MIT boffins make hot superfluid

For a specified value of 'hot'

Scientists at MIT have created a new kind of matter: a gas of atoms that exhibits superfluidity at high temperatures. Or at least, what passes for high temperatures among researchers at the MIT Harvard Center for Ultracold atoms.

A superfluid gas flows without resistance, and has some very odd properties. One of these is that it will only rotate when it is punctuated by vortices, similar to miniature tornados, making it easy to distinguish from a normal gas.

The research team spent a year trying to cajole their gas sample into rotating. First, they had to cool their sample to close to absolute zero. This is done by laser and evapourative cooling, which we are willing to bet is easier to type than to do. Next, they had to trap the gas in the focus of an infrared laser beam. The electric and magnetic fields of the beam are what hold the atoms in place.

The last step is to get the gas to rotate by spinning a green laser beam around it, a process graduate student Martin Zwierlein described as being "like sanding the bumps off of a wheel to make it perfectly round".

The team finally spotted the vortices when the gas was cooled to 50 billionths of a degree Kelvin.

Hold on, we hear you ask, didn't they say high temperature superfluidity? Well, yes they did, and we agree that 50 billionths of a degree Kelvin sounds pretty chilly to us.

Fortunately, a Nobel laureate was able to clarify the situation: "It may sound strange to call superfluidity at 50 nanokelvin high-temperature superfluidity, but what matters is the temperature normalized by the density of the particles," said Wolfgang Ketterle, head of the MIT research Group.

Using this rather dodgy sounding logic,( but hey, if you can't trust a Nobel laureate, who can you trust?), it seems the team is allowed to scale their results up from the very high densities of fermionic atoms to the more spaced-out nature of mere solids. Once they do this, the numbers show that the superfluidity happened a really quite high temperatures after all. Higher, even, than room temperature.

Dan Kleppner, director of the MIT-Harvard Center for Ultracold Atoms, said, "This is not a smoking gun for superfluidity. This is a cannon."

The team's work is published in today's (23 June) issue of Nature. ®

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