Physicists at Frankfurt observed coupled quantum zero-point motion of atoms in a molecule. The team has used the most powerful X-ray laser to capture the out-of-sight, hidden vibrations of atoms inside molecules. This first-ever detection of zero-point motion unravels the fact that atoms move in a synchronized, precise pattern even in their lowest energy level.
According to Heisenberg’s uncertainty principle, we cannot estimate where a particle is and how fast it is moving simultaneously— you can only focus on one parameter. Atomic dance should be chaotic, but it is far from the truth. Atoms follow a strict choreography inside molecules. A molecule is supposed to be completely frozen at absolute zero. However, the molecules never come to rest because the atoms that make them up perform a constant, never-ending silent dance driven by zero-point energy.
These patterns of quantum dance or zero-point movements were considered impossible to measure for a long time. However, scientists at Goethe University Frankfurt and partner institutions have managed to successfully record the precise atomic dance. They captured the atomic dance by shining a spotlight on the individual molecules. Then they took snapshots of their atoms, revealing each atom’s precise choreography.
Professor Till Jahnke from the Institute for Nuclear Physics at Goethe University Frankfurt and the Max Planck Institute for Nuclear Physics in Heidelberg explains: “The exciting thing about our work is that we were able to see that the atoms don’t just vibrate individually, but that they vibrate in a coupled manner, following fixed patterns. We directly measured this behavior for the first time in individual medium-sized molecules that were also in their lowest energy state. This zero-point motion is a purely quantum mechanical phenomenon that cannot be explained classically.”
Scientists call these motions vibrational modes and not choreography. In small molecules, containing two or three atoms, figuring out the dance patterns is easy. However, with the increase in the number of molecules, there is a whole repertoire of dance moves to follow. For instance, medium-sized molecule iodopyridine, containing eleven molecules, had 27 different vibrational modes.
According to Jahnke, their experiment ran long back when they collected data in 2019 during a measurement campaign led by Rebecca Boll at the European XFEL, with a totally different goal. It took the team two years to pinpoint the signs of zero-point motion. The eureka moment came through collaboration with their colleagues from theoretical physics from the Center for Free-Electron Laser Science in Hamburg. Scientists developed a new analysis for data interpretation that elevated the level of the research.
To capture an image of dancing atoms, scientists used a technique known as Coulomb Explosion Imaging. In this method, ultrashort, high-intensity X-ray laser pulses are used to cause a controlled explosion in the molecules. This allows the scientists to generate high-resolution images of their structures. The X-ray pulse knocks out electrons from the molecule, making the atoms positively charged that repel each other and fly apart in a fraction of a trillionth of a second. A special apparatus is then used to measure the position and time of impact of the fragments. This helps in the reconstruction of the original structure of the molecule. Goethe University’s Atomic Physics group had developed a COLTRIMS reaction microscope over the past decades. Dr. Gregor Kastirke built a version tailor-made for the European XFEL during his PhD work.
The results shed new light on the world of quantum phenomena. This is the first time researchers have directly observed the complex patterns of zero-point motion in more complex molecules. According to Jahnke, the next step is to record the dance of electrons, which are faster and affected by atomic motion.
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