Selected from IEEE Spectrum
Machine Heart Compilation
Editors: Zhang Qian, Zenan
Is this quantum mechanics? I couldn't understand it but I was shocked.
If you know a little about fluid mechanics, you will know that this field is known for being "difficult", and some of the principles are plausible, unconcerned, and explained in a variety of ways, and the vast majority of people who study this field may find it difficult to obtain significant results.
Physicist Werner Heisenberg once said, "When I meet God, I ask Him two questions: Why is there a theory of relativity?" Why turbulence? I think God may only be able to answer the first question."
40 years ago, physicist Richard Feynman added, "If you think you know quantum mechanics, then you don't understand quantum mechanics." It's a subject that challenges intuition and sometimes leaves even the physicists who study it stunned.
So what would be the result if fluids were studied in the field of quantum mechanics?
A group of MIT researchers did.
In quantum mechanics there is a concept called "Bose-Einstein condensed matter" that can be produced by quantum gases under weightless conditions. Scientists hope to use this ultra-low temperature quantum gas under zero gravity to develop high-precision measuring instruments such as atomic interferometers for measuring the earth's gravitational field.
Recently, a related study from MIT appeared in the journal Nature.
Thesis Link:
In this study, the authors first stretched the "Bose-Einstein condensate" into a slender strip, and then rotated the thin strip until the thin strip ruptured. The result of these operations is a series of sub-vortexes, each of which is a miniature version of the female vortex.
These spinning quantum clouds (quantum tornadoes) are reminiscent of phenomena in the classical world as we're familiar, such as the Kelvin-Helmholtz cloud, which looks like periodic repetitive jagged cartoon waves.
However, the conditions for making quantum cloud vortexes are very demanding, requiring a lot of laboratory equipment and reducing atmospheric wind shear. Martin Zwierlein, a professor of physics at MIT, said, "We start with the Bose-Einstein condensate, where 1 million sodium atoms share the same quantum mechanical wave function."
The same mechanism of confining the gas to an atomic trap composed of a laser beam allows the researchers to squeeze it and then spin it like a propeller. "We know the direction we're pushing, we're seeing the gas getting longer," he said. If I rotate a drop of water in the same way, the same thing happens – the drop of water stretches as it spins."
What they actually saw was the shadow cast by sodium atoms as they fluoresced under laser irradiation, a technique known as absorption imaging.
At a specific rotational speed, the quantum gas splits into small clouds. "It creates some interesting fluctuations — we call flaky — and then it gets more extreme." We see how this gas "crystallizes" in a string of droplets – eight droplets in the last photo.
Since two-dimensional crystals can be obtained, why settle for one-dimensional crystals? In fact, the researchers say they have done this in unpublished studies.
Previous theories have predicted that rotating quantum gases will split into small pieces — that is, one can infer this from early theoretical work.
But Zwierlein said they hadn't noticed the paper before. In most of the retraction of one of the images, the crystal form is clearly visible. In a quantum fluid you can see two connections, or bridges, instead of a large hole we've seen in the water, and the quantum fluid has a whole string of quantized swirls. In most of the images, the MIT researchers found many of these small hole-like patterns, which are linked together in a regular repetitive manner.
"A similar phenomenon occurs when clouds meet each other in the sky," says Zwierlein. "What would have been a homogeneous cloud would begin to form continuous fingers in the Kelvin-Helmholtz pattern."
Seeing this, you might say: Another fancy quantum mechanical study, but it doesn't make much sense, right? The answer is no, the entire universe is quantum-based. The MIT study received a grant from darpa, the Defense Research Advanced Projects Agency, which wants to use a quantum tornado as an extremely sensitive rotational sensor.
If you're navigating a submarine cruising underwater, you may need to use a fiber optic gyroscope to detect slight rotational motion because the water is cut off from communication. Light travels in different ways in the fiber, and if the entire object is rotating, you should get an interference pattern. But if you're using atoms instead of light, you should be able to do the job better because atoms are much slower.
This quantum tornado sensor can also measure small changes in the Earth's rotation, and perhaps we can use it to understand how the Earth's core affects things.
MIT scientists have opened the door to a new world, but not quite. What is currently confirmed is that those tornadoes are still Bose-Einstein condensates, as even the smallest tornadoes still have about 10 atoms each. If there is only one atom per vortex, a quantum Hall effect is created, which is a different state of matter. If each vortex had two atoms, you would get a "fractional quantum Hall" fluid, with each atom "doing its own thing and not sharing wave functions," Zwierlein says.
The quantum Hall effect is now used to define the smallest unit of resistance: the ratio of planck's constant h divided by the square (h/e2) of the electron charge e – a number called von Neumann. Kreetzing constant – this is as basic as fundamental physics.
But this effect is still not fully understood. Zwierlein believes that most research has focused on the behavior of electrons, and that researchers at MIT are trying to use sodium atoms as alternatives.
So, although they have not yet fully reached the smallest scale, there is still a lot of room for discovery in the process of reaching the limit. There's Plenty of Room at the Bottom.
For reference:
https://spectrum.ieee.org/quantum-tornadoes-mit
https://phys.org/news/2022-01-physicists-ultracold-atoms-crystal-quantum.html
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