Physicist who took over where Einstein left off

Carl Wieman will present three lectures in Auckland next week.

What could the matter be? That was a question to be taken literally in June 1995 when Carl Wieman and his colleagues, after creating the coldest spot in the universe, created a new form of matter.

The experiment - to bring something weird called Bose-Einstein condensate out of the cold - had worked, but the group of doubting physicists didn't believe what they saw.

"The reaction was one of grave scepticism," says Wieman, who arrives here this weekend to give a series of lectures as part of the World Year of Physics 2005.

"We were hoping to see the shadow but, to be honest, we were hoping to see a much less-pronounced shadow. Experiments that seem too good to be true almost always are."

The strange shadow Wieman and colleague Eric Cornell didn't yet accept was true was cast by a cloud of rubidium atoms cooled to the unimaginable temperature of 100 billionths of a degree above absolute zero (-273.15C).

As Wieman and Cornell found, when it gets that cold, atoms huddle together, lose their identity and fuse into a kind of super atom - "a giant quantum wave" that in a human scale never gets any bigger than the width of a human hair. Who knew?

Actually, Albert Einstein and physicist Satyendra Nath Bose predicted in 1924 something odd like this might happen at temperatures way beyond freezing. But although Einstein and Bose had the theory, they lacked the means to make things really cold.

Even so, the new matter Wieman formed - neither gas, liquid nor solid - is named after them. Einstein is also at the centre of World Year of Physics, which commemorates his pioneering work in 1905, when he wrote papers paving the way for the fields of quantum theory, Brownian motion and relativity.

What convinced Wieman and his group that their results were real was the shape of the atom cloud - an oblate spheroid that was "kind of like a rugby ball" condensing out of the cold.

Wieman and Cornell got over their scepticism, won the 2001 Nobel prize in physics and have seen cold atom laboratories spread around the world. New Zealand has one at Otago University, which collaborates on research with Wieman's lab at the University of Colorado.

Wieman likes to cheerfully call his lab the coldest spot in the universe to illustrate just how darned cold it needs to be for Bose-Einstein condensate. "It can never occur naturally because nature is way too hot," says Wieman. "Nature" in this case means the outer reaches of the universe, where temperatures don't get any colder than 2.7 degrees above absolute zero - "roughly 10 million times too hot for Bose condensate".

The trick to making atoms extremely cold is to corral them in a vacuum intersected by a series of criss-crossing lasers. A whiff of rubidium gas is introduced into the laser field which cools the atoms.

Yes, agrees Wieman, it is counter-intuitive. The energy in light is normally absorbed. For most of us that means when you go out into the sun, you get hot.

A physicist sees things differently. "In that light you absorb all that energy and it turns into making atoms vibrate around and that's heat." But with the right coloured laser light and with the right atoms, it is possible to make sure the energy is never absorbed, but reflects instead.

"It's kind of like having a bowling ball and you're shooting table tennis balls at it. Each time a ball bounces off it gives just a little kick." Which is what the photons of laser light do to the rubidium atoms - slowing down their normal vibrating movements until they feel like they're trapped in treacle.

But the optical molasses trap is still not cold enough to make atoms undergo their transformation. The lasers are switched off and "a rather fancy shape of magnetic field" is applied to hold the atoms.

"It's like a magnetic bowl. The atoms are like little ball bearings rolling around in a bowl," Wieman explains.

By adjusting the shape of the bowl, it is possible to let the most energetic atoms jump out in much the same way as steam evaporates from a cup of tea. Get the bowl shape right and just enough really cold atoms are left behind to form into the condensate.

Great, but what's it for? So far, no one has found any application for this strange new material, mainly because it is so delicate and hard to make.

Plus, it comes in minute amounts. "We talk about it in terms of the number of atoms as opposed to the number of grams. That really means that it's primarily a research tool for understanding quantum physics better."

But because the atoms in the condensate do the same thing, the potential is there to get much better control of atoms, which may be useful in precision instruments, such as atomic clocks. His patient explanations demonstrate that Wieman's other passion is better ways of teaching physics.

"Using the tools of science to teach science" is the theme of one of three Sir Douglas Robb lectures Wieman will give at Auckland University next week. He says the big problem with physics education is the way it is taught through abstract concepts about underlying physical laws.

His research has found a big disconnection between what the experts think they are teaching and what students are learning. He found students memorise and apply equations so they can pass exams, but with no understanding of the concepts involved.

Instead of starting with abstract concepts, Wieman starts with things that are in the real world - such as radios and microwaves when he teaches about electromagnetic waves.

As well as employing a range of teaching tools, Wieman equips students with "personal electronic response systems", like a TV remote control, to answer questions during the session. Results projected on to a screen show how many are getting the answers right.

Wieman disagrees that physics will always be the realm of the few. "It's not that we see the world in a fundamentally different way or have a fundamentally different intuition, we just understand how things apply and how the intuition applies in a different way."

His research involves manipulating the magnetic fields holding the condensate. "We can convert the atoms into sort of exotic giant molecules and put them into quantum super positions where it is half molecule and half atom and do these strange things."

Wieman is now in another world, the world of Feshbach resonance, a place he admits one atomic physicist in 10 and maybe two physicists in 100 will understand what it means. But such is his enthusiasm, there's no doubt that given time, he could explain almost everything that is going on in this tiny cold universe.