Abstract
Quantum heat engines are subjected to quantum fluctuations related to their discrete energy spectra. Such fluctuations question the reliable operation of thermal machines in the quantum regime. Here, we realize an endoreversible quantum Otto cycle in the large quasi-spin states of Cesium impurities immersed in an ultracold Rubidium bath. Endoreversible machines are internally reversible and irreversible losses only occur via thermal contact. We employ quantum control to regulate the direction of heat transfer that occurs via inelastic spin-exchange collisions. We further use full-counting statistics of individual atoms to monitor quantized heat exchange between engine and bath at the level of single quanta, and additionally evaluate average and variance of the power output. We optimize the performance as well as the stability of the quantum heat engine, achieving high efficiency, large power output and small power output fluctuations.
Highlights
Quantum heat engines are subjected to quantum fluctuations related to their discrete energy spectra
Microscopic motors are exposed to thermal fluctuations and, at low enough temperatures, to additional quantum fluctuations, which are associated with random transitions between discrete energy levels
These thermal machines are based on harmonic oscillators or two-level systems, and the baths mediating heat exchange are simulated by interaction with either laser fields[7–10] or radiofrequency pulses[11,12]
Summary
Quantum heat engines are subjected to quantum fluctuations related to their discrete energy spectra. We characterize the discrete quantum heat transfer at the level of individual quanta using full-counting statistics[18,19] and monitor the population dynamics of the engine from single-atom and time-resolved measurements of the engine’s quasi-spin distribution along the cycle. We employ this system and techniques to evaluate and optimize the performance as well as the stability of the quantum heat engine, achieving high efficiency, large power output and small power output fluctuations
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