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.
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