Repeated backaction evading measurements: demonstration of a noiseless optical bus

Summary form only given. We report here repeated back action evading (BAE) experiments that clearly demonstrate all quantum nondemolition (QND) features for repeated measurements. An important feature is that each of the two BAE setups, based on pulsed type-II parametric amplifiers, also have performances that are the best achieved so far, and therefore make this demonstration more convincing. The conditional variance of the signal at the output of the first device measurement is given.