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## PT-symmetry breaking and universal chirality in a PT-symmetric ring

Derek D. Scott, Yogesh N. Joglekar

We investigate the properties of an $$N$$-site tight-binding lattice with periodic boundary condition (PBC) in the presence of a pair of gain and loss impurities $$\pm i\gamma$$, and two tunneling amplitudes $$t_0,t_b$$ that are constant along the two paths that connect them. We show that the parity and time-reversal PT-symmetric phase of the lattice with PBC is robust, insensitive to the distance between the impurities, and that the critical impurity strength for PT-symmetry breaking is given by $$\gamma_{PT}=|t_0-t_b|$$. We study the time-evolution of a typical wave packet, initially localized on a single site, across the PT-symmetric phase boundary. We find that it acquires chirality with increasing $$\gamma$$, and the chirality reaches a universal maximum value at the threshold, $$\gamma=\gamma_{PT}$$, irrespective of the initial location of the wave packet or the lattice parameters. Our results imply that PT-symmetry breaking on a lattice with PBC has consequences that have no counterpart in open chains.

http://arxiv.org/abs/1203.1345
Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)