Inducing topology via giant atoms: bound states and chiral emission

Abstract:
We study quantum emitters coupled non-locally (“giant atoms”) to engineered photonic lattices, and especially in-gap atom-photon bound states mediating decoherence-free interactions in the Markovian regime [1,2]. We present a theorem ruling occurrence of such bound states protected by chiral symmetry [3]. We use this to predict new classes of symmetry-protected bound states (and ensuing decoherence-free Hamiltonians) unachievable with normal atoms (i.e. local coupling) in both 1D and 2D photonics lattices. The giant atom “sees” an effective non-trivial structure of the lattice despite this actually has trivial structure.
We then consider photonic graphene, where it is known that valleys K and K’ have non-zero, yet opposite, Berry curvatures. We show that one can engineer giant atoms (locally breaking time reversal symmetry), which predominantly couple to one valley only. This entails that, by applying a synthetic electric field E, chiral emission from one emitter will occur along the direction orthogonal to E [4]. Thus, somewhat similarly to the aforementioned bound states, the giant atom in a sense distills out an effective topology.

[1] L. Leonforte, A. Carollo, F. Ciccarello, PRL 126, 063601 (2021)
[2] M. Bello, G. Platero, J. I. Cirac, and A. González-Tudela, Sci. Adv. 5, eaaw0297 (2019)
[3] X. Sun, L. Leonforte, A. Carollo, F. Ciccarello, to appear on arXiv (2023)
[4] M. A. Pinto et al., in preparation (2023)