Nonclassicalities and Quantum Control at the Nanoscale

Lead Research Organisation: University College London
Department Name: Physics and Astronomy

Abstract

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 the
validity of quantum principles when one applies them to nanoscale objects, and the applied issue of the usage of such systems in information
technology. Such research is also expected to raise public interest in science by highlighting the counterintuitive quantum behaviour of
macroscopic systems.

Planned Impact

The research proposed here falls into the category of fundamental physics, and as such is primarily academic in nature. While it is difficult to quantify the impact of this research in terms of economic value it will have value and impact. Three principal types of impact have been identified: enhancing the knowledge base that underpins our technological achievements, engaging the public with science and working scientists and training of the next generation in transferable skills valued by academia and industry.

While the nonclassicalities studied in this project may not be commercially viable within a few years but we think that there is a very good potential for the quantum technology and nonclassicalities we study to be useful in one form or another. For example, the ability to measure small mechanical displacements and forces that are required in this research may find applications in sensing. Besides, a significant section of our work will be directed towards quantum information technology, and thereby may have a bearing on the broader issue of storage and processing of information in NEMS, for miniaturised information processors in general. Surely the understanding of their quantum attributes, as this project proposes to do, is pivotal to exploiting them optimally in any form of information technology. Beyond the above, for designing any nanotechnological device, be it a motor or a small engine, we will need to thoroughly understand the extent to which they should be modelled quantum mechanically.

We collaborate with large and small companies that are aligned to our research. For example, GWM has just obtained an EU grant for EUR2.5M which will be shared between two universities, two small-medium enterprises and Agilent (a high-tech company with revenues of over USD4B per year). Agilent are well-placed to commercialize a range of possible technologies that could emerge from our research. Within this current project, GWM will extend his work with E6 (a UK-based company with over 3000 employees), who develop high-tech applications of diamonds. E6 have been providing GWM with research-grade diamonds containing spin qubits for one year, and would be keen to bring diamond qubits to market if possible.

The second principal area of impact for our research is in engaging the public with science. We have substantial experience in this area. We have given talks related to our research on quantum physics in high schools and published popular science articles. We present at university open days, to potential students as well as their parents. These activities not only attract students, but also increase public awareness of science. The centre for doctoral training at Imperial, directed by MSK, organises a project with secondary school students to build physics machines and presents their quantum magic show for a large general audience (hundreds of general audience for the January show in 2011). One of co-Is was part of the team which brought the exhibit ``Schroedinger's Cat on a Silicon Chip" to the Royal Society Summer Science Exhibition. The exhibition attracted 6000 people over the week it was running.

Finally, this project will provide training and development opportunities for young researchers. In our project, the students will learn not only the skills needed individually for experiments and theory but also skills on how the two work together. Presentation and writing skills will be honed as they prepare reports of their work and present talks and posters. Furthermore, the four-site structure of the project will teach teamwork and collaborative skills. All of these skills are transferable and highly valued in industry. In fact, such skills, plus computer programming (numerical) skills, critical thinking skills, which are instilled during research training, have enabled previous students of the investigators to make successful moves to space agency, finance, consultancy etc. in the private sector.

Publications

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Description We have found how to place a nano-scale levitated mass in a quantum superposition of states: a so called Schroedinger's Cat state and verify its quantum behaviour. Also the gravitational field may be interferometrically detected using such a scheme.
We have found how to increase the length scales of superposition
by free flight versions of the above scheme, as well as ways to detect the violation of quantum realism for macroscopic objects through Leggett-Garg inequalities on macroscopic masses.
Additionally, experiments on levitating nano-diamonds with NV centres have been performed, but the diamonds were graphitising. Proposals for matter wave interferometry with large nano-particles have been developed, as well as the methods to probe possible modifications to quantum mechanics in the frequency domain. We have found away to demonstrate the violation of macro-realism by levitated/trapped objects. We have also demonstrated squeezing operations on trapped levitated particles.
Exploitation Route To extend quantum mechanics to more and more macroscopic systems, and ultimately identify any breakdown of quantum mechanics. Use of quantum components in engineering new low energy devices is one direction in which further research can be made. Additionally, the gravimetry can potentially be developed further to create new sensing technology.
Sectors Aerospace, Defence and Marine,Electronics,Energy

 
Description Duality experiment 
Organisation National Institute of Meteorological Research (INRIM)
Country Italy 
Sector Public 
PI Contribution I provided an outline for a dualism experiment with entangled photons.
Collaborator Contribution The partners performed the experiment.
Impact A paper has resulted (published).
Start Year 2015
 
Description LGI Collaboration 
Organisation Bose Institute
Country India 
Sector Academic/University 
PI Contribution I have thought about the problem of how to test the violation of macro-realism for a levitated object.
Collaborator Contribution The partner formulated a non-classicalty test for harmonic oscillators.
Impact Paper written. In submission now in journal. This is not multi-disciplinary.
Start Year 2013