Nonclassicalities and Quantum Control at the Nanoscale

虽然原子尺度物体的量子行为并不令人惊讶，但如果能在更宏观的物体上发现同样奇怪的特征，那将是绝对令人瞩目的。由于量子物理学是我们日常技术的基础，因此扩展其适用范围的重要性怎么强调都不过分。例如，更大的系统（更容易控制）可以在量子信息处理中发挥关键作用。最近，出现了许多新方法来探测纳米级物体的量子本质，换句话说，就是“非经典性”。其中最重要的是自由移动物体的干扰，其中一个Co-I是专家。另一个是PI的早期想法，通过用辅助量子系统控制它们来探测与受限（静止）纳米级物体的叠加。虽然这些方案尚未实现，但鉴于Co-Is之一的一个聪明想法，它们突然开始看起来非常可行，即光学悬浮这些物体，这在很大程度上将它们与环境隔离开来，并防止退相干-这是一种导致量子特征不可逆转地消亡的现象。在上述背景下，我们提出了一个项目，旨在将自旋耦合到纳米级物体，以控制它们的量子运动，并对自由和被困的中尺度物体的非经典性进行补充测试。由PI和Co-I领导的理论，都是量子光学和信息互补领域的专家，将概述上述实验的适当策略，并探索利用这些系统最终造福于量子信息处理。与我们所知道的其他世界范围的努力相反，我们将避免广泛的冷却和制备高质量的光学腔。这种策略有望为我们在探测几个量子属性方面提供显着的竞争优势，而这些量子属性实际上并不需要上述方法。一个实验性的Co-I自旋操纵将使我们能够悬浮一个自旋轴承纳米物体，并耦合到其运动的自旋。在干涉和悬浮方面专家Co-Is的存在将使我们能够使用两种有前途但互补的技术，用相同或相似的物体探测量子力学的宏观极限。悬浮物体的重要里程碑包括探测这些系统的叠加原理和量子对易关系的有效性，通过它们的运动，它们的纠缠和它们作为量子步行者和量子计算寄存器的潜力进行单次自旋读出。对于自由物体，我们计划将干涉测量中物体的质量提高几个数量级，在干涉测量过程中对其高度非经典状态进行层析成像，并通过对自旋轴承纳米粒子的干涉测量进行精确的自旋测量。该项目还将探索未来更具挑战性的实验的可行性，例如Stern-Gerlach干涉测量法，以探测自由物体的叠加，以及使用悬浮物体作为纠缠自旋的中介。该项目的最终影响预计将在两个方向：当人们将量子原理应用于纳米级物体时，量子原理的有效性是否有任何限制的基本问题，以及在信息技术中使用这种系统的应用问题。这样的研究也有望通过强调宏观系统的反直觉量子行为来提高公众对科学的兴趣。

While the quantum behaviour of atomic-scale objects is no surprise, it would be absolutely arresting to find the same weird features being displayed by much more macroscopic objects. As quantum physics underpins much of our everyday technology, the importance of stretching its domain of applicability can hardly be overemphasized. For example larger systems (easier to control), could play a key role in quantum information processing.Recently, a number of new methods have become available to probe the quantum nature, in other words the "nonclassicality", of nanoscale objects. One of the foremost is the interference of freely moving objects in which one of the Co-Is is an expert. Another is an early idea by the PI to probe superpositions with confined (stationary) nanoscale objects by controlling them with an auxiliary quantum system. While such schemes are yet to be realised, they have suddenly started to look quite feasible in view of a clever idea by one of the Co-Is, namely to optically levitate such objects, which largely isolates them from their environments and prevents decoherence -- a phenomenon that causes the irreversible demise of quantum features. In the above backdrop, we propose a project that aims at coupling spins to nanoscale objects to control their quantum motion and perform complementary tests of the nonclassicality of free and trapped mesoscale objects. Theory led by the PI and a Co-I, both experts in somewhat complementary areas of quantum optics and information, will outline the appropriate strategies for the above experiments, as well as explore the exploitation of these systems for the eventual benefit of quantum information processing. As opposed to other world-wide efforts that we are aware of, we will avoid both extensive cooling and preparing high quality optical cavities. This strategy is expected to give us significant competitive advantage in probing several quantum attributes for which the above are not really necessary. An experimental Co-I in spin manipulation will enable us to levitate a spin bearing nano object and couple the spin to its motion. The presence of expert Co-Is in both interference and levitation is going to enable us to access two promising yet complementary techniques of probing the macroscopic limits of quantum mechanics with the same or similar objects. Significant milestones for levitated objects include probing the validity of the superposition principle and quantum commutation relations for these systems, single shot spin readout through their motion, their entanglement and their potential as quantum walkers and registers for quantum computation. For free objects, we plan to enhance the mass of objects in interferometry by several orders of magnitude, perform tomography of their highly nonclassical states during interferometry, as well as perform precision spin measurements through the interferometry of spin bearing nano particles. The feasibility of more challenging experiments for the future will also be explored within the project, such as a Stern-Gerlach interferometry to probe superpositions of free objects and the usage of a levitated object as a mediator for entangling spins.The ultimate ramifications of the project are expected to be in two directions: the fundamental question of whether there are any limits to thevalidity of quantum principles when one applies them to nanoscale objects, and the applied issue of the usage of such systems in informationtechnology. Such research is also expected to raise public interest in science by highlighting the counterintuitive quantum behaviour ofmacroscopic systems.