Abstract:
We investigate the sensitivity of nonintegrable large-spin quantum lattices to small perturbations
with a particular focus on the time reversal experiments known in statistical physics as “Loschmidt
echoes” and in nuclear magnetic resonance (NMR) as “magic echoes.” Our numerical simulations
of quantum spin-7 1
2
clusters indicate that there is a regime, where Loschmidt echoes exhibit nearly
exponential sensitivity to small perturbations with characteristic constant approximately equal to
twice the value of the largest Lyapunov exponent of the corresponding classical spin clusters. The
above theoretical results are verifiable by NMR experiments on solids containing large-spin nuclei.