Quantum spin fluctuations in dynamical quantum phase transitions*

Dynamical quantum phase transitions (DQPTs), criticality in the transient time response of a many-body system being brought out of equilibrium, have been an active research area in the recent decade. Despite the plethora of studies, the understanding of the role quantum fluctuations played in DQPTs is still incomplete. In this talk, we will address this question by investigating the spin dynamics, as quantified by the spin squeezing parameter, around DQPT in quenched interacting spin systems. We find that the spin-squeezing parameter attains a maximum in the vicinity of DQPTs in most quench cases and further unveiled the dominant spin-spin correlation aligns with the direction of the spin interactions in the post-quench phase. These findings provide insight into the intricate dynamics of spin systems during DQPTs and their connection with the equilibrium phase diagrams.