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  • Borgonovi, Fausto; Izrailev, Felix M; Santos, Lea F

    arXiv.org, 03/2019
    Paper, Journal Article

    We study quench dynamics in the many-body Hilbert space using two isolated systems with a finite number of interacting particles: a paradigmatic model of randomly interacting bosons and a dynamical (clean) model of interacting spins-\(1/2\). For both systems in the region of strong quantum chaos, the number of components of the evolving wave function, defined through the number of principal components \(N_{pc}\) (or participation ratio), was recently found to increase exponentially fast in time Phys. Rev. E 99, 010101R (2019). Here, we ask whether the out-of-time ordered correlator (OTOC), which is nowadays widely used to quantify instability in quantum systems, can manifest analogous time-dependence. We show that \(N_{pc}\) can be formally expressed as the inverse of the sum of all OTOC's for projection operators. While none of the individual projection-OTOC's shows an exponential behavior, their sum decreases exponentially fast in time. The comparison between the behavior of the OTOC with that of the \(N_{pc}\) helps us better understand wave packet dynamics in the many-body Hilbert space, in close connection with the problems of thermalization and information scrambling.