Twin entangled beams produced by single-pass parametric down-conversion (PDC) offer the opportunity to detect weak amount of absorption with an improved sensitivity with respect to standard techniques which make use of classical light sources. We propose a differential measurement scheme which exploits the spatial quantum correlation of type II PDC to image a weak amplitude object with a sensitivity beyond the standard quantum limit imposed by shot-noise.
@article{arxiv.0710.0053,
title = {High-sensitivity imaging with multi-mode twin beams},
author = {E. Brambilla and L. Caspani and O. Jedrkiewicz and L. A. Lugiato and A. Gatti},
journal= {arXiv preprint arXiv:0710.0053},
year = {2009}
}