Sharif Digital Repository

A fundamental question in investigating decoherence and equilibrium of a system in contact with a bath is how its entropy changes in time. Normally, von Neumann’s entropy is used in such studies to quantize degree of decoherence. Recently, certain researches have been conducted addressing entropy rate and various bounds have been achieved for this quantity, utilizing which one can discuss decoherence rate and equilibrium state of open systems.In this thesis, we introduce these bounds and try to improve them. Using improved bound we will show that for almost all conceivable initial states of the system and the bath, average of entropy rate will be negligible. This result is obtained under... 

The relationship between quantum theory and thermodynamics has gained so much attention in recent years. Thermodynamics is indeed a phenomenological science and its theoretical foundations are not clear as well. In the nineteenth century, Boltzmann tried to establish a connection between concepts of thermodynamics and classical mechanics (as a consistent theoretical domain). With development of quantum mechanics in twentieth century, the possibility of analyzing and formulating of the multi-particle systems based on quantum formalism increased. Quantum approach to thermodynamic phenomena has been studied in various ways. Here basic questions are, e.g. how to define Thermodynamic entities... 

The study of thermodynamics of small-scale systems or quantum thermodynamics has been recently receiving a lot of attention from quantum scientists in the field of quantum information. The main purpose of this thesis is to review the effects of quantum phenomena such as correlations, on the laws of thermodynamics and specifically on the efficiency of quantum heat engines. We first review some of the most important topics of classical thermodynamics such as the laws of thermodynamics, thermodynamic potentials and heat engines. The trade-off between power and efficiency for classical heat engines is investigated. It is shown that, this is impossible to have a heat engine performing with the... 

Investigation of the consistency between physical theories has always resulted in the advancement of physics. Meanwhile, study of the consistency between quantum mechanics and thermodynamics has led to the development of a branch in theoretical physics called quantum thermodynamics. In addition to the consistency problem,employing other features of quantum mechanics such as coherency and entanglement, to enhance thermodynamic processes is another ongoing subject of research. In order to study the thermodynamics of quantum systems, we use the first law of thermodynamics to present a derivation of quantum potential. Quantum potential is a term in the equations of motion of a quantum system of... 

Quantum thermodynamics is a new field of study in physics, which by considering the fundamentals of statistical mechanics, open quantum system, quantum information and mesoscopic system aims at the investigation of quantum systems from a thermodynamical point of view. To achieve these aims, a better understanding of the relations between quantum and thermodynamics fundamentals is essential. Energy and correlation are two key concepts in statistical mechanics and quantum thermodynamics (and information), respectively, that studying the relation between them will shed light on the fundamentals of quantum thermodynamics. As generating any correlation in quantum systems with initial heat state... 

Up to this day, no conflict ever observed between experiments and the predictions of quantum mechanics. Scientists are in the belief that quantum mechanics is a universal theory and all the systems, even the classical ones, are quantum mechanical in their nature. In this regard, modeling the Earth-Sun dynamics using Hydrogen atom Hamiltonian has been addressed. Since we understand the classical systems with trajectories, we used Bohmian mechanics as an alternative way to study the Earth-Sun dynamics in a quantum fashion. Moreover, for better understanding the concept of the quantum to classical transition, we studied quantum thermodynamics. Accordingly, we described open quantum systems in... 

For a physical system, equilibrium is defined as a state in which the values of macroscopic quantities describing the system do not change in time. We observe systems around us reaching equilibrium every day. Describing such a seemingly simple phenomena has remained as one of the important challenges in theoretical physics. So far, various explanations for thermalization (approach to equilibrium) have been offered within classical and quantum thermodynamics. In classical statistical mechanics, the microcanonical ensemble provides a suitable prediction of the thermal behavior of a closed system. In this ensemble, using ergodic hypothesis and chaos theory one can assume that all microstates...