Entanglement-free Quantum Systems, Processes and Technologies

Quantum mechanics is one of the most precious scientific gifts of the last century and the theoretical background of an impressive range of applications and peculiar phenomena in complex systems. Notwithstanding, it manifests in manifold complementary, sometimes elusive ways. Thus, it is difficult to firmly establish a boundary between the classical and quantum worlds, i.e. when quantum effects become relevant.

On this hand, the burgeoning field of quantum information provides the tools for challenging the resilience of the quantum postulates and, at the same time, for pushing technology over its inherent limits. It is possible to exploit the power of the superposition principle to improve our ability to store, manipulate and transmit Information. Specifically, the enhancement in performing communication tasks, and more generally information transport, is due to counterintuitive correlations allowed by quantum laws, i.e. "entanglement", which can be shared, for example, between the sender and the receiver of a message.

However, creation and protection of entanglement could be a too demanding condition to be satisfied in macroscopic biological systems and engineering appliances, which have to deal with high temperature and high disorder regimes. In particular, entanglement is typically fragile whenever the system under scrutiny undergoes the detrimental interaction of an external environment. Therefore, it sounds compelling to verify the feasibility of large scale quantum technologies harnessing alternative resources, and to identify the roots of the tangible signatures of quantumness at macroscopic scale. In this project, I investigate the potential of more general and more robust kind of quantum correlations (QC) than entanglement, as a resource for delivering quantum technology and describing quantum effects in complex systems. In particular, I identify three main open questions in which QC play a critical role:

a) First, I shall consider how noise affects our ability to measure and retrieve information from a quantum system. In particular, pilot studies suggest that QC are useful for parameter estimation with mixed probes, allowing to overcome the precision of the classical protocols. I will assess the reliability of QC as the benchmark of quantum gain for metrology tasks in noisy conditions;

b) Then, I will investigate the relation between quantum memory effects and QC in the open quantum systems framework. Under strong coupling conditions, the environment can turn into a resource, inducing coherence revivals and increasing QC in the system under scrutiny. It is critical to clarify the mechanisms underpinning this phenomenon and for which tasks we can take advantage of it;

c) Finally, I shall embark upon a more risky and speculative analysis, by studying how quantum mechanics contributes to characterize complexity. A complex system is loosely defined as an agglomerate of many systems in mutual interaction. Some measures of complexity have been proposed to grasp the degree of structure and organisation of a system. I aim to investigate the interplay between such quantities and measures of quantum correlations (QC and entanglement). Quantum mechanics could bring about a peculiar kind of complexity which is observer dependent and hopefully exploitable as a resource.

The project will be carried out at the University of Oxford in Vedral's group and will pursue the collaboration of UK and worldwide researchers in quantum information, information geometry and complex systems. In spite of the theoretical flavour of the proposal, I will work towards the experimental corroboration of my results. In particular, optical and NMR (nuclear magnetic resonance) systems appear to be ideal settings to test the significance of the expected theoretical outputs of the project.

It is hard to overrate the importance of Quantum Mechanics for global issues as well as our daily life, witnessed by spectacular examples of quantum-based technology as the LASER, and indirect products of blue-skies research on quantum laws, e.g. the development of the WWW.

The research proposal promises to provide clear-cut methodological and conceptual advances in the understanding and exploitation of quantum correlations (QC), which may be the premier resource for the implementation of large scale quantum devices, a scientific goal elected by EPSRC as one of the Physics Grand Challenges to cope with in next 20-40 years.

Thus, the project deliverables may be profitable for UK and worldwide industry and economy. The acquired knowledge will bring about new technology and, more important, will give access to new ways to conceive technology. In particular, the project is tailored to support the quests for:

a) Building quantum computers, quantum simulators and quantum sensing devices (direct contribution by scientific outputs). On this purpose, research on QC is recognised of strategic importance by both academia and industry. Indeed, a grant for studying a model of quantum computation exploiting QC as the main resource has been recently awarded in a EPSRC Big Pitch call by a mixed panel of delegates from UK universities and R&D branch of private companies;

b) Developing efficient environmental and energetic strategies (indirect impact by providing new methodologies). Our planet has finite energetic resources, thus a dramatic change in industrial and environmental policies is going to occur. Understanding how quantum mechanics regulates energy storage and transport mechanisms in solar cells and other renewable energy appliances is pivotal for the success of ambitious initiatives, e.g. the "Desertec" project (http://www.desertec.org/), and more generally for the future sustainability of our economic and social system. Open quantum systems appear to be the ideal paradigm, granted by Nature, to be studied and imitated for such purposes. It is therefore compelling to shed light on their quantum properties, in particular on the phenomena of coherence revivals and memory effects under adverse conditions;

c) A full understanding of the peculiarities of complex systems, which are ubiquitous abstract models employed in the study of Nature and Society, spanning from engineering to social science (direct impact for quantum-related deliverables, indirect benefit with a new theoretical framework and a novel perspective on complexity science overall). The high risk high reward part of my proposal addresses the issue of characterising the interplay between QC and complexity in quantum systems. On a timescale of 10-50 years, the potential implications are fascinating. Quantum mechanics has already shown its predictive and applicative power outside the traditional domain of physics laws, e.g. carrying a new perspective into the rationale of cryptographic protocols and stock market modelling. I will endeavour to pave the way for an efficient description of collective biological and social behaviours by statistical and probabilistic models inspired by quantum laws, where probabilities are replaced by amplitudes.

Moreover, I wish to contribute to the education and the scientific awareness of UK citizens. A 2012 House of Lords report highlights that a shortage of students in scientific subjects is threatening UK economy http://www.publications.parliament.uk/pa/ld201213/ldselect/ldsctech/37/37.pdf. I hope to stimulate interest in science in the social groups targeted by outreach and public engagement activities in University open days, physics and maths societies events and research showcases, e.g. high school and undergraduate students. They will be informed of the current developments of the project and entertained with catchy but fair talks on the potentialities of future quantum technologies.