Speed matters. When an X-ray photon excites an atom or ion, making a core electron jump onto a higher energy level, a short-lived window of opportunity opens. For just a few femtoseconds, before an electron fills the void in the lower energy level, a second photon has the chance to be absorbed by another core electron, creating a doubly excited state.

Using 5,000 intense X-ray flashes per second, generated by the European XFEL, an international team of scientists has investigated such double core-hole states in highly ionized krypton, using photons that all had nearly the same energy or color.

For their experiments, scientists from European XFEL and the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg as well as six other institutions across Germany, Italy, Portugal, and the United States, used highly charged krypton, Kr²⁶⁺, lacking all but ten of its electrons.

Optical lattice clocks are devices that measure the passing of time via the frequency of light that is absorbed or emitted by laser-cooled atoms trapped in a repeating pattern of light interference known as optical lattice.

These clocks are significantly more precise than classical clocks and could pick up subtle physical phenomena. They could also be used to test the predictions of various physics theories and could help to improve the performance of existing timekeeping, sensing and communication systems.

Researchers at JILA National Institute of Standards and Technology and University of Colorado recently introduced a new strontium atom-based optical lattice clock that achieved unprecedented precision.

Deep underground in southern China, there is a 20,000-ton tank of liquid that can detect neutrinos. Named JUNO, the detector’s first results are in — and they’re very promising.