Center for Theoretical Physics of Complex Systems, Institute for Basic Science (IBS), Daejeon - 34126, Korea.
Basic Science Program, Korea University of Science and Technology (UST), Daejeon-34113, Korea.
Phys Rev Lett. 2023 May 26;130(21):210401. doi: 10.1103/PhysRevLett.130.210401.
Energy extraction is a central task in thermodynamics. In quantum physics, ergotropy measures the amount of work extractable under cyclic Hamiltonian control. As its full extraction requires perfect knowledge of the initial state, however, it does not characterize the work value of unknown or untrusted quantum sources. Fully characterizing such sources would require quantum tomography, which is prohibitively costly in experiments due to the exponential growth of required measurements and operational limitations. Here, we therefore derive a new notion of ergotropy applicable when nothing is known about the quantum states produced by the source, apart from what can be learned by performing only a single type of coarse-grained measurement. We find that in this case the extracted work is defined by the Boltzmann and observational entropy in cases where the measurement outcomes are, or are not, used in the work extraction, respectively. This notion of ergotropy represents a realistic measure of extractable work, which can be used as the relevant figure of merit to characterize a quantum battery.
能量提取是热力学的一项核心任务。在量子物理学中，负嫡衡量的是在循环哈密顿控制下可提取的功的数量。然而，由于完全提取需要对初始状态有完美的了解，因此它不能描述未知或不可信的量子源的功值。要完全描述这样的源，需要进行量子层析成像，而由于所需测量的指数增长和操作限制，这在实验中是非常昂贵的。因此，我们在这里推导出了一个新的负嫡概念，当除了通过仅执行一种类型的粗粒测量可以学到的内容之外，对源产生的量子态一无所知时，该概念是适用的。我们发现，在这种情况下，提取的功由玻尔兹曼熵和观测熵定义，具体取决于测量结果是否用于功提取。这个负嫡的概念代表了可提取功的实际度量，可以用作相关的优值来描述量子电池。
