May 2012
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## Bypassing the bandwidth theorem with PT symmetry

Hamidreza Ramezani, J. Schindler, F. M. Ellis, Uwe Guenther, Tsampikos Kottos

The beat time $${\tau}_{fpt}$$ associated with the energy transfer between two coupled oscillators is dictated by the bandwidth theorem which sets a lower bound $${\tau}_{fpt}\sim 1/{\delta}{\omega}$$. We show, both experimentally and theoretically, that two coupled active LRC electrical oscillators with parity-time (PT) symmetry, bypass the lower bound imposed by the bandwidth theorem, reducing the beat time to zero while retaining a real valued spectrum and fixed eigenfrequency difference $$\delta\omega$$. Our results foster new design strategies which lead to (stable) pseudo-unitary wave evolution, and may allow for ultrafast computation, telecommunication, and signal processing.

http://arxiv.org/abs/1205.1847
Classical Physics (physics.class-ph)

## Experimental observation of the dual behavior of PT-symmetric scattering

Zin Lin, Joseph Schindler, Fred M. Ellis, Tsampikos Kottos

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)