Cangemi, Loris Maria (2020) Environmental effects on dynamics and topological features of quantum systems. [Tesi di dottorato]

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Theoretical models of quantum systems in the presence of their environment find many applications, ranging from condensed matter physics to quantum information science and quantum thermodynamics. In the field of macroscopic quantum systems, the Caldeira-Leggett model has been employed to study the effects of thermal baths on the coherence properties of superconducting qubits. However, if the quantum system of interest consists of many electrons in a solid, the role of the environment can be played by a quantum field of lattice vibrations, i.e. phonons, modeled by means of noninteracting bosons . In this work, we studied widely known models of quantum systems linearly coupled to their bosonic environment, ranging from simple driven two-level systems, i.e. qubits, to many electrons systems. Our approach has been focused on interesting model parameter ranges where well-established weak-coupling approximations fail in describing the physics involved. Indeed, these regimes are interesting and accessible to experiments. In the case of a driven qubit in contact with its environment, strong coupling effects in system-bath interactions, decoherence and crossover to totally incoherent tunneling dynamics have been studied. In addition, by considering prototypical models of fermionic systems strongly coupled to phonons on a lattice, we studied how topological features can be dramatically modified in the presence of electron-phonon interaction.

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