Quantum metric and wave packets at exceptional points in non-Hermitian systems

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Topological physics is based on topological invariants such as the Chern number, which is the integral of the Berry curvature. The quantum metric is complementary to the Berry curvature in the quantum geometric tensor, but its role is much less understood. The authors show here that it becomes dominant for the wave-packet dynamics at exceptional points in strongly non-Hermitian systems. The authors demonstrate that, thanks to the divergent metric, such wave packets (e.g., light beams) exhibit nonvanishing velocity with controllable direction.