Quantum spin fluctuations in dynamical quantum phase transitions

TL;DR

This paper investigates the role of quantum spin fluctuations during dynamical quantum phase transitions by analyzing spin squeezing and correlations in quenched spin models, revealing their behavior near critical points.

Contribution

It introduces a combined approach using Loschmidt amplitude and spin-squeezing parameter to study quantum fluctuations in DQPTs, highlighting their dynamics and relation to phase transitions.

Findings

Maximal spin squeezing occurs near DQPTs during quenches between different phases.

Spin correlations align with the preferred direction of post-quench interactions.

Time evolution of spin squeezing varies with different quench scenarios.

Abstract

Quantum phase transitions have long been studied in their relation to quantum fluctuations. These fluctuations can be quantified as the degree of spin squeezing in spin models, where one of the two non-commutative observables breaks the standard quantum limit of measurement by minimizing its uncertainty. However, the understanding of their role in dynamical quantum phase transitions (DQPTs) is still incomplete. In this work, we combine the Loschmidt amplitude, which detects DQPTs, and the spin-squeezing parameter (SSP), the quantification of spin squeezing, to study the spin dynamics in a quenched interacting spin model around DQPT. We show that the extremal, mostly maximal, of SSP occurs near DQPTs when the system is quenched between different phases. These phenomena further unveil the spin correlations during DQPTs, for which the highest contribution aligns with the preferred direction of spin interactions in the post-quenched phase. We also demonstrate the time evolution of SSP differs for various quench scenarios. These findings provide us with physical insights into the dynamics of quantum fluctuations around DQPTs and their relation to the equilibrium phase diagrams.