Unlocking vacuum entanglement

TL;DR

This paper investigates the entanglement structure in the ground state of harmonic chains and shows how measurements on central modes can unlock enhanced entanglement between distant modes, with implications for experiments and quantum fields.

Contribution

It introduces a method to enhance entanglement between distant modes by measuring central modes, extending the concept to continuous quantum fields.

Findings

Entanglement between end modes diminishes with chain length.

Measuring central modes can significantly increase entanglement.

Enhanced entanglement can be demonstrated in trapped ion experiments.

Abstract

The structure of entanglement in the ground state of the harmonic chain is studied. A class of two-mode squeezed states, useful for this purpose, is identified. The entanglement of the local modes at the ends of the chain, after tracing out the centre, rapidly falls to zero as the length of the chain increases. However, if the central modes are measured, and the result communicated to systems interacting with the outer modes, the latter exhibit greatly enhanced entanglement, including in conditions where none was otherwise available. These ideas can be demonstrated in experiments in trapped ions, among other systems. The extension to the continuous case yields enhanced entanglement extracted from the vacuum state of a bosonic quantum field.