Physicists have discovered that supercooled atomic clouds can form ‘quantum tornadoes’

Physicists at the Massachusetts Institute of Technology have succeeded in creating a ‘quantum tornado’ in an extremely cold atomic cloud, according to last paper Published in Nature magazine. This is the first direct, In place Documented how rapidly rotating quantum gases evolved, and according to the authors, the process is similar to how the effects of Earth’s rotation can give rise to large-scale weather patterns.

MIT scientists are interested in studying the so-called Quantum Hall Liquid. First discovered in the 1980s, quantum Hall fluids consist of a cloud of electrons floating in a magnetic field. In the classical system, electrons repel each other and form crystals. But in a quantum Hall fluid, electrons mimic the behavior of their neighbors – evidence of quantum correlation.

“People have discovered all kinds of amazing properties, and the reason is that, in a magnetic field, electrons (classically) freeze in place — all their kinetic energy is turned off, and all that’s left is pure interaction.” Co-author Richard Fletcher said:, a physicist at the Massachusetts Institute of Technology. “So, this whole world appeared. But it is very difficult to notice and understand.”

So Fletcher and his colleagues thought they might be able to simulate this unusual electron behavior using a very cold cloud of quantum gas. known as Bose-Einstein Capacitors (BEC)These gases are named in honor of Albert Einstein and the Indian physicist Satyendra Bose. In the 1920s, Bose and Einstein predicted the possibility that the wave nature of atoms would allow propagation and interference if they were sufficiently grouped together.

At normal temperatures, the atoms act like billiard balls and bounce off each other. Lowering the temperature reduces the speed. If the temperature dropped low enough (a millionth of a degree above absolute zero) and the atoms were packed dense enough, the different waves of matter would be able to “feel” each other and coordinate themselves as if they were “big meta-atoms”. “.

The first BEC is Made in 1995Within a few years, more than thirty teams had replicated the experiment. that Nobel laureate’s invention He launched a completely new branch of Physics. BEC Scientist succeeded To study the strange little world of quantum physics as if they were looking at it through a magnifying glass, because BEC “amplifies” atoms in the same way a laser amplifies photons.

Ultracold atomic gases are good at simulating electrons in solids, but they have no charge. This neutrality can make simulated phenomena such as the quantum Hall effect challenging. Implementing such a neutral regime is one way to overcome this obstacle.

“We thought, ‘Let’s make these cold atoms behave as if they were electrons in a magnetic field, but we can control them precisely,'” Co-author Martin Zwierlein said:He is also a physicist at the Massachusetts Institute of Technology. “Then we can visualize what each atom is doing and see if they are subject to the same quantum mechanical physics.”

Using laser traps, the MIT scientists cooled about a million atoms of sodium gas. The cooled atoms are held in place by a magnetic field. The second step is evaporative cooling, in which a network of magnetic fields conspires to repel the hotter atoms so that the colder atoms can move closer to each other. The process works in much the same way as evaporative cooling with a hot cup of coffee: the hottest atoms rise to the top of the magnetic trap and “jump out” as vapour.

This same magnetic field can make the atoms in the trap spin at about 100 revolutions per second. This motion is captured with a CCD camera, thanks to the way the sodium atoms fluoresce in response to the laser beam. The atoms form an image which can then be observed using a technique called absorption imaging.

Within 100 milliseconds, the atoms spin into long, thin, needle-like structures. Unlike conventional liquids (such as cigarette smoke), which make themselves lighter, quantum fluids have a limit on how thin the liquid can become. MIT researchers have discovered that the needle-like structures that form in their ultra-cold gas have reached this point. Researchers described their spin quantum gas and related findings last year in science.

This latest research takes the MIT experience one step further by examining how needle-like fluids evolve under conditions of pure spin and atomic interactions. The result: quantum instability appears, causing the fluid needle to vibrate, and then a switch. Eventually, the liquid crystallizes into a series of rotating clumps that resemble tornadoes – quantum crystals formed entirely from the interaction of atoms in a rotating gas. Its evolution is very similar to the formation called Cloud Kelvin Helmholtzwhere homogeneous clouds begin to form successive radii as a result of differences in speed (velocity and direction) between wind currents in the atmosphere.

“This development has to do with the idea of ​​how a butterfly in China can create a hurricane here, because of the instability that causes the disturbance,” Zwerlin said. “Here, we have quantum weather: liquids, simply from their quantum instability, break down into these crystal structures from smaller clouds and eddies. And it’s a breakthrough to be able to see these quantum effects firsthand.”

Apparently, this behavior was predicted in previous paper by another physicist, which the MIT team recently discovered. There are several potential practical applications of this research, especially rotation sensors which are very sensitive to marine navigation. submarine Depends profession fiber optic gyroscope To detect rotational motion when immersed, generate an alarm interference pattern. Atoms move slower than light, so quantum tornado sensors will be more sensitive—and perhaps sensitive enough to measure subtle changes in Earth’s rotation.

DOI: Nature, 2022. 10.1038 / s41586-021-04170-2 (About DOI).

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