Multi-partite entanglement detection with non symmetric probing

TL;DR

This paper develops a method to accurately detect multi-partite entanglement in spin systems under asymmetric probing, correcting errors in traditional criteria and verifying entanglement in experimental data.

Contribution

It introduces a new lower bound for spin squeezing in asymmetrically probed systems and provides a procedure to verify entanglement degree, including tri-partite entanglement.

Findings

Traditional spin squeezing criteria can be erroneous under asymmetric probing

Derived a lower bound on squeezing for separable states with asymmetric probes

Verified tri-partite entanglement in experimental atomic ensemble data

Abstract

We show that spin squeezing criteria commonly used for entanglement detection can be erroneous, if the probe is not symmetric. We then derive a lower bound on squeezing for separable states in spin systems probed asymmetrically. Using this we further develop a procedure that allows us to verify the degree of entanglement of a quantum state in the spin system. Finally, we apply our method for entanglement verification to existing experimental data, and use it to prove the existence of tri-partite entanglement in a spin squeezed atomic ensemble.