https://www.sciencealert.com/physicists-have-managed-to-create-quantum-x-rays
"The relationships between photon pairs on quantum scales can be exploited to create sharper, higher-resolution images than classical optics . . . But the technical challenges of generating entangled photons in X-ray wavelengths are considerably greater than for optical light . . . hey used a technique called quantum illumination to minimise background noise. Usually, this uses entangled photons, but weaker correlations work, too. Using a process called parametric down-conversion (PDC), the researchers split a high-energy - or "pump" - photon into two lower-energy photons, called a signal photon and an idler photon. . . . Currently, determining whether the photons are entangled is the next step. That would require the photons' arrival at the detectors to be measured within attosecond scales, which is beyond our current technology."
