Regensburg 2022 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 9: Focus Session: Exceptional Points and Non-Hermitian Physics in Semiconductor Systems

HL 9.3: Hauptvortrag

Montag, 5. September 2022, 16:15–16:45, H33

Non-Hermitian effects in exciton polaritons — •Eliezer Estrecho — ARC Centre of Excellence in Future Low-Energy Electronics Technologies and Department of Quantum Science and Technology, Research School of Physics, The Australian National University, Canberra, ACT 2601, Australia

I will present our experimental results highlighting non-Hermitian effects in exciton-polariton systems---quasiparticles arising from the strong coupling of excitons in semiconductors and photons in a cavity. This hybrid system is naturally non-Hermitian due to inherent loss and gain. The former arises from photon leakage through the cavity mirrors and the short lifetime of excitons, while the latter arises from an external pump used to maintain the density, for example, in the creation of Bose-Einstein condensates.

Using exciton-polariton condensates, we demonstrate exceptional points in the deformation parameter space of a quantum billiard. In particular, we are able to trace the energy levels close to the exceptional point, observe the topological Berry phase, and demonstrate the chirality of the state.

We also observe exceptional points in momentum space. By studying the energy and pseudospin structure, we directly measured a novel non-Hermitian topological invariant and differentiated it from its Hermitian counterparts. Furthermore, we also observe an anomalous dispersion resulting from the dissipative coupling of excitons and photons. The resulting inverted dispersion leads to a negative-mass propagation where the particles move in the opposite direction to their momentum.