Experimental classification of quenched quantum walks by dynamical Chern number

Topology has rapidly become one of the central topics in modern physics because of its ability to explain various interesting phenomena, especially in condensed matter physics. Topological invariants, serving as indicators for different topological phases, have been widely studied in various quantum systems. Generally, topological invariants are defined in (quasi)equilibrium systems through their ground-state manifold and are used to classify different topological phases. Recently, topological invariants in quantum systems far from equilibrium have been taken into account theoretically in quite different ways. Here, the dynamical Chern number, originally introduced in quenches of static systems, is extended to the quenches of periodically driven systems. Moreover, experimental measurements of dynamical topological invariants appearing in different quantum quenches are reported. The results show that the dynamical Chern number offers an intrinsic way to classify quenched quantum walks, and they demonstrate further its relation to quasiequilibrium topological bulk invariants associated with quenched quantum walks between different topological phases. The classifications by the dynamical Chern number are also compared with the classifications by the behavior of the dynamical topological order parameter. The platform used in this study provides an ideal way to investigate the topology in nonequilibrium quantum systems.