Schrödinger’s Cat is probably the most famous quantum mechanical idea, but the science behind it can also be used in actual experiments, such as filming the detailed behavior of molecules.

Scientists from the SLAC National Accelerator Laboratory have put iodine molecules in two states at once, excited and unexcited – dubbed a "cat state" – and used X-rays from the Linac Coherent Light Source (LCLS) to study how the molecules behave. By collecting data from billions of molecules, the researchers were able to create a movie of what happens in the quantum world.

The LCLS is the most powerful X-ray laser in the world, allowing researchers to produce observations with a huge amount of information. The scientists can see details as small as 0.03 nanometers (about the size of the helium atom) and changes as brief as 30 millionths of a billionth of a second.

“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 senior author Phil Bucksbaum, a professor at SLAC, in a statement.

In this research, available on arXiv and accepted for publication in Physical Review Letters, the team looked at the vibrating molecules made of two iodine atoms. The molecules were put in a cat state where, just like in the famous thought experiment, they were in two different configurations at once: excited and unexcited.

The researchers shot X-rays at them and the powerful photons hit both configurations at the same time, creating an X-ray hologram that was a detailed image of the molecule's excited state. This approach allowed scientist to “see” what’s happening at an atomic level.

“We see it start to vibrate, with the two atoms veering toward and away from each other like they were joined by a spring,” Bucksbaum explained. “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.”

Schrödinger’s Cat is a famous paradox thought up by Austrian physicist Erwin Schrödinger to challenge the way quantum mechanics could be linked to the macroscopic world. Over time, the experiment has become a household example for particles in superposition, when they are in two states at the same time, like the famous cat that was thought to be both alive and dead.

^{In this short animation, the red dots represent the molecules in an unexcited state and the blue are the molecules in an excited state. The excited state ones vibrate more vigorously, moving further apart and even breaking free from each other. J.M. Glownia et al./ SLAC}