Heat Transfer in Open Quantum Systems
Citation:
Popovic, Maria, Heat Transfer in Open Quantum Systems, Trinity College Dublin.School of Physics, 2023Download Item:
Abstract:
In most situations of practical interest, quantum systems are not isolated from their surroundings but are interacting with an environment. The importance of such situations has been highlighted, for example, in the fields of quantum optics, interacting many-body systems, quantum computation and, as will be the focus of this thesis, thermodynamics of quantum systems. Scientific interest in the fabrication and control of small devices has fuelled attention to non-equilibrium thermodynamics of open quantum systems, and in particular, to detailed understanding of heat transfer in order to minimize wasteful dissipation.
In Part I of this thesis the theory of open quantum systems is introduced. Coupling with an environment leads to the buildup of correlations and as consequence the dynamics of the open quantum system can no longer be described with a unitary time evolution operator. In many cases of interest the presence of strong coupling between system and environment and the presence of memory effects make the dynamics of the system non-Markovian. A numerically exact method based on the path integral formulation, the time-evolving matrix product operator (TEMPO) algorithm, has recently been developed for retrieving the system reduced density matrix in such cases.
In Part II we use the theory presented in Part I to develop a numerically exact method to compute the full counting statistics of heat transfer in non-Markovian open quantum systems, based on the TEMPO algorithm. This approach is applied to the paradigmatic spin-boson model in order to calculate the mean and fluctuations of the heat transferred to the environment during thermal equilibration. We show that system-reservoir correlations make a significant contribution to the heat statistics at low temperature and present a variational theory that quantitatively explains our numerical results. We also demonstrate a fluctuation-dissipation relation connecting the mean and variance of the heat distribution at high temperature.
Next, we investigate the non-equilibrium thermodynamics of pure decoherence. In a pure decoherence process, the system Hamiltonian is in a constant of motion and there is no direct energy exchange between the system and its surroundings. Nevertheless, we find the presence of nontrivial heat dissipation as a result of decoherence alone. We show that the heat distribution for a pure decoherence process corresponds to a mixture of work distributions of cyclical processes, each conditioned on a state of the open system. Inspired by recent experiments on impurities in ultra-cold gases, we demonstrate our general results by studying the heat generated by the decoherence of a qubit immersed within a degenerate Fermi gas in the lowest band of a species-selective optical lattice.
Finally, we discuss the heat dissipation generated by a single projective measurement performed on the open system during a pure decoherence process.
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European Research Council (ERC)
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https://tcdlocalportal.tcd.ie/pls/EnterApex/f?p=800:71:0::::P71_USERNAME:POPOVICMDescription:
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Author: Popovic, Maria
Advisor:
Eastham, PaulPublisher:
Trinity College Dublin. School of Physics. Discipline of PhysicsType of material:
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