International Space Station

For 18 years Professor Barry Garraway has wondered what might be revealed by his ‘atomic bubble trap’ if it were ever to be created in a place without gravity.

Now the University of Sussex quantum physicist is about to find out. A box containing the equipment for his experiment, which involves cooling atoms to a fraction above absolute zero (minus 273 degs C), was sent by unmanned rocket to the International Space Station (ISS) on 21 May.

Once the equipment is fully operational on board the ISS, NASA astronauts will set the experiment running to see what happens to the cooled atoms in a complete vacuum. Will they behave as Professor Garraway predicts and move in unison to create a wave motion similar to light waves, but inside a bubble of atomic matter? Or will something completely unexpected happen?

The answers, expected later this year, will give insights into some of the fundamental properties of matter and the nature of gravity, and could also unlock the mysteries of dark energy - the bits of the universe we know exist but cannot see.

For Professor Garraway, it will be a proud moment. “I was delighted that my experiment was selected out of thousands that were under consideration. As a theoretical physicist, it’s incredibly exciting to see the moment when experimentalists pick up on your theory and actually do the experiment.”

Professor Garraway developed his bubble trap experiment in 2000 after his colleagues at Sussex were the first physicists in the UK to create a Bose-Einstein Condensate, in which 100,000 atoms were cooled to just a few hundred billionths of a degree above the coldest temperature it is possible to reach.

In this state atoms are virtually motionless and without energy, which causes them to collapse and merge into a ‘superatom’. Although predicted by Saytendra Bose and Albert Einstein in the 1920s, the phenomenon was only proved through experiments in 1995.

Professor Garraway proposed to develop the experiment further by creating a bubble shape with the cooled atoms (of the metal rubidium) to observe what would happen.

He hoped to see the atomic bubble move in unison in a wave motion, but the effect of the Earth’s gravity would cause the atoms to collapse before scientific observations could be completed.

“I knew that gravity was an issue with this,” he says. “But as we didn’t have the option of trying it in space, I put the experiments aside and moved on to other work.”

When NASA put a call out for ISS projects, Nathan Lundblad, an academic who had been adapting Professor Garraway’s experiment, submitted the matter-wave bubble idea. 

After the project was accepted, Professor Garraway visited the Jet Propulsion Laboratory in Pasadena, USA, where the experiment was assembled by NASA engineers and Cold Atom Laboratory (CAL) researchers prior to launch.

“The fact that this is now being followed up by NASA as a space experiment is tremendously exciting as it realises the original vision for the bubble trap,” he says.

“And it has renewed my interest.  I am going to think about different technical aspects of the experiment.  We could get the bubble of atomic matter to collapse and vibrate and make different shapes. Choosing different topologies usually means that something interesting happens.”

The challenge for the NASA astronauts when the experiment is running will be in creating as little disturbance in the ISS as possible.

“It’s a very fragile experiment for what is still quite a hostile environment,” says Professor Garraway. “So the experiment will run during the astronauts’ rest periods and will be controlled remotely from the ground.

"Studying these ultra-cold atoms could inform our development of Quantum Technologies, or even reshape our understanding of matter and the fundamental nature of gravity.”