we further extend the two-level giant-atom system to ∆-type and
∇-type three-level giant atoms coupled to double waveguides without external atomic dissipation.
We analyse the different physical mechanisms for the nonreciprocal and chiral scattering properties of the ∆-type and ∇-type giant atoms. Our proposed giant-atom structures have potential applications of high-efficient single-photon targeted router and circulator for quantum information precessing.