Seminarium Optyczne

In quantum mechanics, the assumed hermicity of the Hamiltonian ensures that the probability of finding aparticle is constant over time. The description of dissipation or gain in a system typically requiresintroduction of non-Hermitian terms. The resulting non-Hermitian Hamiltonian can exhibit propertiesunavailable for typical Hermitian systems. The most striking example of such behavior is the existence ofso-called Exceptional Points (EP), points in parameter space where both eigenvalues and eigenvectorscoalesce (are degenerate).In this work, we introduce the basics of non-Hermitian physics with special emphasis on the properties ofEPs. Specifically, we consider a planar optical microcavity filled with a birefringent liquid crystal. We showhow polarization dependent losses in such a system lead to emergence of EPs. We demonstrate, boththeoretically and experimentally, how owing to the sensibility of the liquid crystal to an external electricfield, it is possible to change the position of the EPs. In particular, we show how EPs can be removed(annihilated) from the system when two of them are brought into a single position