Local Control of Macroscopic Properties in Isolated Many-body Quantum Systems

ended

Studies of many-body quantum systems in the last century have been mainly focussed on equilibrium properties; the systems of interest were typically coupled to an environment, which brings about relaxation after short times. The situation changed with the advent of experiments on clouds of ultra-cold, trapped atoms. These are by design almost isolated, and allow for investigations into nonequilibrium dynamics before the onset of dissipative processes. The characterization of such dynamics is now a main frontier of theoretical physics. One of the most exciting phenomena observed was the emergence of a new kind of relaxation, not caused by dissipation. The system acts as its own bath and at late times it is as if the state were prepared at a different temperature, or, especially in low-dimensional systems, in some exotic state of matter. Recently, some progress has been made in extending this picture to inhomogeneous systems. In particular, an exceptional phenomenon was pointed out: a localized perturbation can have global effects on the stationary properties of the observables. LoCoMacro is born of this observation and has the ultimate aim of finding novel ways to control the macroscopic properties of a nonequilibrium state by acting on a small part of the system. We address the fundamental questions of relaxation and emergence of nonequilibrium steady states in the presence of inhomogeneities; we study the effects of localized perturbations on the key elements of the dynamics, as the conservation laws. In integrable models we use the most advanced analytic techniques to obtain exact results, e.g., for correlation functions and entanglement measures. More generally, we rely on state-of-the-art numerical simulations. For the defining characteristics of the models studied, LoCoMacro creates a bridge between two fascinating topics: thermalization in homogeneous systems and many-body localization in disordered ones.