By combining a squeezed propagating microwave field and an unsqueezed vacuum field on a hybrid (microwave beam-splitter), we generate entanglement between the two output modes. We verify that we have generated entangled states by making independent and efficient single-quadrature measurements of the two output modes. We observe the entanglement witness EW=−0.263−0.036+0.001 and the negativity N=0.0824−0.0004+0.01 with measurement efficiencies at least 26±0.1% and 41±0.2% for channel~1 and 2 respectively. These measurements show that the output two-mode state violates the separability criterion and therefore demonstrate entanglement. This shared entanglement between propagating microwaves provides an important resource for building quantum networks with superconducting microwave systems.
@article{arxiv.1502.03884,
title = {Generating and verifying entangled itinerant microwave fields with efficient and independent measurements},
author = {H. S. Ku and W. F. Kindel and F. Mallet and S. Glancy and K. D. Irwin and G. C. Hilton and L. R. Vale and K. W. Lehnert},
journal= {arXiv preprint arXiv:1502.03884},
year = {2015}
}