title: An entanglement-enhanced microscope.
abstract: Among the applications of optical phase measurement, the differential interference contrast microscope is widely used for the evaluation of opaque materials or biological tissues. However, the signal-to-noise ratio for a given light intensity is limited by the standard quantum limit, which is critical for measurements where the probe light intensity is limited to avoid damaging the sample. The standard quantum limit can only be beaten by using N quantum correlated particles, with an improvement factor of √N. Here we report the demonstration of an entanglement-enhanced microscope, which is a confocal-type differential interference contrast microscope where an entangled photon pair (N=2) source is used for illumination. An image of a Q shape carved in relief on the glass surface is obtained with better visibility than with a classical light source. The signal-to-noise ratio is 1.35±0.12 times better than that limited by the standard quantum limit.
authors.affiliation: 1] Research Institute for Electronic Science, Hokkaido University, N20W10, Kita-Ward Sapporo 001 0020, Japan [2] The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567 0047, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ono
authors.forename: Ryo
authors.initials: R
authors.lastname: Okamoto
authors.forename: Shigeki
authors.initials: S
authors.lastname: Takeuchi
mesh_terms: D008853:Microscopy / Q000295:instrumentation*; D018625:Microscopy, Atomic Force; D018613:Microscopy, Confocal; D008857:Microscopy, Interference; D017785:Photons; D059629:Signal-To-Noise Ratio