Extreme spin squeezing for photons

TL;DR

This paper demonstrates that polarization-squeezed light can exhibit large-scale multipartite entanglement among photons, observable with current detectors, using spin-squeezing criteria and theoretical modeling.

Contribution

It applies spin-squeezing techniques to quantify multipartite entanglement in polarization-squeezed light, showing that macroscopic entanglement is detectable without post-selection.

Findings

Wineland-criterion polarization squeezing implies large-scale entanglement

N-photon density matrix calculations confirm observable multipartite entanglement

Existing detectors can observe ~1000-partite entanglement with a few dB of squeezing

Abstract

We apply spin-squeezing techniques to identify and quantify highly multi-partite photonic entanglement in polarization-squeezed light. We consider a practical single-mode scenario, and find that Wineland-criterion polarization squeezing implies entanglement of a macroscopic fraction of the total photons. A Glauber-theory computation of the observable N-photon density matrix, with N up to 100, finds that N-partite entanglement is observable despite losses and without post-selection. We estimate that existing detectors could observe $\sim1000$-partite entanglement from a few dB of polarization squeezing.