• correlations and dissipation
• ergotropy
• NISQ hardware
• quantum thermodynamics
• thermal machines
• three-qubit quantum refrigerator

This thesis presents a unified theoretical and experimental study of thermodynamic processes, focused on a three-qubit quantum refrigerator.
The work develops a protocol that leverages ergotropy, the maximal work extractable via cyclic (unitary) operations, to maximize energy extraction from a cold subsystem while minimizing work input and implementation complexity. Theoretical analysis reveals that cooling is feasible only within a specific temperature regime governed by the ordering of thermal populations relative to energy eigenvalues.
We implement this protocol on IBM’s superconducting quantum processors, tackling challenges in thermal state preparation, circuit synthesis, and noise mitigation through circuit complexity reduction, particularly by minimizing the number of two-qubit entangling gates. Measurements demonstrate a temperature-dependent cooling efficiency that peaks when hot and cold qubit temperatures closely match, validating the protocol’s viability on NISQ hardware.
A critical examination of correlations in multipartite systems shows their dual role: depending on the thermodynamic quantity of interest, they can either support or hinder energy transfer. Yet when correlations become too pronounced, they drive up dissipation and ultimately impair performance.
This work bridges fundamental quantum thermodynamics and near-term quantum computing, delivering optimized unitary designs, real hardware validation, and a nuanced understanding of correlations’ impact on quantum thermal machines.