Efficiency and power output of a two-stroke quantum heat engine with a collisional model consisting of N ≤ 5 qubits

Abstract

Heat engines are thermal devices that convert input energy from a thermal reservoir to generate useful work. However, not all energy is converted into mechanical work—some is discarded into a heat sink, such that the measure of the ratio of work output to heat input is called efficiency. The power of a heat engine characterizes the work-output rate. In the quantum regime, quantum heat engines (QHEs) operate the same way but use quantum matter as a working substance. In this paper, the efficiency and power output of a stroboscopic two-stroke QHE with a collisional model are evaluated, where the working substance is a linear chain of N uncoupled qubits. The numerical calculations show that as the interaction strength is increased between qubits, the QHE yields higher efficiency and power output. However, it takes a larger number of cycles for the engine to reach the Otto efficiency as the qubit size is increased. In addition, the QHE yields a stable power output, where the smaller qubit system sizes have higher power outputs.