Quantum geometry of non-Hermitian systems

The Berry curvature characterizes one aspect of the geometry of quantum states. It materializes, among other consequences, as an anomalous velocity of wave packets. In non-Hermitian systems, wave packet dynamics is enriched by additional terms that can be expressed as generalizations of the Berry connection to non-orthogonal eigenstates. Here, we contextualize these anomalous non-Hermitian contributions by showing that they directly arise from the geometry of the underlying quantum states as corrections to the distance between left and perturbed right eigenstates. By calculating the electric susceptibility for a single-band wave packet and comparing it with the wave packet's localization, we demonstrate that these terms can, in some circumstances, lead to a violation of fluctuation-dissipation relations in non-Hermitian systems. We discuss experimental signatures in terms of response functions and transport signatures.