Spreading of information in out-of-equilibrium quantum systems with variable-range interactions

Laurent Sanchez-Palencia

Laurent Sanchez-Palencia

Laurent Sanchez-Palencia

Keshav Das Agarwal, Debkanta Ghosh, Pritam Halder +1 more

A spin-$s$ variable-range interacting Ising model may display qualitatively different behaviors depending on the fall-off rate of the interactions, as already seen in equilibrium studies of spin-1/2 systems. We propose a dynamical method using weighted graph states, generated through time evolution that confirms the existence of the transition point in the fall-off rate for the spin-$s$ Ising model. Moreover, the dependence of local dimension on information spreading and multipartite entanglement profile in this model remains unclear, which we establish here. In particular, our analysis shows that the maximum of genuine multipartite entanglement (GME) with the fall-off rate serves as a clear indicator of the information spreading, which aligns with changes in the profile of the Lieb-Robinson bound. Further, in the case of an open chain, the spread of information is related to the divergence in the first derivative of GME. Additionally, we validate this signature by performing a scaling analysis of the time-averaged mutual information.

Silvia Pappalardi

Over the past twenty years, experimental and technological progresses have motivated a renewed attention to the study of non-equilibrium isolated many-body systems, leading to a relatively well-established paradigm in the case of local Hamiltonians. In the present thesis, I have used quantum information theoretical tools to study out-of-equilibrium dynamics, with particular attention on long-range interacting many-body systems. I have explored the dynamics of bipartite and multipartite entanglement in connection to chaos and scrambling in various long-range (clean and disordered) models. The results contained in this thesis contribute to establishing semi-classical tools as powerful techniques for the description of the quantum information spreading in long-range systems. I have further considered a different, yet connected question, concerning the multipartite entanglement structure of chaotic eigenstates and its generic evolution.

Fergus Barratt