Exotic interactions mediated by a non-Hermitian photonic bath

TL;DR

This paper explores how non-Hermitian photonic lattices with structured losses can mediate exotic, non-reciprocal, and tunable photon interactions between quantum emitters, revealing new physics beyond traditional Hermitian systems.

Contribution

It demonstrates that non-Hermitian photonic baths can induce unique, non-reciprocal emitter interactions with controllable range, including a realization of the Hatano-Nelson model at an exceptional point.

Findings

Photons mediate dissipative, non-reciprocal interactions.

Interactions depend critically on loss rate and boundary conditions.

At the exceptional point, interactions become nearest-neighbor and translationally invariant.

Abstract

Photon-mediated interactions between quantum emitters in engineered photonic baths is an emerging area of quantum optics. At the same time, non-Hermitian (NH) physics is currently thriving, spurred by the exciting possibility to access new physics in systems ruled by non-trivial NH Hamiltonians - in particular photonic lattices - which can challenge longstanding tenets such as the Bloch theory of bands. Here, we combine these two fields and study the exotic interaction between emitters mediated by the photonic modes of a lossy photonic lattice described by a NH Hamiltonian. We show in a paradigmatic case study that structured losses in the field can seed exotic emission properties. Photons can mediate dissipative, fully non-reciprocal, interactions between the emitters with range critically dependent on the loss rate. When this loss rate corresponds to a bare-lattice exceptional point, the effective couplings are exactly nearest-neighbour, implementing a dissipative, fully non-reciprocal, Hatano-Nelson model. Counter-intuitively, this occurs irrespective of the lattice boundary conditions. Thus photons can mediate an effective emitters' Hamiltonian which is translationally-invariant despite the fact that the field is not. We interpret these effects in terms of metastable atom-photon dressed states, which can be exactly localized on only two lattice cells or extended across the entire lattice. These findings introduce a new paradigm of light-mediated interactions with unprecedented features such as non-reciprocity, non-trivial dependence on the field boundary conditions and range tunability via a loss rate.