Experimental observation of the dual behavior ofPT-symmetric scattering

We investigate experimentally parity-time (PT) symmetric scattering using $LRC$ circuits in an inductively coupled PT-symmetric pair connected to transmission line leads. In the single-lead case, the PT-symmetric circuit acts as a simple dual device---an amplifier or an absorber depending on the orientation of the lead. When a second lead is attached, the system exhibits unidirectional transparency for some characteristic frequencies. This nonreciprocal behavior is a consequence of generalized (nonunitary) conservation relations satisfied by the scattering matrix.