Physicists from Goethe University Frankfurt used this measurement to record how long it takes for a photon to cross a hydrogen molecule - approximately 247 zeptoseconds.
How did scientists discover Zeptosecond?
In order to measure this event, scientists irradiated a hydrogen molecule using X-rays from the PETRA III laser, the most powerful light source of its kind.
The energy of the X-rays was set so that only one photon was needed to send both electrons out of the hydrogen molecule.
This had the effect of skimming the photon across the two electrons. Electrons behave like particles and waves simultaneously, and as such when one electron was ejected, the waves moved the second electron.
The photon bounced one electron out of the molecule, and then the other, a bit like a pebble skipping over the top of a pond. These interactions created a wave pattern called an interference pattern, which Dörner and his colleagues could measure with a tool called a Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) reaction microscope. This tool is essentially a very sensitive particle detector that can record extremely fast atomic and molecular reactions. The COLTRIMS microscope recorded both the interference pattern and the position of the hydrogen molecule throughout the interaction.
"Since we knew the spatial orientation of the hydrogen molecule, we used the interference of the two-electron waves to precisely calculate when the photon reached the first and when it reached the second hydrogen atom," Sven Grundmann, a study co-author at the University of Rostock in Germany, said in a statement as quoted by Live Science.