Experimental Measurement of the Divergent Quantum Metric of an Exceptional Point

Direct measurement of a non-Hermitian topological invariant in a hybrid light-matter system

“…Combined with advanced methods for potential landscaping ( 32 ) and the possibility to extract a wide range of observables from the cavity PL, our work affirms exciton polaritons as a solid-state platform for exploring robust topological phenomena that do not occur in Hermitian systems. A recent experiment on organic microcavities with highly polarization-dependent (anisotropic) light-matter coupling ( 57 ) has demonstrated a diverging quantum metric at the EP, in stark difference to Hermitian systems ( 31 ) .…”

“…However, the paired EPs remained elusive in the strong coupling regime despite several experiments on exciton polaritons in anisotropic cavities (36)(37)(38)55). Related EPs in momentum space were observed in microcavities with embedded carbon nanotubes (56) and organic microcrystals (57), but strong exciton-photon coupling in these systems only occurs in one polarization. Our results demonstrate that the exciton polaritons can inherit the EPs from birefringent cavity photons.…”

Anomalous dispersion and negative-mass dynamics of exciton polaritons in an atomically thin semiconductor

“…Although the study of non-Hermitian physics in quantum electronic systems remains difficult, significant progress has been achieved in hybrid photonic systems, where photons are strongly coupled to electronic excitations in a solid state to form exciton polaritons, which are part-light part-matter hybrid quasiparticles [6]. Nontrivial topology of the eigenstates [11,12] and mode selectivity [13] in the vicinity of the exceptional points, band engineering [14] and nonlinear localisation [15] in non-Hermitian lattices, emergence of non-Hermitian topology [16] and divergent quantum geometric metric near an exceptional point [17] have been demonstrated in the strong light-matter coupling regime.…”

Electrically tunable Berry curvature and strong light-matter coupling in birefringent perovskite microcavities at room temperature

“…We do not consider non-Hermitian effects which are weak in our system and only relevant to the physics of exceptional points [33,49,50] which is beyond the scope of our study.…”