Entangling dynamics from effective rotor/spin-wave separation in U(1)-symmetric quantum spin models

TL;DR

This paper demonstrates that the non-equilibrium dynamics of U(1)-symmetric quantum spin models, especially the one-axis-twisting model, can be effectively reproduced in systems with power-law interactions through an entanglement mechanism involving rotor and spin-wave separation.

Contribution

It introduces a method to replicate the dynamics of the OAT model in systems with power-law interactions by separating zero-momentum and finite-momentum degrees of freedom, explaining recent numerical results.

Findings

Reproduction of OAT dynamics in dipolar systems

Quantitative explanation of spin squeezing and Schrödinger-cat states

Extension of dynamics understanding to broader quantum simulation models

Abstract

The non-equilibrium dynamics of quantum spin models is a most challenging topic, due to the exponentiality of Hilbert space; and it is central to the understanding of the many-body entangled states that can be generated by state-of-the-art quantum simulators. A particularly important class of evolutions is the one governed by U(1) symmetric Hamiltonians, initialized in a state which breaks the U(1) symmetry -- the paradigmatic example being the evolution of the so-called one-axis-twisting (OAT) model, featuring infinite-range interactions between spins. In this work we show that the dynamics of the OAT model can be closely reproduced by systems with power-law-decaying interactions, thanks to an effective separation between the zero-momentum degrees of freedom, associated with the so-called Anderson tower of states, and reconstructing a OAT model; and finite-momentum ones, associated with spin-wave excitations. This mechanism explains quantitatively the recent numerical observation of spin squeezing and Schr\"odinger-cat generation in the dynamics of dipolar Hamiltonians; and it paves the way for the extension of this observation to a much larger class of models of immediate relevance for quantum simulations.