  Topology in quench dynamics gives rise to intriguing dynamic topological
phenomena, which are intimately connected to the topology of static
Hamiltonians yet challenging to probe experimentally. Here we experimentally
detect momentum-time skyrmions in parity-time (PT)-symmetric non-unitary quench
dynamics, which are protected by dynamic Chern numbers defined for the emergent
momentum-time manifold. Specifically, we experimentally simulate non-unitary
quench dynamics of PT-symmetric topological systems using single-photon
discrete-time quantum walks, and demonstrate emergence of skyrmions by
constructing the time-dependent non-Hermitian density matrix via direct
measurements in position space. Our work experimentally reveals the interplay
of PT symmetry and quench dynamics in inducing emergent topological structures,
and highlights the application of discrete-time quantum walks for the study of
dynamic topological phenomena.
