  In closed quantum systems, a dynamical phase transition is identified by
nonanalytic behaviors of the return probability as a function of time. In this
work, we study the nonunitary dynamics following quenches across exceptional
points in a non-Hermitian lattice realized by optical resonators. Dynamical
quantum phase transitions with topological signatures are found when an
isolated exceptional point is crossed during the quench. A topological winding
number defined by a real, noncyclic geometric phase is introduced, whose value
features quantized jumps at critical times of these phase transitions and
remains constant elsewhere, mimicking the plateau transitions in quantum Hall
effects. This work provides a simple framework to study dynamical and
topological responses in non-Hermitian systems.
