  The manipulation of the helical edge states of two-dimensional topological
insulators is crucial for the development of technological applications.
Recently, an important step forward, namely, the experimental realization of a
quantum point contact between helical edges, has been accomplished. We
theoretically predict that such a quantum point contact, in the presence of a
time periodic applied electric field, is characterized by a topological quantum
phase transition in the Floquet spectrum. Moreover, we show that it is possible
to detect this dynamical topological quantum phase transition by a bare
conductance measurements.
