  We present the first experimental demonstration of quantum-enhanced detection
at x-ray wavelengths. We show that x-ray pairs that are generated by
spontaneous down-conversion can be used for the generation of heralded x-ray
photons and measure directly the sub-Poissonian statistics of the single
photons by using photon number resolving detectors. We utilize the properties
of the strong time-energy correlations of the down converted photons to
demonstrate the ability to improve the visibility and the signal-to-noise ratio
of an image with a small number of photons in an environment with a noise level
that is higher than the signal by many orders of magnitude. In our work we
demonstrate a new protocol for the measurement of quantum effects with x-rays
using advantages such as background free measurements that the x-ray regime
offers for experiments aiming at testing fundamental concepts in quantum
optics.
