MULTI-TIME CORRELATIONS IN OPEN QUANTUM SYSTEMS

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The study of the dynamics of Open Quantum Systems (OQS) and possible alternatives to quantum mechanics such as collapse models (CM) is fundamental for technological and foundational developments.Typically, the dynamics is studied focusing on single-time expectation values of observables of the system. However, single-time expectation values provide only a partial description of the underpinning dynamics hence, multi-time correlation functions (MTCF) need to be considered for a more complete picture.The goal of this project is to provide new insights into OQS dynamics by developing a new methodological framework for the assessment of MTCF that are able to tackle situations ranging from standard environmental decoherence all the way down to exotic CM.The goal will be achieved in 3 steps:1) Introduction of a new non-perturbative technique for computing MTCF in OQS interacting with bosonic baths even in the strong coupling regime and for any temperature of the baths. The technique will be based on replacing the original bath with a surrogate bath described by a finite number of damped harmonic oscillators, making it easier to simulate. The finite network will be engineered to guarantee that the MTCF of the system are the same as those computed using the original bath.2) Computation of MTCF in CM. Hitherto, all computations of MTCF in CM relies on the quantum regression theorem, which is valid under strong assumptions. We will perform for the first time a study of MTCF in CM without assuming the validity of the quantum regression theorem. In contrast to single time expectation values, preliminary analyses suggest that MTCF in CM may differ qualitatively from those in OQS, thus providing new insight in testing CM dynamics against OQS dynamics.3) Application of the results to a specific setup of interest, where measurements of the vibrational modes in a crystalline quartz are performed via non-linear spectroscopy, in collaboration with an experimental group