Entanglement Content of Quasi-Particle Excitations

TL;DR

This paper demonstrates that quasi-particle excitations in many-body systems contribute a universal, additive amount to bipartite entanglement entropy, independent of system details, with implications for quantum information processing.

Contribution

It provides an analytical and numerical framework showing the universal entanglement contribution of quasi-particles across various models and dimensions.

Findings

Quasi-particle excitations add a universal, additive entanglement contribution.

The result applies to free theories and certain integrable models.

Numerical evidence supports the analytical predictions in lattice systems.

Abstract

We investigate the quantum entanglement content of quasi-particle excitations in extended many-body systems. We show that such excitations give an additive contribution to the bi-partite von Neumann and R\'enyi entanglement entropies that takes a simple, universal form. It is largely independent of the momenta and masses of the excitations, and of the geometry, dimension and connectedness of the entanglement region. The result has a natural quantum information theoretic interpretation as the entanglement of a state where each quasi-particle is associated with two qubits representing their presence within and without the entanglement region, taking into account quantum (in)distinguishability. This applies to any excited state composed of finite numbers of quasi-particles with finite De Broglie wavelengths or finite intrinsic correlation length. We derive this result analytically in one-dimensional massive bosonic and fermionic free field theories and for simple setups in higher dimensions. We provide numerical evidence for the harmonic chain and the two-dimensional harmonic lattice in all regimes where excitations have quasi-particle properties. Finally, we provide supporting calculations for integrable spin chain models and other situations without particle production. Our results point to new possibilities for creating entangled states using many-body quantum systems.