** Spectral Singularities, Unidirectional Invisibility, and Dynamical Formulation of One-Dimensional Scattering Theory **

#### Ali Mustafazade

#### Koç Unıversity, Physics Deptartment

**Abstract:** Complex scattering potentials have surprising properties that real scattering potentials lack. Among these are spectral singularities and unidirectional invisibility. In the first part of this talk, I will survey the recent development in the study of physical meaning and applications of spectral singularities. In particular, I show that they provide the basic mathematical framework for all lasing and antilasing systems. In the second part of the talk, I outline a dynamical theory of potential scattering in one-dimension and offer an inverse scattering scheme for the construction of scattering potentials with desirable properties at a prescribed wavelength. This is based on the curious observation that given a possibly complex scattering potential v(x) we can construct a two-level non-stationary and non-Hermitian Hamiltonian H(t) whose S-matrix coincides with the transfer matrix of v(x). We use this approach to develop a complete perturbative description of the phenomenon of unidirectionally invisibility, construct multi-mode unidirectionally invisible potentials with wavelength-dependent direction of invisibility, and show that the application of the adiabatic approximation for H(t) coincides with the semiclassical (WKB) treatment of the scattering problem. A remarkable outcome of the latter result is the identification of the geometric part of the phase of the adiabatically evolving states with the pre-exponential factor of the WKB wave functions. If time permits, we will also outline a recent solution of a local inverse scattering problem that allows for a exact and explicit construction of scattering potentials with given scattering properties at any prescribed wavelength. This construction has direct applications in optical design.

**References:**

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A. Mostafazadeh, Phys. Rev. Lett. 110, 260402 (2013); arXiv: 1303.2501.

A. Mostafazadeh, Ann. Phys. (N.Y.) 341, 77-85 (2014); arXiv:1310.0592.

A. Mostafazadeh, Phys. Rev. A 89, 012709 (2014); arXiv: 1310.0619.

A. Mostafazadeh, J. Phys. A 47, 125301 (2014); arXiv: 1401.4315.

A. Mostafazadeh, Phys. Rev. A 90, 023833 (2014); arXiv: 1407.1760

**Yer :** MSGSÜ Bomonti Binası, Fizik Bölümü

**Tarih :** 16 Ekim 2014 Perşembe, 15:00