Department of Applied Physics, University of Geneva, 1211 Geneva 4, Switzerland.
Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria.
Phys Rev Lett. 2019 Oct 25;123(17):170605. doi: 10.1103/PhysRevLett.123.170605.
Cooling quantum systems is arguably one of the most important thermodynamic tasks connected to modern quantum technologies and an interesting question from a foundational perspective. It is thus of no surprise that many different theoretical cooling schemes have been proposed, differing in the assumed control paradigm and complexity, and operating either in a single cycle or in steady state limits. Working out bounds on quantum cooling has since been a highly context dependent task with multiple answers, with no general result that holds independent of assumptions. In this Letter we derive a universal bound for cooling quantum systems in the limit of infinite cycles (or steady state regimes) that is valid for any control paradigm and machine size. The bound only depends on a single parameter of the refrigerator and is theoretically attainable in all control paradigms. For qubit targets we prove that this bound is achievable in a single cycle and by autonomous machines.
冷却量子系统可以说是与现代量子技术相关的最重要的热力学任务之一，从基础的角度来看也是一个有趣的问题。因此，毫不奇怪，已经提出了许多不同的理论冷却方案，它们在假设的控制范式和复杂性上有所不同，并且在单个循环或稳态极限下运行。从那时起，量子冷却的界限就成为了一个高度依赖上下文的任务，有多种答案，没有一个普遍的结果可以独立于假设。在这封信中，我们为无限循环（或稳态范围）下的量子系统冷却导出了一个通用的界限，该界限适用于任何控制范式和机器尺寸。该界限仅取决于制冷机的单个参数，并且在所有控制范式中都具有理论可实现性。对于量子比特目标，我们证明该界限可以在单个循环和自主机器中实现。
