Intertwiner Entanglement on Spin Networks

TL;DR

This paper clarifies the nature of entanglement in spin networks within quantum gravity, distinguishing gauge-invariant from gauge-breaking contributions, and shows that physical entanglement arises from superpositions rather than pure states.

Contribution

It explicitly computes gauge-invariant and gauge-breaking entanglement in spin networks, revealing that physical entanglement stems from superpositions, not pure basis states.

Findings

Gauge-invariant entanglement is distinguished from gauge-breaking contributions.

Pure spin network basis states do not carry physical entanglement.

Physical entanglement arises from superpositions of spins or intertwiners.

Abstract

In the context of quantum gravity, we clarify entanglement calculations on spin networks: we distinguish the gauge-invariant entanglement between intertwiners located at the nodes and the entanglement between spin states located on the network's links. We compute explicitly these two notions of entanglement between neighboring nodes and show that they are always related to the typical $\ln(2j+1)$ term depending on the spin $j$ living on the link between them. This $\ln(2j+1)$ contribution comes from looking at non-gauge invariant states, thus we interpret it as gauge-breaking and unphysical. In particular, this confirms that pure spin network basis states do not carry any physical entanglement, so that true entanglement and correlations in loop quantum gravity comes from spin or intertwiner superpositions.