RT info:eu-repo/semantics/doctoralThesis
T1 Internal components of continuous quantum thermal machines.
A1 González López, Javier Onam
A2 Programa de Doctorado en Astrofísica
K1 Teoría cuántica
K1 Termodinámica
AB The dynamics of continuous quantum machines weakly coupled to thermalreservoirs is described by master equations when the bath temperatures arehigh enough. If, in addition, the bare frequency gaps are much larger thanthe thermal couplings, the steady state or limit cycle of the device coincideswith the stationary solution of a set of balance equations. This solution canbe analyzed by using Graph Theory. Within this framework, the balanceequations are represented by a graph. We employ a circuit decompositionof this graph to calculate and, most importantly, interpret the stationarythermodynamic properties of different continuous devices. We show that eachcircuit can be associated with a thermodynamically consistent mechanism.This follows from the consistency of the corresponding master equations withthe Laws of Thermodynamics for a proper definition of the energy currents.As a consequence, these circuits can be thought of as internal componentsof the corresponding machine. Thus, the overall steady state functioning ofthe device is the result of the contributions of its internal components andthe interplay between them.We study two types of continuous devices. On one hand, we analyze ab-sorption machines including only thermal baths. We show here that not onlythe total number of constituents circuits affects the device performance, butalso the specific structure of the graph containing these circuits. Crucially,we find that the device connectivity has a major role in the design of optimalabsorption machines. On the other hand, we consider periodically drivendevices with a cyclic pattern of transitions. These machines are connectedto thermal baths and also to a sinusoidal laser field. We study both thestrong and the weak driving limits by using Global and Local master equa-tions respectively. We compare these approaches with the Redfield masterequation. A circuit decomposition can be used to describe the stationarythermodynamic quantities in both limits. Interestingly, given an arbitrarybasis, the device needs coherences to operate in the weak driving limit. How-ever, an incoherent stochastic-thermodynamic model may replicate the samestationary functioning.We conclude that the steady state thermodynamic operation in all themodels under consideration can be described without invoking any quantumfeature. Along these lines, the graph approach may be useful for identify-ing genuinely quantum effects in other continuous machines. For example,devices with non-cyclic pattern of transitions and degenerate states.
YR 2019
FD 2019
LK http://riull.ull.es/xmlui/handle/915/24554
UL http://riull.ull.es/xmlui/handle/915/24554
LA en
DS Repositorio institucional de la Universidad de La Laguna
RD 24-abr-2024