Here, here and there
The world we experience is governed by classical physics. Classical physics assumes that we can only exist in one place at any given moment, a premise that determines where we are, as well as how and how fast we move.
In the quantum world, however, microscopic particles are governed by strange quantum physics, and when they interact, they can exhibit a series of strange phenomena. For example, particles can be in different positions at the same time, they can cross what should be insurmountable obstacles, and they can even instantly cross huge distances to share information with other particles.
However, it is very tricky to observe these fragile interactions in the classical world. One way to amplify quantum effects is to cool particles to temperatures close to absolute zero, creating a state of matter called Bose-Einstein condensation that exhibits quantum properties on a larger, visible scale.
Recently, a new study published in the journal Nature shows that physicists used this method to document the key transition of atoms from classical to quantum behavior.
Quantum Hall fluids
The new paper examines a state of matter known as a quantum Hall fluid. In the 1980s, physicists began studying them. This particular state of matter is made up of clouds of electrons floating in a magnetic field, in which electrons do not repel each other and form crystals, as classical physics predicts, but interact in an unusual way—they adjust their behavior to the behavior of neighboring electrons, producing quantum effects.
In a magnetic field, such a fluid can exhibit a wide variety of surprising properties. The reason is that these electrons are "frozen" in the magnetic field, and all their kinetic energy is "turned off", leaving only pure interaction. Thus, such a strange world emerged. However, such phenomena are difficult to observe and understand because in a magnetic field, the movement of electrons is too small.
In the new study, the team thought that the movement of atoms under rotation occurs on a larger length scale than electrons, so they speculated that if ultracold atoms were replaced by ultracold atoms, so that they behave like electrons in a magnetic field, and they were precisely controlled, it might be possible to observe whether atoms also follow the same quantum physics.
A spin fluid composed of ultracold atoms
In the experiment, the research team made a spin fluid composed of ultracold atoms. They captured about 1 million sodium atoms with lasers and cooled them to a temperature of about 100 nanokelvin (nK). They then used a system of electromagnets to create a trap that could limit atoms, placed a cloud of atoms in this electromagnetic trap, and then collectively and rapidly rotated the atoms at a rate of about 100 revolutions per second.
Just like the formation of weather patterns on Earth, a rotating fluid of quantum particles forms a crystal formed by a swirling, tornado-like structure. | Photo credit: Zwierlein et al. / MIT News
They observed that after about 100 milliseconds, the initially circular cloud of atoms began to form an elongated needle-like structure. The rotation continued, and the needle-like structure curved back and forth like a writhing snake and became thinner and thinner. When its thickness reaches a critical value, classical effects are suppressed, leaving only interactions and quantum effects dominating quantum behavior. At this time, the needle-like structure will spontaneously break and break into discrete parts. These discrete parts form a strange crystallization pattern that the researchers describe as a string of tiny quantum tornadoes.
This crystallization process is driven entirely by the interactions between atoms, and it heralds our entry from the classical world into the quantum world. Because in classical fluids, such as cigarette smoke, it will only continue to thin, not reach a limit; but in the quantum world, the thickness of the fluid can reach a critical limit. When this limit is observed, it indicates that the researchers observed the evolution of needle-like fluids under the influence of pure rotation and interaction.
A breakthrough in quantum effects
This is the first direct, in situ record of the evolution of rapidly rotating quantum gases. In fact, the evolution of spin atoms is roughly similar to the large-scale weather patterns caused by the rotation of the Earth. In Earth science, the Coriolis effect, which explains the earth's rotation effect, is similar to the Lorentz force that explains the behavior of charged particles in a magnetic field in physics. Even in classical physics, there are such interesting patterns that form, such as clouds spiraling around the Earth.
Now, new research allows us to observe this phenomenon in the quantum world, where researchers observe the quantum instability exhibited by fluids and ultimately form a crystallization pattern like a miniature quantum tornado. This evolution reminds researchers of the butterfly effect, which is also a turbulence caused by instability. In the new study, this corresponds to "quantum weather": fragments of fluids that have just become quantumly unstable become crystalline structures of smaller "clouds" and "whirlpools". Being able to directly observe these quantum effects is a breakthrough.
#创作团队:
Compilation: Light rain
Typography: Wenwen
#参考来源:
https://news.mit.edu/2022/ultracold-atoms-quantum-0105
https://newatlas.com/physics/quantum-tornadoes-mit/
#图片来源:
Cover image: DWilliam/Pixabay
首图:Zwierlein et al. / MIT News
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