title: Visualization of branch points in PT-symmetric waveguides.
abstract: The visualization of an exceptional point in a PT-symmetric directional coupler (DC) is demonstrated. In such a system the exceptional point can be probed by varying only a single parameter. Using the Rayleigh-Schrödinger perturbation theory we prove that the spectrum of a PT-symmetric Hamiltonian is real as long as the radius of convergence has not been reached. We also show how one can use a PT-symmetric directional coupler to measure the radius of convergence for non-PT-symmetric structures. For such systems the physical meaning of the rather mathematical term radius of convergence is exemplified.
authors.affiliation: Shulich Department of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Shachar
authors.initials: S
authors.lastname: Klaiman
authors.forename: Uwe
authors.initials: U
authors.lastname: Günther
authors.forename: Nimrod
authors.initials: N
authors.lastname: Moiseyev