A system in thermal equilibrium with a bath will generally be in an athermal state, if the system-bath coupling is strong. In some cases, it will be possible to extract work from that athermal state, after disconnecting the system from the bath. We use this observation to devise a battery charging and storing unit, simply consisting of a system, acting as the battery, and a bath. The charging cycle—connect, let thermalize, disconnect, extract work—requires very little external control and the charged state of the battery, being a part of global thermal equilibrium, can be maintained indefinitely and for free. The efficiency, defined as the ratio of the extractable work stored in the battery and the total work spent on connecting and disconnecting, is always $\le 1$, which is a manifestation of the second law of thermodynamics. Moreover, coupling, being a resource for the device, is also a source of dissipation: the entropy production per charging cycle is always significant, strongly limiting the efficiency in all coupling strength regimes. We show that our general results also hold for generic microcanonical baths. We illustrate our theory on the Caldeira-Leggett model with a harmonic oscillator (the battery) coupled to a harmonic bath, for which we derive general asymptotic formulas in both weak and ultrastrong coupling regimes, for arbitrary Ohmic spectral densities. We show that the efficiency can be increased by connecting several copies of the battery to the bath. Finally, as a side result, we derive a general formula for Gaussian ergotropy, that is, the maximal work extractable by Gaussian unitary operations from Gaussian states of multipartite continuous-variable systems.

中文翻译：

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加热辅助充电

如果系统与浴之间的耦合较强，则具有浴的热平衡系统通常将处于非热状态。在某些情况下，将系统与水浴断开连接后，有可能从该非热状态提取功。我们使用此观察结果来设计电池充电和存储单元，该单元仅由充当电池的系统和浴缸组成。充电周期（连接，加热，断开，提取工作）几乎不需要外部控制，并且电池的充电状态（作为全局热平衡的一部分）可以无限期地免费维护。效率始终定义为存储在电池中的可提取功与连接和断开连接所花费的总功之比。$\le \mathrm{1个}$，这是热力学第二定律的体现。此外，耦合是设备的资源，也是耗散的来源：每个充电周期的熵产生始终很重要，从而严重限制了所有耦合强度方案的效率。我们表明，我们的一般结果也适用于通用微规范浴。我们用耦合到谐波浴的谐波振荡器（电池）说明了关于Caldeira-Leggett模型的理论，对于任意欧姆谱密度，我们针对弱和超强耦合机制推导了一般渐近公式。我们表明，通过将电池的多个副本连接到浴池可以提高效率。最后，作为附带的结果，我们导出了高斯遍历性的通用公式，即