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Non-Hermitian optics

Loss is usually regarded as a undesirable effect to make many wave propagation phenomena diminish, such as negative refraction. However, the reality is far from this simple picture. A system with loss contrast or balanced gain-loss supports exceptional points in a Hamiltonian picture. It allows phase transition of optical properties. This is expected as a basis for a generation of sensitive optical components to be designed. We are interested in the case of metamaterials where we have magnetic responses as well as electric ones.

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)

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