On the ubiquity of Beutler-Fano profiles: from scattering to dissipative processes

TL;DR

This paper reviews and extends Fano interference models to include dissipative effects from thermal baths, providing solutions for Hamiltonians with discrete-continuous spectra and analyzing their implications for experiments.

Contribution

It offers a unified solution for discrete-continuous Hamiltonians with dissipation, updating classical models to include thermal bath effects and analyzing their impact on Fano lineshapes.

Findings

Fano lineshape persists with parameter rescaling under dissipation.

Dissipation introduces a Lorentzian component, destroying interference.

Theoretical models are limited by the wideband approximation and bath memory effects.

Abstract

Fano models - consisting of a Hamiltonian with discrete-continuous spectrum - are one of the basic toy models in spectroscopy. They have been succesfull in explaining the lineshape of experiments in atomic physics and condensed matter. These models however have largely been out of the scope of dissipative dynamics, with ony a handful of works considering the effect of a thermal bath. Yet in nanostructures and condensed matter systems, dissipation strongly modulates the dynamics. In this article, we present an overview of the theoretical works dealing with Fano interferences coupled to a thermal bath and compare them to the scattering formalism. We provide the solution to any discrete-continuous Hamiltonian structure within the wideband approximation coupled to a Markovian bath. In doing so, we update the toy models that have been available for unitary evolution since the 1960s. We find that the Fano lineshape is preserved as long as we allow a rescaling of the parameters, and an additional Lorentzian contribution that reflects the destruction of the interference by dephasings. We discuss the pertinence of each approach - dissipative and unitary - to different experimental setups: scattering, transport and spectroscopy of dissipative systems. We finish by discussing the current limitations of the theories due to the wideband approximation and the memory effects of the bath.