Physicists at the Massachusetts Institute of Technology (MIT) in the United States have directly observed a "quantum tornado" crystal formed from ultracold atoms.
The research paper was published Jan. 5 in the journal Nature.
It is reported that the world that people perceive is something that classical physics can explain. Where people are, how they move, and how fast they move are determined and unique.
But in the microscopic quantum world, the position of the particles is a matter of probability. For example, an atom has a certain probability of appearing in one position at the same time, and there is also a certain probability of appearing in another position, and the same atom can appear in two or even more places at the same time.
When particles interact purely as a result of quantum effects, a series of strange phenomena follow. But observing this purely quantum-mechanical behavior of particle interactions in a macroscopic world dominated by classical physics is a daunting task.
Physicists at MIT have found that interactions in specific states of matter and quantum mechanics produce a spin quantum fluid composed of ultracold atoms. The researchers predict that in a rotating fluid, the interaction will dominate and drive particles to exhibit strange, never-before-seen behavior.
In this study, the team rapidly rotated a quantum fluid made up of ultracold atoms. They observed that the initial round atomic cloud first turned into an elongated needle-like structure. Then, when classical effects are suppressed, allowing interactions and quantum laws to dominate the behavior of atoms, the needle-like structure spontaneously forms a crystal pattern, like a string of miniature "quantum tornadoes."
The origin of the study
In the 1980s, physicists began observing a new family of matter known as quantum Hall liquids, which consist of clouds of electrons floating in a magnetic field. Instead of repulsive to each other and form crystals as predicted by classical physics, these particles adjust their behavior in a relevant quantum way, based on the behavior of the particles around them.
"People have found all sorts of amazing properties because in a magnetic field, electrons are (usually) frozen in place — all their kinetic energy is turned off, leaving only pure interaction." Richard Fletcher, an assistant professor of physics at the Massachusetts Institute of Technology, said.
Especially in the magnetic field, the movement of electrons is very small and difficult to observe. Martin Zwierlein, a professor of physics at the Massachusetts Institute of Technology, and his colleagues reasoned that since the motion of atoms under rotation occurs at greater distances and scales, using ultracold atoms as stand-ins for electrons could observe the same physical phenomena. "We wanted to make these cold atoms behave like electrons in a magnetic field, but with precise control over them." Then we can imagine what individual atoms are doing and see if they follow the same principles of quantum mechanics. ”
Results already available
First, the team captured about 1 million sodium atoms with a laser and cooled the atoms to a temperature of about 100 nakelvins. An electromagnet system is then used to create a trap to limit the atoms and collectively rotate the atoms at a speed of about 100 revolutions per second like marbles in a bowl.
The team filmed this circular cloud of atoms with a camera, capturing a similar perspective to a child facing the center above a playground carousel. After about 100 milliseconds, the researchers observed the atoms spinning into a long needle-like structure that reached a critical quantum thickness.
"In traditional fluids, like cigarette smoke, it keeps thinning. But in the quantum world, the thickness of fluids reaches its limits. Zverle Rein said. He and his teaching assistant Fletcher published the results of the research up to this stage in a previous paper in the journal Science.
"When we see it reach that limit, we have every reason to think that we're knocking on the door on interesting quantum physics." Fletcher said, "The next question is, what happens to this needle-like fluid under the influence of pure rotation and interaction?"
A "quantum tornado" appears
In a new paper published Jan. 5, the team took their experiment a key step forward to see how the needle-like fluid evolved. They observed that quantum instability came into play: the needle-like structure began to falter, then spiraled, and finally exploded into a string of swirling spots, like a miniature tornado —a quantum crystal formed by the interaction of pure gas rotation, and the interaction between atoms.
"This evolution is related to the butterfly effect, as instability triggers turbulence. Here we have quantum weather: the fluid splits into smaller clouds and swirling crystal structures simply because of its quantum instability. Being able to see these quantum effects directly is a breakthrough. "The Coriolis effect, which explains the effect of the Earth's rotation, is similar to the Lorentz force that explains the behavior of charged particles in a magnetic field." Even in classical physics, this produces interesting patterns, like clouds orbiting the earth in a beautiful spiral motion. Now we can study this phenomenon in the quantum world. ”
"This crystallization process is purely driven by interactions, and it tells us that we are moving from the classical world into the quantum world." Fletcher said.
The results of this study are the first direct and in situ records of the evolution of rapidly rotating quantum gases. Co-authors of the study, including Biswaroop Mukherjee, Airlia Shaffer, Parth B. Patel, Zhenjie Yan, Cedric Wilson and Valentin Crépel, are affiliated with the MIT-Harvard Ultracool Atomic Center and the MIT Electronics Research Laboratory.