A Record-Breaking Measurement in Zeptoseconds

Tia Tennariello ‘22

On October 16th, a group of German researchers measured the time it takes for a light particle to pass a single hydrogen atom in a groundbreaking trip of 247 zeptoseconds A trillionth of a billionth of a second , zeptosecond can be written with the number 1 behind 20 zeros.

 Nonetheless, this finding is not the first time scientists have used zeptoseconds. In 2016, physicists at LMU Munich measured the time it took for an excited electron to leave a helium atom: 850 zeptoseconds. Regardless, this new record represents a tremendous advancement in the field of chemical changes; from the first measurement of femtoseconds in 1999, for which Egyptian scientist Ahmed Zewail won a Nobel Prize. Researchers timing a dramatically shorter unit of time signifies a leap in the international venture to measure more and more concise time intervals.

Scientists use zeptoseconds to quantify atomic changes through the photoelectric effect. Theorized by Albert Einstein in 1905, the photoelectric effect describes the occasion in which particles of light dislocate electrons when light hits atoms. Using X-rays, physicists at Goethe University in Germany utilized this theory to measure the light particle’s quick trip past the hydrogen atom. 

The scientists shot X-rays from the PETRA III, a powerful particle accelerator in Deutsches Elektronen-Synchrotron (DESY) in Hamburg. The energy of a light particle, or photon, ejected both electrons from hydrogen. Hydrogen, or H2, is a molecule containing two hydrogen atoms, each with one proton and one electron, so two electrons and two protons total. The first electron shot by the X-ray bumped into the second electron, knocking both of them out of the atom. Electrons have the behavior of both particles and waves, so the waves created from the ejection of the first election collided with the waves created from the ejection of the second electron, similar to a pebble skipping across a surface of water. The interactions between the electrons’ waves result in a measurable wave pattern called an interference pattern.  

To read this interference pattern, the team used an incredibly sensitive particle detector that registers very fast atomic reactions called a Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) reaction microscope. This tool allowed the scientists to establish the positioning of the atom. University of Rodstock researcher Svenn Grundmann explains that, “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,”. This strikingly fast time of 247 zeptoseconds has its delay because, “the electron shell in a molecule does not react to light everywhere at the same time. The time delay occurs because information within the molecule only spreads at the speed of light,” as Professor Reinhard Dörner of Goethe University continues. 

This revolutionary step into the realm of zeptoseconds is merely the most recent. As physics continues to evolve and more tools like COLTRIMS develop, scientists will continue to explore and quantify the molecular world, discovering whatever could possibly be quicker than light through a hydrogen atom.