Many-Body Quantum Interference and the Saturation of Out-of-Time-Order Correlators

Out-of-time-order correlators (OTOCs) have been proposed as sensitive probes for chaos in interacting quantum systems. They exhibit a characteristic classical exponential growth, but saturate beyond the so-called scrambling or Ehrenfest time tau(E) in the quantum correlated regime. Here we present a path-integral approach for the entire time evolution of OTOCs for bosonic N-particle systems. We first show how the growth of OTOCs up to tau(E) = (1/lambda) log N is related to the Lyapunov exponent lambda of the corresponding chaotic mean-field dynamics in the semiclassical large-N limit. Beyond tau(E), where simple mean-field approaches break down, we identify the underlying quantum mechanism responsible for the saturation. To this end we express OTOCs by coherent sums over contributions from different mean-field solutions and compute the dominant many-body interference term amongst them. Our method further applies to the complementary semiclassical limit h -> 0 for fixed N, including quantum-chaotic single-and few-particle systems.