First appearance of quasiprobability negativity in quantum many-body dynamics

TL;DR

This paper introduces the first-time negativity (FTN) of quasiprobability distributions as a new dynamical indicator of nonclassical behavior in quantum many-body systems, demonstrating its effectiveness in the Ising chain.

Contribution

The paper presents the first systematic study of quasiprobability negativity emergence in many-body dynamics and introduces FTN as a practical, experimentally accessible measure.

Findings

FTN discriminates between different dynamical regimes in the Ising chain.

FTN's behavior is affected by temperature and integrability breaking.

FTN reveals spatio-temporal spreading of quantum incompatibility.

Abstract

Quasiprobability distributions capture aspects of quantum dynamics that have no classical counterpart, yet the dynamical emergence of their negativity in many-body systems remains largely unexplored. We introduce the \emph{first-time negativity} (FTN) of the Margenau-Hill quasiprobability as a dynamical indicator of when local measurement sequences in an interacting quantum system begin to exhibit genuinely nonclassical behavior. Using the Ising chain, we show that FTN discriminates clearly between interaction-dominated and field-dominated regimes, is systematically reshaped by temperature, and responds sensitively to the breaking of integrability. When measurements are performed on different sites, FTN reveals a characteristic spatio-temporal structure that reflects the finite-time spreading of operator incompatibility across the lattice. We further compare the numerical onset of negativity with a recently proposed quantum speed limit (QSL) for quasiprobabilities, which provides a geometric benchmark for the observed dynamics. Our results identify FTN as a practical and experimentally accessible probe of real-time quantum coherence and contextuality, directly suited to current platforms capable of sequential weak and strong measurements.