A scheme of bipartite microwave polarization entanglement based on Josephson mixer

The basic principles for preparation and detection of continuous variable polarization entanglement in quantum optics, as well as the generalized criterion of bipartite polarization entanglement, are briefly introduced. Based on theories and experiments in quantum optics, a scheme of bipartite quantum microwave polarization entanglement is proposed and simulated. Inseparability of Stokes vector as I(Ŝ1,Ŝ2) and I(Ŝ2,Ŝ3) are obtained in order to witness the polarization entanglement in 100 MHz operation bandwidth of Josephson mixer. Furthermore, relations between inseparability I and squeezing parameter r as well as amplitude ratio Q are discussed respectively. The results show that I(Ŝ1,Ŝ2) is sensitive of the variance of Q, while I(Ŝ2,Ŝ3) seems to be sensitive of the variance of r. Meanwhile, I(Ŝ1,Ŝ2) remains above 1 in the paper, while I(Ŝ2,Ŝ3) is on the contrary well below 1. It can be concluded that Ŝ2 and Ŝ3 of Stokes vectors are inseparable, which means that output signals Êa and Êb of the scheme exhibit bipartite entanglement in polarization. The best entanglement appears at 70 MHz or so with the minimum I(Ŝ2,Ŝ3) value of 0.25. Apart from these, precision of witness for polarization entanglement and quadrature entanglement is compared. Polarization entanglement appears to be easier and more precise to witness according to our research. Keywords: Quantum microwave, Bipartite polarization entanglement, Josephson mixer, Stokes vectors, Inseparability