News Feature | September 26, 2016

Zapping Schrödinger's Cat With X-Ray Lasers To View Detailed Atomic Motion

By Jof Enriquez
Follow me on Twitter @jofenriq

schroedinger
Zap iodine molecules with laser light and they will split into two quantum “cat states.” Image courtesy of SLAC National Accelerator Laboratory.

Physicists at the Stanford PULSE Institute and the Department of Energy’s SLAC National Accelerator Laboratory have created the world’s most detailed X-ray movie of quantum motion inside a molecule. Their experiment could lead to further understanding of basic functions in living things, such as photosynthesis or vision.

Their method exploits the paradox of Schrödinger’s cat, wherein, similar to a "quantum cat" that is both dead or alive simultaneously, atomic particles can exist in two different physical states at once. Several research groups, including one at the National Institute of Standards and Technology (NIST), have successfully created these quantum cats in separate efforts.

But, the Stanford researchers are the first to exploit this curiosity in the quantum world to view X-ray movies of atomic motion in unprecedented detail.

"This x-ray interference has not been employed to image internal motion in molecules before," they write in the study paper published online in arXiv.org, and accepted for publication in Physical Review Letters.

For this new experiment, the Stanford scientists zapped a two-atom molecule of iodine with an optical green laser, splitting the molecule into two simultaneous states: one excited and the other not. The team then followed up with a second burst of X-ray laser light, which scattered off both versions of the molecule, which later recombined to form an X-ray hologram of concentric rings. After "some clever processing", the scientists were able to string those snapshots of the molecule at different moments in time together to create a stop-motion movie, reports Gizmodo.

“Our movie, which is based on images from billions of iodine gas molecules, shows all the possible ways the iodine molecule behaves when it’s excited with this amount of energy,” said Phil Bucksbaum, a professor at SLAC and Stanford University and director of PULSE, in a news release.

“We see it start to vibrate, with the two atoms veering toward and away from each other like they were joined by a spring. At the same time, we see the bond between the atoms break, and the atoms fly off into the void. Simultaneously we see them still connected, but hanging out for a while at some distance from each other before moving back in. As time goes on, we see the vibrations die down until the molecule is at rest again. All these possible outcomes happen within a few trillionths of a second,” added Bucksbaum.

Zooming in on these atomic vibrations, the scientists were able to observe the molecule's behavior as small as .3 angstrom ­– less than the width of an atom – and as brief as 30 millionths of a billionth of a second, a timescale that captures the vibrations of atoms and molecules.

Exploiting the Schrodinger’s cat paradox, and utilizing intense, ultrashort pulses of coherent light from SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, were key to demonstrating this new method of producing sharp images of intramolecular quantum motion.

“Our method is fundamental to quantum mechanics, so we are eager to try it on other small molecular systems, including systems involved in vision, photosynthesis, protecting DNA from UV damage and other important functions in living things,” said Bucksbaum.