The thermodynamic properties of quantum heat engines are stochastic owing to the presence of thermal and quantum fluctuations. We here experimentally investigate the efficiency and nonequilibrium entropy production statistics of a spin-1/2 quantum Otto cycle in a nuclear magnetic resonance setup. We first study the correlations between work and heat within a cycle by extracting their joint distribution for different driving times. We show that near perfect correlation, corresponding to the tight-coupling condition between work and heat, can be achieved. In this limit, the reconstructed efficiency distribution is peaked at the deterministic thermodynamic efficiency, and fluctuations are strongly suppressed. We further successfully test the second law in the form of a joint fluctuation relation for work and heat in the quantum cycle. Our results characterize the statistical features of a small-scale thermal machine in the quantum domain, and provide means to control them.

中文翻译：

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量子热机的非平衡涨落


由于存在热涨落和量子涨落，量子热机的热力学特性是随机的。我们在这里实验研究了核磁共振装置中自旋 1/2 量子奥托循环的效率和非平衡熵产生统计数据。我们首先通过提取不同驾驶时间的联合分布来研究一个周期内功和热量之间的相关性。我们表明，可以实现近乎完美的相关性，对应于功和热之间的紧密耦合条件。在这个极限中，重建的效率分布在确定性热力学效率处达到峰值，并且波动被强烈抑制。我们进一步成功地以量子循环中功和热的联合涨落关系的形式测试了第二定律。我们的结果表征了量子域中小型热机的统计特征，并提供了控制它们的方法。