Speaker
Description
While thermalization in isolated quantum many-body systems can be explained by the eigenstate thermalization hypothesis, its process can be nonmonotonic depending on an initial state. In this talk, we propose a numerical method to construct a low-entangled initial state that creates a “burst”——a transient deviation of an expectation value of an observable from its thermal equilibrium value——at a designated time. Our method utilizes the density matrix renormalization group algorithm to find such a state within the matrix product state manifold. 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 employ a local random quantum circuit to 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. Due to the low-entangled nature of the initial state, our predictions can be tested with programmable quantum simulators. Ref: S. Yamada, A. Hokkyo, and M. Ueda, arXiv:2602.09665 [quant-ph] (2026).