Spatial entanglements of macroscopic quantum systems are proposed. The which-path uncertainty of a single photon passing through a beam splitter is transformed into the which-path uncertainty of two macroscopic fields via two quantum nondemolition measurements. The macroscopic fields are nonlocally correlated.
J. C. Howell and J. A. Yeazell, Entangling Macroscopic Quantum States, Phys. Rev. A 62(1), 012102. https://doi.org/10.1103/PhysRevA.62.012102
American Physical Society