Now comes a report of a quantum gas, called a Bose-Einstein condensate, that scientists at the Massachusetts Institute of Technology first stretched into a thin rod and then spun until it broke. The result was a series of daughter vortices, each a mini-me of the parent form.
Spinning quantum clouds, effectively quantum tornadoes, are reminiscent of phenomena seen in the large-scale classical world we know. An example would be what is called Kelvin-Helmholtz clouds, which look like periodic repeating jagged cartoon images of ocean waves.
These wave-like clouds, seen over an apartment complex in Denver, exhibit what is known as Kelvin-Helmholtz instability.Rick Duffy/Wikipedia
The way of doing quantum cloud vortices, however, involve more laboratory equipment and less atmospheric wind shear. “We start with a Bose-Einstein condensate, 1 million sodium atoms that share a single quantum mechanical wave function,”…, says Martin Zwierlein, professor of physics at MIT.
The same mechanism that confines gas, a atom trap, made up of laser beams, allows researchers to squeeze it and then spin it like a propeller. “We know which direction we’re pushing and we see the gas stretching out,” he says. “The same thing would happen to a drop of water if I spun it the same way – the drop would lengthen as it spun.”
What they actually see is actually the shadow cast by the sodium atoms as they fluoresce when illuminated by laser light, a technique known as absorption imaging. Successive frames of a film can be captured by a well-placed CCD camera.
At a particular rotation rate, the gas breaks up into small clouds. “It develops these funny ripples – we call it flaky, then gets even more extreme. We see how this gas ‘crystallizes’ into a chain of droplets – in the last image there are eight droplets.
Why settle for one dimensional crystal when you can opt for two? And in fact, the researchers say they did just that, in as yet unpublished research.
The theory had predicted that a spinning quantum gas would break into drops, i.e. it could be inferred that this would happen from previous theoretical work. “We in the lab weren’t expecting this – I wasn’t aware of the paper; we just found it,” says Zwierlein. “It took us a while to figure it out.”
The crystalline form appears clearly in a magnified portion of one of the images. Two connections, or bridges, can be seen in the quantum fluid, and instead of the single large hole you would see in water, the quantum fluid has a whole train of quantized vortices. In a zoomed-in portion of the image, the MIT researchers found a number of these small, hole-like patterns, strung together in a regularly repeating fashion.
“It’s similar in what happens when clouds cross in the sky,” he says. “An originally homogeneous cloud begins to form successive fingers in the Kelvin–Helmholtz diagram.”
Very pretty, you say, but surely there can be no practical application. Of course it can; the universe is quantum. The research at MIT is funded by DARPA, the Defense Research Advanced Project Agency, which hopes to use a ring of quantum tornadoes as fabulously sensitive rotational sensors.
Today, if you are a submarine lying under the sea, in secrecy, you might want to use a fiber optic gyroscope to detect slight rotational motion. Light travels back and forth in the fiber, and if everything spins, you should get an interference pattern. But if you use atoms instead of light, you should be able to do the job better, because atoms are much slower. Such a quantum tornado sensor could also measure slight changes in Earth’s rotation, perhaps to see how the Earth’s core might affect things.
The MIT researchers got deep down the rabbit hole, but not quite deep. These smaller daughter tornadoes can be confirmed to still be Bose-Einstein condensates, as even the smaller ones still have about 10 atoms each. If you could get down to just one per vortex, you’d have the quantum hall effect, which is a different state of matter. And with two atoms per vortex, you would get a “Fractional quantum hall“Fluid, with each atom ‘doing its own thing, not sharing a wave function,’ says Zwierlein.
Quantum Hall effect is now used for define report Planck’s constant divided by the charge of the squared electron (h/e2)—a number called the von Klitzing constant– which is about as basic as basic physics. But this effect is not yet fully understood. Most studies have focused on the behavior of electrons, and MIT researchers are trying to use sodium atoms as surrogates, Zwierlein says.
So while they’re not all the way down the ladder yet, there’s plenty of room for discovery on the way down. Like Feynman also could have said (kind of).
From articles on your site
Related articles on the web