title: Applications of fidelity measures to complex quantum systems.
abstract: We revisit fidelity as a measure for the stability and the complexity of the quantum motion of single-and many-body systems. Within the context of cold atoms, we present an overview of applications of two fidelities, which we call static and dynamical fidelity, respectively. The static fidelity applies to quantum problems which can be diagonalized since it is defined via the eigenfunctions. In particular, we show that the static fidelity is a highly effective practical detector of avoided crossings characterizing the complexity of the systems and their evolutions. The dynamical fidelity is defined via the time-dependent wave functions. Focusing on the quantum kicked rotor system, we highlight a few practical applications of fidelity measurements in order to better understand the large variety of dynamical regimes of this paradigm of a low-dimensional system with mixed regular-chaotic phase space.
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università di Parma, Via G.P. Usberti 7/a, 43124 Parma, Italy INFN, Sezione di Milano Bicocca, Gruppo Collegato di Parma, Italy Institut für Theoretische Physik, Philosophenweg 12, Universität Heidelberg, 69120 Heidelberg, Germany sandromarcel.wimberger@unipr.it.
authors.forename: Sandro
authors.identifier: http://orcid.org/0000-0002-8433-1733
authors.initials: S
authors.lastname: Wimberger
keywords: Bose–Einstein condensates; avoided crossings; cold atoms; fidelity; many-body theory; quantum chaos