Now comes a report on a quantum gas, called a Bose-Einstein condensate, which scientists at the Massachusetts Institute of Technology first stretched into a skinny rod, then rotated until it broke up. The result was a series of daughter vortices, each one a mini-me of the mother form.
The research, published in Nature, was conducted by a team of scientists affiliated with the MIT-Harvard Center for Ultracold Atoms and MITs Research Laboratory of Electronics.
The rotating quantum clouds, effectively quantum tornadoes, recall phenomena seen in the large-scale, classical world that we are familiar with. One example would be so-called Kelvin-Helmholtz clouds, which look like periodically repeating, serrated cartoon images of waves on the ocean.
These wave-shaped clouds, seen over an apartment complex in Denver, exhibit whats called Kelvin-Helmholtz instability.Rick Duffy/Wikipedia
The way to make quantum cloud vortices, though, involves more lab equipment and less atmospheric wind shear. We start with a Bose-Einstein condensate, 1 million sodium atoms that share one and the same quantum-mechanical wave function,, says Martin Zwierlein, a professor of physics at MIT.
The same mechanism that confines the gasan atom trap, made up of laser beamsallows the researchers to squeeze it and then spin it like a propeller. We know what direction were pushing, and we see the gas getting longer, he says. The same thing would happen to a drop of water if I were to spin it up in the same waythe drop would elongate while spinning.
What they actually see is effectively the shadow cast by the sodium atoms as they fluoresce when illuminated by laser light, a technique known as absorption imaging. Successive frames in a movie can be captured by a well-placed CCD camera.
At a particular rotation rate, the gas breaks up into little clouds. It develops these funny undulationswe call it flaky, then becomes even more extreme. We see how this gas crystalizes in a chain of dropletsin the last image there are eight droplets.
Why settle for a one-dimensional crystal when you can go for two? And in fact the researchers say they have done just that, in as yet unpublished research.
That a rotating quantum gas would break into blobs had been predicted by theorythat is, one could infer that this would happen from earlier theoretical work. We in the lab didnt expect thisI was not aware of the paper; we just found it, Zwierlein says. It took us a while to figure it out.
The crystalline form appears clearly in a magnified part of one of the images. Two connections, or bridges, can be seen in the quantum fluid, and instead of the single big hole youd see in water, the quantum fluid has a whole train of quantized vortices. In a magnified part of the image, the MIT researchers found a number of these little holelike patterns, chained together in regularly repeating fashion.
Its similar in what happens when clouds pass each other in the sky, he says. An originally homogeneous cloud starts forming successive fingers in the Kelvin-Helmholtz pattern.
Very pretty, you say, but surely there can be no practical application. Of course there can; the universe is quantum. The research at MIT is funded by DARPAthe Defense Research Advanced Project Agencywhich hopes to use a ring of quantum tornadoes as fabulously sensitive rotation sensors.
Today if youre a submarine lying under the sea, incommunicado, you might want to use a fiber optic gyroscope to detect slight rotational movement. Light travels in both one way and the other in the fiber, and if the entire thing is spinning, you should get an interference pattern. But if you use atoms rather than light, you should be able to do the job better, because atoms are so much slower. Such a quantum-tornado sensor could also measure slight changes in the earths rotation, perhaps to see how the core of the earth might be affecting things.
The MIT researchers have gone far down the rabbit hole, but not quite to the bottom of it. Those little daughter tornadoes can be confirmed as still being Bose-Einstein condensates because even the smallest ones still have about 10 atoms apiece. If you could get down to just one per vortex, youd have the quantum Hall effect, which is a different state of matter. And with two atoms per vortex, youd get a fractional quantum Hall fluid, with each atom doing its own thing, not sharing a wave function, Zwierlein says.
The quantum Hall effect is now used to define the ratio of Plancks constant divided by the charge of the electron squared (h/e2)a number called the von Klitzing constantwhich is about as basic as basic physics gets. But this effect is still not fully understood. Most studies have focused on the behavior of electrons, and the MIT researchers are trying to use sodium atoms as stand-ins, says Zwierlein.
So although theyre not all the way to the bottom of the scale yet, theres plenty of room for discovery on the way to the bottom. As Feynman also might have said (sort of).
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