All particles in the universe can be divided into two categories-fermions or bosons. For example, electrons are typical fermions, and they cannot be in the same state; while photons are typical bosons, the same photons can gather together. Now, scientists have discovered the third type of particles-anyons, which are not completely detached, but the degree of aggregation is much lower than that of bosons.
The reason why this type of particles can be divided into completely new types is that they are neither like fermions nor bosons. They are in an intermediate state. In a paper recently published in the journal Science, physicists obtained experimental evidence for the first time, proving that anyons cannot be classified into the other two particle kingdoms. "We have bosons and fermions, and now we have a third kingdom," said Frank Wilczek of the Massachusetts Institute of Technology, the Nobel Prize winner in physics. "This is definitely a milestone. "
What Is Anyon?
Before getting to know anyons, let's take a look at bosons and fermions. In a system consisting of identical particles, if only one particle is allowed to be accommodated in a quantum state of the system (that is, a microscopic state determined by a set of quantum numbers), this kind of particle is called a fermion. For example, two electrons cannot be in the same state, and electrons are fermions. The boson is the opposite, two identical bosons can be in the same state, and photons are typical of bosons.
Fermions are "solitary people" in the particle world, and they never occupy the same quantum state. Because of this, the electron, which is one of the fermions, is forced into the atomic shell surrounding the atom. This seemingly simple phenomenon has resulted in a lot of space in the atom. As a result, the periodic table of the elements has undergone amazing changes and chemistry was born.
On the other hand, bosons are gregarious particles, willing to gather together to share the same quantum state. So photons that are bosons can pass through each other, allowing light to travel unhindered instead of scattered around.
But what happens if a quantum particle turns around another quantum particle without returning to the same quantum state? In order to understand this possibility, we need to make a brief discussion of topology, the mathematical study of shapes. If one of the two shapes can be transformed into the other without any cutting or bonding, then the two shapes are topologically equivalent. A donut and a coffee cup are similar in abstract shape, so we think they are equivalent in topology.
Now imagine the trajectory of a particle when it revolves around a particle. In three-dimensional space, we can shrink this trajectory until it reaches a certain point. Topologically speaking, it seems that the particles have not moved at all.
However, in a two-dimensional space, this trajectory cannot be contracted. Because this trajectory contains another particle. In this process, the contraction cannot continue without cutting off the track. Because of this limitation of two-dimensional space, rotating a particle around another particle is not the same as leaving the particle in the same position.
Therefore, we believe that there is a third type of particle, the possibility of anyon. Since their wave functions are not limited to the two solutions that define fermions and bosons, these particles do not belong to these two solutions, nor do they belong to anything in between. When Wilczek first coined the term anyon, he was implying that anything could happen.
Verify with Experiment
Gwendal Fève, a physicist at Sorbonne University in Paris, organized this experiment to verify anyons. He said, "The topological argument is the first hint of the existence of anyons, and what we are looking for is the physical system."
When electrons are confined to two-dimensional motion, cooled to close to absolute zero, and subjected to strong magnetic fields, very strange things can happen. In the early 1980s, physicists used these conditions to observe the "fractional quantum Hall effect" for the first time. In this process, electrons gather together to produce so-called quasi-particles whose charge is only a small amount of that of a single electron. section. (If you think it seems strange to call the collective behavior of electrons a particle, then think of the proton, which itself is even made up of three quarks.)
In 1984, a two-page seminal paper by Wilczek, Daniel Arovas, and John Robert Schrieffer showed that these quasiparticles must be randomons. But scientists have never observed anyon-like behavior in these quasiparticles. In other words, they could not prove that any one particle is different from fermions or bosons, that is, they could neither gather together nor completely repel each other.
What the new research wants to do is complete this proof. In 2016, three physicists described an experimental device that resembled a miniature particle collider in two dimensions. Feifee and his colleagues built a similar instrument based on this, and used this instrument to carry out anyon collision experiments. By measuring the current fluctuations in the collider, they were able to prove whether the behavior of anyons was consistent with theoretical predictions.
Using this device, researchers mainly want to observe the results of the collision between two indistinguishable particles. If fermions collide in this device, then these particles will part ways and leave along different paths after the collision; if they collide with bosons, they will come together at the same exit. Appear everywhere.
In the collision experiment, the anyons did not show the above two results. The anyons at the exit were not completely separated, but they were not completely assembled, and the degree of aggregation was much smaller than that of bosons. Therefore, this is also the first experiment to prove the existence of anyon.
Brown University physicist Dmitri Feldman (Dmitri Feldman) did not participate in the recent research, he believes, "There is no doubt that everything is in accordance with the theory. In my experience, this situation is The field is very unusual."
Wilczek said: "For a long time, there has been a lot of evidence pointing to the existence of anyons. But if you ask: 'Is there a phenomenon that can only be caused by anyons?' From different levels,, the answer is very clear. "
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