**Unidirectional zero reflection as gauged Parity-time symmetry**

PT-symmetry can be gauged by a Unitary transformation. It corresponds to a familary of equivalent PT-symmetric systems from a given seed system with conventional PT-symmetry.

New J. Phys. 19, 123041 (2017)

A particular gauge can be taken so that eps(x) = mu(-x)* is regarded as PT-symmetric.

Phys. Rev. A 91, 033825 (2015)

Laser-absorber can be designed by detailed matching of permittivity and permeability.

New J. Phys. 18, 085004 (2016)

**PT-phase transition**

Hamiltonian of a pair of bright and dark atom in the intermediate coupling regime is found to have an effective PT-symmetric Hamiltonian. Phase transition of coherent perfect absorption is observed.

Theory: Phys. Rev. A 87, 053824 (2013)

Experiment: Phys. Rev. Lett. 112, 143903 (2014)