We investigate experimentally parity-time \({\cal PT}\) symmetric scattering using \(LRC\) circuits in an inductively coupled \({\cal PT}\)- symmetric pair connected to transmission line leads. In the single-lead case, the \({\cal PT}\)-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 non-reciprocal behavior is a consequence of generalized (non-unitary) conservation relations satisfied by the scattering matrix.

http://arxiv.org/abs/1205.2176
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Mutually coupled modes of a pair of active LRC circuits, one with amplification and another with an equivalent amount of attenuation, provide an experimental realization of a wide class of systems where gain/loss mechanisms break the Hermiticity while preserving parity-time PT symmetry. For a value PT of the gain/loss strength parameter the eigen-frequencies undergo a spontaneous phase transition from real to complex values, while the normal modes coalesce acquiring a definite chirality. The consequences of the phase-transition in the spatiotemporal energy evolution are also presented.

http://arxiv.org/abs/1109.2913
Other Condensed Matter (cond-mat.other); Quantum Physics (quant-ph)