Investigating quantumness in complex systems under adverse conditions

In order to work properly, the engine of a sports car needs all its parts to work together, following a precise pattern. This means that a complicated ensemble of mechanical parts and electric circuitry has to be engineered in a consistent way. The performances of the car will critically depend on the way this ensemble has been put together. However, in order to improve the efficiency of the engine (and also to repair it when it breaks down), we would like to have access and control over every single small wheel, fuse and piston. Anyone having a car (and enjoying a bit of do-it-yourself mechanical maintenance and repair) knows that this often implies the necessity of put the hands into it , trying to reach exactly a specific component of the engine and check its status and efficiency.This serves us a layman metaphor for the topics and situations addressed in my project, to be developed at Queen's University Belfast, where intricate quantum systems made out of many parties, all mutually interacting and operating under difficult working conditions, are considered and analysed. In order to improve the performances of quantum protocols based on the use of such complex systems, I propose to follow the path that passes through a proper understanding of the way such systems behave. I will look for appropriate configurations of interactions able to optimise the distribution of quantumness within a many-body system and allowing for the minimisation of the influences of the outside world. In fact, these latter are usually detrimental to any quantum behaviour. In order to achieve this all, I will develop proper analytical tools, novel with respect to the approaches that have been used soi far, specifically designed so as to be close to experimental reality. These formal tools will be extended to the numerical domain for the assessment of even more complicated situations.I will consider the case of difficult addressability of specific components participating to the dynamics of a complex system, as well as the situation of a single object whose quantum behaviour cannot be easily revealed. This latter situation can occur because of the system's intrinsic properties, which push it towards classical evolutions, determining the frailty of its quantum state. The aim of this investigation is the design of strategies, based on the engineering of proper couplings with more manipulable auxiliary states, which allow the indirect revelation of nonclassical features in the dynamics of such problematic cases. Both these tasks are extremely timely and important as they approach two points which are at the core of current theoretical and experimental efforts. They are directed towards the extension of control operated at the quantum level to larger systems of strongly correlated particles and to mesoscopic objects operating under more realistic and less technically demanding conditions. The success of the project will provide effective, practically implementable protocols for the enforcement of quantumness into complex devices and its inference, made possible against the classicality induced by uncontrollable interactions with the ubiquitous outer world . Both these targets are pivotal to gather a better understanding of the quantum-to-classical transition and to discover whether it is possible to push the frontiers of quantum evolutions to a realm that is commonly thought to be merely classical.