Observation of Asymmetric Transport in Structures with Active Nonlinearities

A mechanism for asymmetric transport based on the interplay between the fundamental symmetries of parity (P) and time (T ) with nonlinearity is presented. We experimentally demonstrate and theoretically analyze the phenomenon using, as a reference system, a pair of coupled van der Pol oscillators, one with anharmonic gain and the other with the complementary time reversed anharmonic loss, connected to two transmission lines. An increase of the degree of the gain/loss strength or of the number of PT -symmetric nonlinear dimers in a chain, increases the non-reciprocality effect.