CHARACTERIZATION AND ENGINEERING OF QUANTUM SYSTEMS

Characterization and engineering are the basis for any technological development that aspires to exploit scientific breakthroughs and novel physical phenomena. Nowadays, it is impossible to ignore the exceptional results and developments that quantum mechanics, in combination with information theory, has developed in recent decades. This thesis is part of this line of research, with the scope of providing new results regarding quantum sensing and quantum control. Firstly, the need for quantum systems to work in well-established temperature regimes has brought much attention to quantum thermometry. Establishing new methods to probe temperatures of fragile systems is critical for the development of trustworthy quantum devices. Decoherence is detrimental for many tasks, but the paradigm of quantum probing offers a new perspective on it. Instead of considering it as an undesirable phenomenon, we exploit this inherent fragility to probe features of the environment. Secondly, the ability to jointly estimate parameters is of pivotal importance in several fields, from imaging to gravitational wave detectors. The measurement of quantum systems has several limitations: these might come from an external noisy environment, or they might be quantum in nature, such as the impossibility of simultaneously measuring non-commutative observables. The fundamental understanding of quantum incompatibility in metrology can be impactful both at the foundational and applicative levels. We provide results regarding the quantification of measurement incompatibility, while also studying probe incompatibility, optimizing the initial preparation for the characterization of non-linearities in quantum optical devices. Finally, the last contribution of this PhD thesis consists of a new proposal for quantum search with continuous-time quantum walks. The proposed protocol combines three different fields of research, i.e. continuous measurement, feedback and quantum walks, to provide a novel method to perform quantum search protocols on graphs.