Observation of dynamical vortices after quenches in a system with topology

Topological phases constitute an exotic form of matter characterized by non-local properties rather than local order parameters1. The paradigmatic Haldane model on a hexagonal lattice features such topological phases distinguished by an integer topological invariant known as the first Chern number(2). Recently, the identification of non-equilibrium signatures of topology in the dynamics of such systems has attracted particular attention(3-6). Here, we experimentally study the dynamical evolution of the wavefunction using time-and momentum-resolved full state tomography for spin-polarized fermionic atoms in driven optical lattices(7). We observe the appearance, movement and annihilation of dynamical vortices in momentum space after sudden quenches close to the topological phase transition. These dynamical vortices can be interpreted as dynamical Fisher zeros of the Loschmidt amplitude(8), which signal a so-called dynamical phase transition(9,10). Our results pave the way to a deeper understanding of the connection between topological phases and non-equilibrium dynamics.