We pioneered the art of making spatial measurements below the quantum noise limit. All our experiments start with quickest available laser source, NdYAG monolithic lasers operating at 1064 nm (Innolight, Germany)
As a the first step (2001) we investigated the beam displacement using a simple split detector. We analysed the detection modes, which are flipped modes (Gaussian mode with a 180 degree phase shift left to right). By generating the appropriate squeezed light we were able to demonstrate displacement measurements below the QNL.
"Surpassing the Standard Quantum Limit for Optical Imaging Using Nonclassical Multimode Light" N. Treps, U. Andersen, B. Buchler, P. K. Lam, A. Maître, H.-A. Bachor, and C. Fabre, Phys. Rev. Lett. 88, 203601 (2002)
In 2002, we were able to combine two squeezed modes with the laser beam without losses and could show displacement measurement below the QNL in two dimensions simultaneously. (The quantum laser pointer).
"A Quantum Laser Pointer" N. Treps, N. Grosse, W.P. Bowen, C. Fabre, H.-A. Bachor, and P.K. Lam, Science 301: 940-943 15 August 2003
In 2004 we showed that displacement and tilt are conjugate parameters, that they can be detected with perfect efficiency with a spatial homodyne detector and are suitable for the communication of quantum information.
"Quantum measurements of spatial conjugate variables: displacement and tilt of a Gaussian beam" V. Delaubert, N. Treps, C.C. Harb, P.K. Lam, and H.-A. Bachor, Opt. Lett., 31, 1537 (2006)
In 2005 we found a way to generate squeezed light directly in the TEMnk high order modes using special phase matching techniques.
"Generation of squeezing in higher order Hermite-Gaussian modes with an optical parametric amplifier" M. Lassen, V. Delaubert, C.C. Harb, P.K. Lam, N. Treps, H-A. Bachor, J. Eur. Opt. Soc. R. Comm., 1, 06003 (2006)
In 2006 we have built two high order mode squeezers and we are combining them to a pair of spatially entangled beams. We are attempting to make EPR measurements based on the conjugate parameters of beam position and momentum (displacement and tilt), to verify the original case proposed by Einstein Podolsky and Rosen.
Two spatial squeezers