Quantum heat engines as quantum computers

自200年前热机的概念诞生以来，发动机和冰箱等热机一直是热力学的中心点。为了更好地了解这类机器，最终的目标是创造出性能更好、输出功率更高、效率更高的机器。由于热力机器可以建立在越来越小的尺度上，很明显，它们将不可避免地达到量子力学的微观领域，用宏观机器的(经典)热力学的语言来描述它们不再足够。这导致了新的量子热力学理论的产生，该理论试图将这两个现有的理论结合起来。近年来，量子热机的研究在理论和实验上都取得了很大的进展。值得注意的是，如今这些不再只是理论上的概念，而是在使用许多不同的物理平台如钻石中的氮空位中心、核磁共振装置、超冷原子和离子陷阱的实验中实现的。然而，量子热机的多功能性超出了它们作为热机、冰箱或热泵的直接用途。它们可以以新颖的方式应用于创造全新的有用设备，并成为将我们对热机的知识应用于不同物理领域的桥梁。本着这种精神，该项目的主要目标是设计第一个可以执行量子计算算法的量子热机。这将把量子热力学与非常重要的量子计算领域联系起来。有了这个新的热力学视角，量子计算机可以得到更好的理解和长期的优化，这是量子计算机任何大规模应用不可或缺的关键一步。为此，我们有三个目标。首先，我们开始研究量子热机及其效率和功率的涨落，如果量子相干性存在的话。在此基础上，我们将开发协议来实现具有量子热机行程的量子门。我们专注于简单的量子门，它只由一个或两个量子比特组成，作为任何量子计算算法的基本构件。我们将从热力学和量子力学的角度全面研究这些协议，并评估它们的效率和保真度。最后，我们将通过考虑实验参数和场景来详细说明我们的引擎协议，使其更加现实，可以在现有的量子热力学和量子计算实验平台上实现。

Thermal machines like engines and fridges have been a central point of thermodynamics since its conception 200 years ago. The search for a better understanding of such machines was ultimately linked to the goal of creating better-performing machines with higher power output and efficiency. As thermal machines could be built on increasingly smaller scales, it became clear that they would inevitably reach the microscopic domain of quantum mechanics, and it would no longer suffice to describe them in the language of the (classical) thermodynamics of macroscopic machines. This led to the creation of the new theory of quantum thermodynamics, which tries to combine the two existing theories. In recent years, great theoretical and experimental advancements have been made in the study of quantum thermal machines. Strikingly, nowadays these are no longer just theoretical concepts but are implement in experiments using many different physical platforms like nitrogen-vacancy centers in diamond, NMR setups, ultracold atoms, and ion traps. However, the versatility of quantum thermal machines goes beyond their direct usage as heat engines, refrigerators, or heat pumps. They can be applied in novel ways to create completely new useful devices and serve as a bridge to apply our knowledge of thermal machines to different physical fields.In this spirit, the main goal of this project is to design the very first quantum heat engine which can perform quantum computational algorithms. This will connect quantum thermodynamics to the highly important field of quantum computation. With this new thermodynamic perspective, quantum computers can be much better understood and long-term be optimized, which is an indispensable crucial step for any large-scale application of quantum computers. For this, we have three objectives. First, we begin with a study of quantum heat engines and their fluctuations of efficiency and power if quantum coherences are present in the setup. Based on this we will then develop protocols to implement quantum gates with the strokes of a quantum heat engine. We focus on simple quantum gates, consisting of only one or two qubits which serve as the basic building blocks of any quantum computational algorithm. We will fully study these protocols from a thermodynamic and quantum mechanical perspective and assess their efficiency and fidelity. Lastly, we will elaborate on our engine protocols by making them more realistic by taking into account experiment parameters and scenarios, which can be implemented on current experimental platforms in quantum thermodynamics and quantum computation.