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Work and Fluctuations: Coherent vs. Incoherent Ergotropy Extraction
Quantum ( IF 6.4 ) Pub Date : 2022-07-14 , DOI: 10.22331/q-2022-07-14-762
Marcin Łobejko

We consider a quasi-probability distribution of work for an isolated quantum system coupled to the energy-storage device given by the ideal weight. Specifically, we analyze a trade-off between changes in average energy and changes in weight's variance, where work is extracted from the coherent and incoherent ergotropy of the system. Primarily, we reveal that the extraction of positive coherent ergotropy can be accompanied by the reduction of work fluctuations (quantified by a variance loss) by utilizing the non-classical states of a work reservoir. On the other hand, we derive a fluctuation-decoherence relation for a quantum weight, defining a lower bound of its energy dispersion via a dumping function of the coherent contribution to the system's ergotropy. Specifically, it reveals that unlocking ergotropy from coherences results in high fluctuations, which diverge when the total coherent energy is unlocked. The proposed autonomous protocol of work extraction shows a significant difference between extracting coherent and incoherent ergotropy: The former can decrease the variance, but its absolute value diverges if more and more energy is extracted, whereas for the latter, the gain is always non-negative, but a total (incoherent) ergotropy can be extracted with finite work fluctuations. Furthermore, we present the framework in terms of the introduced quasi-probability distribution, which has a physical interpretation of its cumulants, is free from the invasive nature of measurements, and reduces to the two-point measurement scheme (TPM) for incoherent states. Finally, we analytically solve the work-variance trade-off for a qubit, explicitly revealing all the above quantum and classical regimes.

中文翻译:

工作和波动:相干与不相干的 Ergotropy 提取

我们考虑了一个孤立的量子系统的准概率工作分布,该系统耦合到由理想重量给出的能量存储设备。具体来说,我们分析了平均能量变化和重量方差变化之间的权衡,其中功是从系统的相干和不相干的ergotropy 中提取的。首先,我们揭示了通过利用工作储层的非经典状态,正相干能性的提取可以伴随工作波动的减少(由方差损失量化)。另一方面,我们推导出量子权重的涨落-退相干关系,通过对系统的热熵贡献的相干贡献的倾倒函数定义其能量色散的下限。具体来说,它揭示了从相干中解开 ergotropy 会导致高波动,当总相干能量被解开时,波动会发散。所提出的自主功提取协议显示了提取相干和非相干 ergotropy 之间的显着差异:前者可以减小方差,但如果提取的能量越来越多,其绝对值会发散,而对于后者,增益总是非负的,但可以通过有限的功波动提取总的(不相干的)ergotropy。此外,我们根据引入的准概率分布提出了框架,该分布对其累积量进行了物理解释,不受测量的侵入性影响,并简化为非相干状态的两点测量方案 (TPM)。最后,
更新日期:2022-07-14
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