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，但如果在更宏观的物体上发现同样奇怪的特征，那将绝对是引人注目的。由于量子物理学支撑着我们的许多日常技术，扩展其应用领域的重要性怎么强调都不为过。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，有许多新的方法可以用来探测纳米尺度物体的量子性质，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，其中一个合作伙伴是专家。另一个是PI的早期想法，通过辅助量子系统控制受限（静止）纳米级物体来探测它们的叠加态。虽然这样的方案还没有实现，但考虑到其中一个co - i的一个聪明的想法，它们突然开始看起来相当可行，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——一种导致量子特征不可逆转消亡的现象。在上述背景下，我们提出了一个旨在将自旋耦合到纳米尺度物体以控制其量子运动的项目，并对自由和被困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，在量子光学和信息的某些互补领域的专家，将概述上述实验的适当策略，以及探索这些系统的利用，以最终受益于量子信息处理。与我们所知道的其他世界范围的努力相反，我们将避免大量冷却和制备高质量的光学腔。这一策略有望给我们带来显著的竞争优势，在探索几个量子属性时，上面所说的并不是真正必要的。自旋操纵中的实验Co-I将使我们能够悬浮一个带有自旋的纳米物体，并将自旋与其运动耦合起来。干涉和悬浮领域的专家co - i的存在将使我们能够获得两种有前途的互补技术，即用相同或类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交换关系的有效性，通过它们的运动读出单次自旋，它们的纠缠以及它们作为量子行走者和量子计算寄存器的潜力。对于自由物体，我们计划将干涉测量中的物体质量提高几个数量级，在干涉测量中对其高度非经典状态进行断层扫描，以及通过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，例如用斯特恩-格拉赫干涉测量法探测自由物体的叠加，以及使用悬浮物体作为纠缠自旋的介质。该项目的最终结果预计将在两个方向上：当量子原理应用于纳米级物体时，其有效性是否存在任何限制的基本问题，以及在信息技术中使用此类系统的应用问题。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.