Nonclassicalities and Quantum Control at the Nanoscale

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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.