ECAMP 15

Non-Hermitian skin effect (NHSE) has now become the paradigmatic example of the topologically nontrivial impact of loss or gain in optical and condensed matter systems. Here, I will present our latest theoretical results on an analog of NHSE in the platform of chiral waveguide quantum electrodynamics — the area of quantum optics studying interaction with propagating photons with atoms in a waveguide [1].

I will focus on the Non-Hermitian Skin effect for the bound states of interacting photons pairs propagating in a waveguide and chirally coupled to an array of atoms [2]. I will demonstrate the concentration of bound modes at the edge of the array that can be interpreted as a non-Hermitian skin effect. The mechanism behind this effect is rather unusual: contrary to the usual local loss or gain, the spectrum for the bound states in the infinite structure is lossless. Instead, the non-Hermiticity for bound pairs is driven by their dissociation into scattering states of photons in the finite structure. Unexpectedly, the bound pairs are concentrated at the left edge of the array when photons are preferentially emitted to the right, and vice versa.

The coexistence of the continuum with the quasiparticle dispersion branch is a generic feature for the energy spectra of various many-body systems, for example, with plasmonic or magnonic excitations. Thus, we believe that our results could apply beyond one-dimensional systems and beyond setups with atom-photon coupling.

[1] A. S. Sheremet, M. I. Petrov, I. V. Iorsh, A. V. Poshakinskiy, and A. N. Poddubny, Waveguide quantum electrodynamics: Collective radiance and photon-photon correlations, Rev. Mod. Phys. 95, 015002 (2023).

[2] J. Shi and A.N. Poddubny, Chiral Dissociation of Bound Photon Pairs for a Non-Hermitian Skin Effect, arXiv:2501.09417