Zero-width resonances and exceptional points in molecular photodissociation

Abstract

In the Hamiltonian describing the interaction of a molecule with a continuous laser field, the wavelength and the intensity of the field are two external parameters which can be varied at will, within realistic limits. Floquet formalism provides complex eigenenergies with an imaginary part giving the photodissociation rate. Two interesting features emerge from this treatment. For some specific laser intensities, the imaginary part can vanish. This means that Zero-Width Resonances can be produced. It is also possible to choose the laser parameters to provoke the coalescence of two resonances (complex eigenenergies and wavefunctions) of the wave equation. Such points in the parameter plane are called exceptional and have been studied in many areas of physics. The existence of Zero-Width Resonances and of Exceptional Points has important consequences which are described in the article. Advantage can be taken of them in laser control strategies dealing with vibrational purification or transfer, with the ultimate goal of molecular cooling. © 2010 Wiley Periodicals, Inc.