The ability to generate and manipulate quantum states of light has led to novel measurement techniques, such as quantum imaging and metrology, that have greatly improved our understanding of the quantum world while also laying the groundwork for quantum computing and communication. And yet there has been little progress in extending these concepts to x-ray wavelengths, which could lead to a breadth of new applications such as advanced probes of atomic-scale phenomena. Researchers have begun developing new, bright sources of x-ray photons. However, no one has managed to use these sources to generate photons that exhibit statistics of quantum states of radiation, like in the optical regime. Here, we generate single x-ray photons and show that they do indeed exhibit such statistics.

Using x-ray beams at the RIKEN Spring-8 Center in Japan, we generate pairs of x-ray photons in a diamond crystal. These photons are then recorded by two detectors—since the photons are always generated in pairs, if one photon is detected at one detector, then there must also be exactly one correlated photon at the other detector. This latter photon is therefore a true “single photon,” which obeys the hoped-for statistics of quantum radiation. By placing an object—a thin metal sheet with three parallel slits—in the beam of this photon, we produce an image with a small number of photons in an environment where the noise level is much higher than the signal. This image has a signal-to-noise ratio that is much better compared to classical methods.

Our work could lead to a new platform for tests of fundamental concepts in quantum physics by using the high energy of x-ray photons, and it could also open the door to fascinating applications that address the challenge of radiation damage when using x rays.