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Title: Equilibration and thermal machines in quantum mechanics
Author: Malabarba, Artur S. L.
ISNI:       0000 0004 5918 2988
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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This dissertation is about two aspects of quantum thermodynamics, quantum equilibration and thermal machines. First, we investigate equilibration of quantum systems with regards to typical measurements. Considering any Hamiltonian, any initial state, and measurements with a small number of outcomes compared to the dimension, we show that most measurements are already equilibrated. When the initial state is an eigenstate of the observable, most observables are initially out of equilibrium yet equilibrate more rapidly than would be physically reasonable. In search for more physical equilibration times, we turn to two practical scenario: a quantum particle in a one-dimensional box, as observed by a coarse grained position measurement; and a subsystem interacting with a highly mixed environment. We show that equilibration in both of these contexts indeed takes place and does so in very reasonable time scales. Back to a more general context, we present a theory independent definition of equilibration, and show that equilibration of pure states is objectively easier for quantum systems than for classical systems. This shows that quantum equilibration is a fundamental aspect of physical systems, while classical equilibration relies on experimental ignorance. In the subject of thermal machines, we show that a quantum system (the clock) can be used to exactly implement any energy-conserving unitary operation on an engine. When the engine includes a quantum work storage device we can approximately perform completely general unitaries. This can be used to carry out arbitrary transformations of a system without external control. We then show that autonomous thermal machines suffer no intrinsic thermodynamic cost compared to externally controlled ones. Finally, we further improve this construction by showing that the results still hold if the clock and the work storage device are given a more physical Hamiltonian.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available