Is state tomography an unambiguous test of quantum entanglement?

TL;DR

This paper argues that state tomography alone cannot definitively confirm quantum entanglement, demonstrating that classical models can replicate experimental results previously attributed to quantum phenomena.

Contribution

It offers a classical interpretation of experiments claiming to demonstrate entanglement, challenging the assumption that state tomography alone confirms quantum entanglement.

Findings

Classical circuit models can produce density matrices similar to quantum entanglement signatures.

Simulation results match experimental data previously interpreted as quantum entanglement.

Classical explanations may suffice for certain macroscopic quantum system observations.

Abstract

We provide an alternative interpretation of recently published experimental results that were represented as demonstrating entanglement between two macroscopic quantum Josephson oscillators. We model the experimental system using the well-established classical equivalent circuit of a resistively and capacitively shunted junction. Simulation results are used to generate the corresponding density matrix, which is strikingly similar to the previously published matrix that has been declared to be an unambiguous demonstration of quantum entanglement. Since our data are generated by a classical model, we therefore submit that state tomography cannot be used to determine absolutely whether or not quantum entanglement has taken place. Analytical arguments are given for why the classical analysis provides an adequate explanation of the experimental results.