Quantum dynamics and entanglement of spins on a square lattice

TL;DR

This paper presents neutron scattering experiments on a two-dimensional quantum antiferromagnet, revealing quantum effects and spin entanglement that challenge classical magnetic descriptions.

Contribution

It provides the first comprehensive experimental evidence of quantum entanglement and non-spin-wave excitations in a 2D square lattice antiferromagnet.

Findings

Detection of a non-spin-wave continuum in neutron scattering data

Evidence of strong quantum effects and entanglement in 2D antiferromagnets

Challenging classical magnetic models with quantum experimental results

Abstract

Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet in many situations, including our everyday encounters with magnetic materials, quantum effects are masked, and it often suffices to think of magnetism in terms of the interaction between classical dipole moments. Whereas this intuition generally holds for ferromagnets, even as the size of the magnetic moment is reduced to that of a single electron spin (the quantum limit), it breaks down spectacularly for antiferromagnets, particularly in low dimensions. Considerable theoretical and experimental progress has been made in understanding quantum effects in one-dimensional quantum antiferromagnets, but a complete experimental description of even simple two-dimensional antiferromagnets is lacking. Here we describe a comprehensive set of neutron scattering measurements that reveal a non-spin-wave continuum and strong quantum effects, suggesting entanglement of spins at short distances in the simplest of all two-dimensional quantum antiferromagnets, the square lattice Heisenberg system.