Experimental measurement of the divergent quantum metric near an Exceptional point

Charly Leblanc

Non-Hermitian systems expand the spectrum of possibilities much beyond that of the Hermitian ones. The quantum geometry of the eigenstates has not been studied extensively in non-Hermitian systems. This geometry is described by the quantum geometric tensor, which includes the Berry curvature and the quantum metric. In Hermitian systems the quantum metric tends to appear as a correction where the Berry curvature is dominant. The situation is different in vicinity of the exceptional points in non-Hermitian systems. Such points arise where the Hermitian and non-Hermitian parts of the Hamiltonian exactly compensate each other. In this work, we measure experimentaly the Stokes vector of the eigenstates and the quantum metric in an organic microcavity with well-defined exceptional points thanks to polarization-dependent strong exciton-photon coupling. The quantum metric diverges in agreement with theoretical predictions for the exceptional points.

Related paper: https://arxiv.org/abs/2011.12037