Abstract
<p>Quantum thermal field effect transistor (qtFET) composed of left-qubit, middle-qutrit, and right-qubit subsystems has been proposed and extensively analysed. In this architecture, the left qubit is coupled to the middle qutrit, which in turn interacts with the right qubit. Each subsystem interacts independently with its respective baths. The middle subsystem serves as a modulator. We have shown that the qtFET exhibits functionality analogous to that of a conventional electronic field effect transistor (eFET). The left, right, and middle subsystems of the qtFET correspond to the drain, source, and gate of an eFET in a common gate configuration, respectively. Our results show that the qtFET can precisely modulate thermal currents, highlighting its potential as a fundamental building block for quantum thermal devices and amplifiers in emerging quantum technologies. This qtFET can be used as a modulator in quantum systems with remarkable precision and can be used as a vital component in amplifiers to develop quantum devices. The integration of Bayesian optimization into the parameter optimization of quantum thermal devices has been demonstrated in this thesis. Bayesian optimization has been performed and used for parameter optimization of qtFET. qtFET has been developed to function as amplifier using optimized parameters in an analogous way to an eFET behaves as amplifier. The transconductance of qtFET has been achieved in order of ten thousands using extended search space range, while performing parameter optimization using Bayesian optimization. The amplification factor is taken as the ratio of gate transconductance and differential conductance. Then the amplification factor is optimized using extended upper bound of search space range of coupling strengths, dissipation rates, and energy levels of subsystem of qtFET which resulted in amplification factor in order of ten millions. This qtFET has been developed to detect variations in temperature at the nanoscale ($10^{-9}$) using optimized parameters. In this work, a heatmap depicting the variation of the thermal current as function of middle bath temperature and interaction strength between middle and right subsystem of qtFET has been verified using first law of thermodynamics. Finally, the negative differential thermal resistance (NDTR) has been found to verify the optimized amplification factor results of qtFET in this work.</p>