We investigate a two-qubit open Rabi model, focusing on local ergotropy-the maximum extractable work by acting solely on the two qubits-within a parameter regime where a Berezinskii–Kosterlitz–Thouless dissipative phase transition occurs. First, we aim to define a protocol for charging, storing, and discharging the two-qubit subsystem, interpreted as the working principle of an open quantum battery. Second, we examine the impact of the phase transition on ergotropy and identify potential markers. To achieve these goals, we construct an ad-hoc charging unitary operator, leveraging our knowledge of the ground state near the transition to bring it into a decoherence-free state (DFS) during storage. Using state-of-the-art numerics based on matrix product state representation, we reveal that high couplings to an external bath approximately double the local ergotropy immediately post-charging. Over time we observe oscillatory behaviors in ergotropy and its fluctuations, which undergo significant changes near the transition, signaling its occurrence. Furthermore, we optimize local ergotropy over time using a physically inspired ansatz, enabling work extraction at a generic time (local ergotropy never reaches zero). Our work proposes a tunable, experimentally realizable protocol for work extraction, leveraging DFS and phase transitions. Additionally, it sheds light on the complex interaction between local ergotropy and quantum phase transitions.

中文翻译：

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局部测角效应及其在耗散量子相变中的波动


我们研究了一个双量子比特开放 Rabi 模型，重点关注局部 ergotropy-仅作用于两个量子比特的最大可提取功——在发生 Berezinskii-Kosterlitz-Thouless 耗散相变的参数范围内。首先，我们的目标是定义一个用于对双量子比特子系统进行充电、存储和放电的协议，该协议被解释为开放量子电池的工作原理。其次，我们检查相变对 ergotropy 的影响并确定潜在的标志物。为了实现这些目标，我们构建了一个临时充电幺正算子，利用我们对过渡附近基态的了解，使其在存储期间进入无退相干状态 （DFS）。使用基于矩阵乘积状态表示的最先进的数值，我们揭示了与外部浴槽的高耦合在充电后立即使局部测厚能力增加约两倍。随着时间的推移，我们观察到 Ergotropy 及其波动的振荡行为，这些波动在转变附近发生显着变化，标志着它的发生。此外，我们使用物理启发的 ansatz 随着时间的推移优化局部 Ergotropy，从而在通用时间实现功提取（局部 Antoytropy 永远不会达到零）。我们的工作提出了一种可调谐的、实验上可实现的功提取协议，利用 DFS 和相变。此外，它还阐明了局部 metatropy 和量子相变之间的复杂相互作用。