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.
An electrical circuit consisting of two capacitively coupled inductive loops, each interrupted by a Josephson junction, is analyzed through the classical RSCJ model. The same circuit has recently been studied experimentally and the results were used
to demonstrate quantum mechanical entanglement in the system by observing the correlated states of the two inductive loops after initial microwave perturbations. Our classical analysis shows that the observed phenomenon exists entirely within the classical RSCJ model, and we provide a detailed intuitive description of the transient dynamics responsible for the observations.
