SLAC National Accelerator Laboratory

Schrödinger's cat behaviour has been filmed in atoms for the first time

An atomic cat state. 

BEC CREW
26 SEP 2016
 

Physicists have filmed atoms entering a Schrödinger’s cat-like state in unprecedented detail, revealing what it looks like when atoms exist in two entirely different states at the exact same time.

The team came up with a technique that allowed them to capture details as small as 0.3 ångström - or less than the width of an atom - and as brief as 30 millionths of a billionth of a second. Those images formed the basis of the first ever stop-motion movie of an atomic 'cat state'. 

 

For those of you who need a quick refresher, here’s a really basic run-down of the Schrödinger’s cat thought experiment. 

Dreamt up by Austrian physicist Erwin Schrödinger in 1935, the Schrödinger’s cat experiment proposes that you (hypothetically) put a cat in a box with some live explosives that have a 50/50 chance of exploding once you close the lid.

For our purposes, this is a magical, explosion-proof box that reveals nothing about what's actually happening on the inside, so until you open the box, you have no idea what state your cat is in. 

That means until you open the box, your cat occupies two states simultaneously - dead or alive (and a secret third option: incredibly pissed).

What's tricky about this hypothetical scenario is that for as long as you keep that box lid closed, your cat is in what's known as a superposition state - it's both dead and alive, because it has to be one, and it can't be neither.

While Schrödinger came up with this experiment to mull over the nature of reality in our Universe, and to demonstrate how weird quantum mechanics actually is, decades later, physicists realised that atoms can perform a real-life version of the cat’s twin states.

 

As Jennifer Ouellette explains for Gizmodo, in 2005, physicists from the US National Institute of Standards and Technology successfully created a 'cat state' in the lab, where six atoms were shown to be in simultaneous 'spin up' and 'spin down' states. 

"Think of it as spinning clockwise and counter-clockwise at the same time," she says.

The principle has gone on to form the very basis of quantum computers - tipped to be the next generation of computing technology that will blow our current computers out of the water - and while physicists have gotten pretty good at forcing atoms into a superposition state, until now, no one’s been able to film the behaviour clearly.

To achieve this, a team from Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory created a two-atom molecule of iodine.

They blasted this molecule with an X-ray laser, causing it to absorb a short burst of energy. This zap prompted the molecule to splits into two versions of itself - one excited, the other not excited. 

cat-stateSLAC National Accelerator Laboratory

When this split molecule was blasted by another burst of X-ray laser, the light particles - or photons - scattered off of both versions of the molecule, and recombined to form an X-ray hologram of the action.

cat-state-2wSLAC National Accelerator Laboratory

The team performed this experiment over and over again, and managed to string together a series of X-ray snapshots to create the world’s most detailed X-ray movie of the inner machinery of a molecule.

"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," says one of the team, Phil Bucksbaum, in a press release.

You can see the results below:

Here’s Bucksbaum explaining what you just watched:

"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."

Not only has the team managed to image the behaviour of an iodine molecule in more detail than ever before, but they say this filming technique can be retroactively applied to data from past experiments.

"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," says Bucksbaum.

The study has been accepted for publication in an upcoming edition of Physical Review Letters, but you can read it now on pre-print website, arXiv.org.

And you really need to watch the team's explainer video of the experiment, because it's glorious:

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