# Chaotic dynamical ferromagnetic phase induced by non-equilibrium quantum fluctuations

## TL;DR

This paper explores how quantum fluctuations influence the stability of dynamical phase transitions in a fully-connected quantum Ising model, revealing a chaotic phase with sensitive dependence on initial conditions.

## Contribution

It demonstrates that increasing quantum fluctuations can induce a chaotic dynamical phase, extending the understanding of non-equilibrium quantum phase behavior beyond mean-field predictions.

## Key findings

- Quantum fluctuations cause the dynamical critical point to fan out into a chaotic phase.
- The chaotic phase exhibits strong sensitivity to parameters and initial conditions.
- The phenomenon is likely general for systems with broken discrete symmetry.

## Abstract

We investigate the robustness of a dynamical phase transition against quantum fluctuations by studying the impact of a ferromagnetic nearest-neighbour spin interaction in one spatial dimension on the non-equilibrium dynamical phase diagram of the fully-connected quantum Ising model. In particular, we focus on the transient dynamics after a quantum quench and study the pre-thermal state via a combination of analytic time-dependent spin-wave theory and numerical methods based on matrix product states. We find that, upon increasing the strength of the quantum fluctuations, the dynamical critical point fans out into a chaotic dynamical phase within which the asymptotic ordering is characterised by strong sensitivity to the parameters and initial conditions. We argue that such a phenomenon is general, as it arises from the impact of quantum fluctuations on the mean-field out of equilibrium dynamics of any system which exhibits a broken discrete symmetry.