Giuseppe Luca Celardo - Università Cattolica di Brescia #
Robustness of collective properties to disorder: the case of Superradiance #
Open quantum systems are at the center of many research fields in condensed matter 
physics. 
We will introduce the non Hermitian Hamiltonian approach to open quantum systems, 
showing that this approach, in its simplest form, can be viewed as an extension of the 
Fermi Golden Rule. 
This approach allows to take into account the effect of the opening beyond the 
perturbation limit,
where novel collective effects can arise.
As an example of quantum collective property we consider here 
single excitation Superradiance. 
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Among the many fascinating aspects of these properties, one important open question 
regards their robustness  to the effects induced by the presence of an environment. 
This robustness might enable to exploit coherent quantum effects to
build quantum devices for information technologies and basic energy science. 
Specifically, we analyze the interplay of Superradiance, induced by the coupling
to a continuum of states, and disorder, induced by the coupling with another 
environment, in one dimensional nanostructures. We consider  static disorder (position 
dependent), which leads to Anderson localization. Superradiance is shown to be robust 
with respect to  disorder. 
Moreover the interplay of different environments is shown to lead to novel cooperative 
regimes, such as the "subradiant hybrid regime".