Operator Growth Bounds from Graph Theory
نویسندگان
چکیده
Let $A$ and $B$ be local operators in Hamiltonian quantum systems with $N $ degrees of freedom finite-dimensional Hilbert space. We prove that the commutator norm $\lVert [A(t),B]\rVert$ is upper bounded by a topological combinatorial problem: counting irreducible weighted paths between two points on Hamiltonian's factor graph. Our bounds sharpen existing Lieb-Robinson removing extraneous growth. In drawn from zero-mean random ensembles few-body interactions, we stronger ensemble-averaged out-of-time-ordered correlator $\mathbb{E}\left[ \lVert [A(t),B]\rVert_F^2\right]$. such Erd\"os-R\'enyi graphs, scrambling time $t_{\mathrm{s}}$, at which $\lvert [A(t),B]\rVert_F=\mathrm{\Theta}(1)$, almost surely $t_{\mathrm{s}}=\mathrm{\Omega}(\sqrt{\log N})$; further $t_{\mathrm{s}}=\mathrm{\Omega}(\log N) to high order perturbation theory $1/N$. constrain infinite temperature chaos $q$-local Sachdev-Ye-Kitaev model any $1/N$; leading order, our bound Lyapunov exponent within 2 known result $q>2$. also speculate implications theorems for conjectured holographic descriptions gravity.
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ژورنال
عنوان ژورنال: Communications in Mathematical Physics
سال: 2021
ISSN: ['0010-3616', '1432-0916']
DOI: https://doi.org/10.1007/s00220-021-04151-6