Supersensitive polarization microscopy using NOON states of light.

A quantum polarized light microscope using entangled NOON states with N=2 and N=3 is shown to provide phase supersensitivity beyond the standard quantum limit. We constructed such a microscope and imaged birefringent objects at a very low light level of 50 photons per pixel, where shot noise seriously hampers classical imaging. The NOON light source is formed by combining a coherent state with parametric down-converted light. We were able to show improved phase images with sensitivity close to the Heisenberg limit.