Their results, published in Nature Photonics, reveal that correlated electrons can cooperate to generate much more energetic X-rays than either electron could produce alone. The breakthrough builds on high-harmonic generation, a process that converts laser light into radiation with frequencies hundreds or even thousands of times higher. In the standard picture of high-harmonic generation, a strong laser field first pulls an electron away from its parent atom. Beyond extending the reach of laboratory X-ray sources, the discovery could turn high-harmonic generation into a sensitive probe of many-electron physics. In the longer term, the ability to generate and control correlated X-ray bursts could help scientists study quantum many-body processes with unprecedented temporal resolution.