Tunable many-body burst in isolated quantum systems

TL;DR

This paper introduces a numerical method to create initial states in quantum systems that produce a controlled transient deviation, or burst, in observable behavior, revealing new insights into thermalization and information spreading.

Contribution

The authors develop a novel numerical approach to engineer initial states that generate a tunable burst in quantum observables, advancing understanding of nonmonotonic thermalization.

Findings

A method to produce a controlled burst of magnetization in quantum systems.

The burst occurs on a timescale comparable to quantum scrambling.

Entanglement growth can be slow or negative during the burst.

Abstract

Thermalization in isolated quantum many-body systems can be nonmonotonic, with its process dependent on an initial state. We propose a numerical method to construct a low-entangled initial state that creates a "burst" -- a transient deviation of an observable from its thermal equilibrium value -- at a designated time. We apply this method to demonstrate that a burst of magnetization can be realized for a nonintegrable mixed-field Ising chain on a timescale comparable to the onset of quantum scrambling. Contrary to the typical spreading of information in this regime, the created burst is accompanied by a slow or even negative entanglement growth. Analytically, we show that a burst becomes probabilistically rare after a long time. Our results suggest that a nonequilibrium state is maintained for an appropriately chosen initial state until scrambling becomes dominant. These predictions can be tested with programmable quantum simulators.