Emergence of Light Cones in Long-range Interacting Spin Chains Is Due to Destructive Interference

TL;DR

This paper explains that light cones in long-range quantum spin chains emerge due to destructive interference among quantum effects, which suppresses entanglement outside the light cone, revealing a new physical mechanism for locality.

Contribution

It introduces a novel interference-based mechanism for the emergence of light cones in long-range interacting quantum systems, advancing understanding of quantum locality.

Findings

Destructive interference suppresses entanglement outside the light cone.

Reducing interaction range increases entanglement transport speed.

Interference is necessary for light cone formation.

Abstract

Despite extensive research on long-range interacting quantum systems, the physical mechanism responsible for the emergence of light cones remains unidentified. This work presents a novel perspective on the origins of locality and emergent light cones in quantum systems with long-range interactions. We identify a mechanism in such spin chains where effective entanglement light cones emerge due to destructive interference among quantum effects that entangle spins. Although long-range entangling effects reach beyond the identified light cone, due to destructive interference, entanglement remains exponentially suppressed in that region, ultimately leading to the formation of the light cone. We demonstrate that this interference not only drives but is also necessary for the emergence of light cones. Furthermore, our analysis reveals that reducing the interaction range weakens this interference, surprisingly increasing the speed of entanglement transport, an effect that opens new experimental opportunities for investigation.