Posted on 03/25/2002 6:10:45 PM PST by Texaggie79
Scientists have created a new kind of matter: It comes in waves and bridges the gap between the everyday world of humans and the micro-domain of quantum physics.
Bose-Einstein condensates ("BECs" for short) aren't like solids, liquids and gases. They are not vaporous, hard nor fluid.
There are no ordinary words to describe them. Bose-Einstein condensates are curious objects that obey the laws of the small even as they intrude on the big. BECs come from another world, the world of quantum mechanics.
Quantum mechanics describes the rules of light and matter on atomic scales. Matter can be in two places at once. Objects behave as both particles and waves, a duality described by Schrodinger's wave equation.
Above image: Nobel prizing-winning scientists used lasers and magnetic fields to create a new form of matter. [learn more] Image © 2002 The Nobel Foundation.
BECs come in waves and bridge the gap between the everyday world of humans and the micro-domain of quantum mechanics.
"To see something which nobody else has seen before is thrilling and deeply satisfying. Those are the moments when you want to be a scientist," says Wolfgang Ketterle, at MIT.
BEC is a group of a few million atoms that merge to make a single matter-wave about a millimeter or so across. In 1995, Ketterle created BECs in his lab by cooling a gas made of sodium atoms to a few hundred billionths of a degree above absolute zero, more than a million times cooler than interstellar space.
Right image: BECs form when the atoms in a gas undergo a transition from behaving like the "flying billiard balls" of classical physics to behaving as one giant matter-wave. Image courtesy MIT.
At such low temperatures the atoms become more like waves than particles. Held together by laser beams and magnetic traps, the atoms overlapped and formed a single giant, by atomic standards, matter wave.
Ketterle says "Pictures of BECs can be regarded as photographs of wave functions," or solutions to Schrodinger's equation.
Working independently in 1995, Eric Cornell and Carl Wieman also created BECs. Their BECs were made of super-cold rubidium atoms. Cornell and Wieman shared the 2001 Nobel Prize with Ketterle "for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates."
BECs were predicted by Indian physicist Satyendra Nath Bose and Albert Einstein in the 1920's with the advent of quantum mechanics. Einstein wondered if BECs might too strange to be real, although he could imagine them.
BECs are real and Einstein was right. They are strange.
Ketterle noticed if you create two BECs and put them together, they don't mix like an ordinary gas or bounce apart like two solids might. Where the two BECs overlap, they "interfere" like waves. Thin, parallel layers of matter are separated by thin layers of empty space.
Left image: A picture of overlapping Bose-Einstein condensates. These shadows reveal an "interference pattern" -- a tell-tale sign of wave behavior. Image courtesy MIT.
The pattern forms because the two waves add wherever their crests coincide and cancel where a crest meets a trough. The effect is reminiscent of overlapping waves from two stones thrown into a pond.
"That means ... we have the remarkable effect that an atom (in one BEC) plus an atom (in another BEC) gives no atom. It's a destructive interference," says Ketterle. "Of course we didn't destroy matter; it just appeared somewhere else in the pattern, so the total number of atoms is conserved."
Not all atoms can form Bose-Einstein condensates. "Only those that contain even numbers of neutrons plus protons plus electrons can," says Ketterle. Ketterle made his BECs from sodium atoms. If you add the number of neutrons, protons and electrons in an ordinary sodium atom, the answer is 34, which is an even number. Atoms or isotopes of atoms with odd sums can't form BECs.
One of the most extraordinary aspects of Bose-Einstein condensates is that they are quantum creatures big enough to see. There lies much of their promise. Many of today's cutting-edge technologies; smaller, faster computer chips or micro-electro-mechanical systems (MEMS) or quantum computers lie in a twilight zone between the quantum world and the macroscopic world. Scientists hope that studying BECs will advance those technologies and create others.
Ketterle is already experimenting with one: a pulsed atom-laser.
Right image: Atom-laser pulses produced in Ketterle's lab. The curved shape of the pulses was caused by gravity and forces between the atoms. Click image to enlarge.
"In an ordinary gas, atoms move around randomly. They flit around in all directions. But, in a BEC, all the atoms march lock-step," Ketterle explains. "They are just one single matter-wave propagating in one direction."
Atom-lasers are akin to light-lasers, which are beams of photons that likewise march lock-step. However, there are differences between the two lasers. Atom-laser beams have mass so they will bend downward in Earth's gravitational field.
Light-laser beams lack mass. They bend, too, but the effect is very small. Light-lasers pass through air with ease. Atom-laser beams will be substantially scattered by air molecules.
"Atom lasers need a vacuum to retain their properties," notes Ketterle. They won't be used in the same way as light-lasers. They won't improve CD players or supermarket scanners, for instance. But atom-lasers will doubtless find uses of their own. Ketterle cites atom-lasers possibly being used in "better atomic clocks, which will improve spacecraft navigation." He also thinks atom-lasers will prove useful in atomic optics or very fine lithography.
Who knows where BECs will lead? Humans are still finding innovative uses solids, liquids and gases. Now we get to play with Bose-Einstein condensates.
Source: NASA
Cool! How do you get temperatures that low? I know about using a mixture of Helium-3 and Helium-4, but it sounds like they're using a different technique here.
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Thanks! I didn't know that.
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