Quantum Heat Engines; Multiple-State 1d Box System

Abstract

This thesis examined a quantum Otto engine with a harmonic working medium consisting of two particles to explore the use of wave function symmetry as an accessible resource. It is shown that the bosonic system displays enhanced performance when compared to two independent single particle engines, while the fermionic system displays reduced performance. This explored the trade-off between efficiency and power output and the parameter regimes under which the system functions as engine, refrigerator, or heater. Remarkably, the bosonic system operates under a wider parameter space both when operating as an engine and as a refrigerator. A quantum Otto engine with two particles in harmonic oscillator as its working substance is studied for a quasistatic operation at both high and low temperatures limit. The power and efficiency of the heat engine are derived analytically as functions of the oscillator's frequencies. Using the optimization methods suggested by A.C Hernandez et. al, the heat engine is effectively optimized and found to yield better working conditions in some ranges of frequency and temperature ratios. In the high temperature limit, the figure of merit, a quantity defined as a product of scaled power and scaled efficiency, ψ, was found to be greater than unity in range. Under the same temperature limit, ψ was found to be less than one in the range. Similarly, in the low temperature limit, the figure of merit, ψ , was found to be greater than unity in range. Under the same temperature limit, ψ was found to be less than one in the range. It means that in some ranges of the ratios, it is found to work better in the optimized condition whereas in other ranges it better performs under maximum power working condition. So, it is possible to switch the engine between the two scenarios.