We report a nonlocal interferometer capable of detecting entanglement and identifying Bell states statistically. This is possible due to the interferometer's unique correlation dependence on the anti-diagonal elements of the density matrix, which have distinct bounds for separable states and unique values for the four Bell states. The interferometer consists of two spatially separated balanced Mach-Zehnder or Sagnac interferometers that share a polarization entangled source. Correlations between these interferometers exhibit non-local interference, while single photon interference is suppressed. This interferometer also allows for a unique version of the CHSH-Bell test where the local reality is the photon polarization. We present the relevant theory and experimental results.
@article{arxiv.1408.5310,
title = {A nonlocal polarization interferometer for entanglement detection},
author = {Brian P. Williams and Travis S. Humble and Warren P. Grice},
journal= {arXiv preprint arXiv:1408.5310},
year = {2016}
}