Online Seminars on Non-Hermitian Physics: #5 Angelo Carollo
Channel: NH Seminar Series
Date: 19/07/2023

Title: Exotic effects and topology in Hermitian and non-Hermitian Waveguide QED

Abstract:
As light can mediate interactions between atoms in a photonic environment, engineering it for endowing the photon-mediated Hamiltonian with desired features is crucial in quantum research. 

In the first part of the talk I will discuss exotic properties of interactions mediated by non-Hermitian reservoirs, made of lossy photonic lattices. I will show in a paradigmatic case study that when these losses are suitably structured, exotic emission properties can be observed. Photons can mediate dissipative, fully non-reciprocal, interactions between the emitters with range critically dependent on the loss rate. 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. 

In the second part of the talk I will introduce general theorems on the topology of photon-mediated interactions in terms of both Hermitian and non-Hermitian topological invariants, unveiling the phenomena of topological preservation and reversal, and revealing a system-bath topological correspondence. Depending on the Hermiticity of the environment and the parity of the spatial dimension, the atomic and photonic topological invariants turn out to be equal or opposite. Consequently, the emergence of atomic and photonic topological boundary modes with opposite group velocity in two-dimensional Hermitian topological systems is established. Owing to its general applicability, these results can guide the design of Hermitian and Non-Hermitian topological systems.

Live on Wednesday 19July 2023 at 15:00 CEST.

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