| Microcavities are open quantum systems. They have been successfully described by non-hermitian Hamitonians so far. The degeneracy of the non-hermitian matrix, often called as an exceptional point (EP), has several non-trivial characteristics such as formation of a square root branch-point and coalescence of non-othorgonal eigenvectors. In this talk we present how these characteristics manifest themselves in physics of microcavities, which covers experimental observation of EP in quardrupole-deformed optical microcavities, output directions of spiral cavities, and uni-directional output of coupled non-identical microdisks. Finally we discuss the EP in Hamiltonian systems described by Floquet operators. |
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