(ORDO NEWS) — The year 2020 will be remembered by the world not only as the year that broke all imaginable and inconceivable temperature records, but also as a period of human history, during which the existence of the third kingdom of particles called “anions”, which exist in two dimensions simultaneously, was proved. In general, speaking about particle physics, it should be noted that until recently there were only two categories or kingdoms – bosons and fermions. The criterion for dividing elementary particles into two camps is the value of the spin, the quantum number, which characterizes the proper angular momentum of the particle. In other words, if the spin of a single particle is determined by an integer, you have a boson in front of you, and if a half-integer, a fermion. This year, researchers discovered the first signs of the existence of a third kingdom of particles – anions, the behavior of which does not resemble the behavior of any bosons. no fermions. We will tell you what anions are and why their discovery is of great importance for modern physics.
What are “anions”?
Every last particle in the universe – from cosmic rays to quarks – is either a fermion or a boson. These categories divide the building blocks of the universe into two different kingdoms. In the outgoing 2020, researchers have discovered the first signs of the existence of a third kingdom of particles – anions. Interestingly, anions do not behave like fermions or bosons; instead, their behavior falls somewhere in between.
In an article published in the summer of 2020 in the journal Science, physicists discovered the first experimental evidence that these particles do not fit into any of the kingdoms known to physicists. “We used to have bosons and fermions, but now we have this third particle kingdom,” said Frank Wilczek, the Nobel Prize winner in physics at MIT, in an interview with Quanta Magazine.
Since the laws of quantum mechanics that describe the behavior of elementary particles are very different from the known laws of classical physics, it is rather difficult to understand them. To do this, the researchers propose to imagine … a pattern of loops. This is because when the anions are entwined, one of them, as it were, “wraps around” the other, changing quantum states.
So, imagine two indistinguishable particles that look like electrons. Take one, and then wrap it around the other so that it returns to where it started from. At first glance, it may seem that nothing has changed. Indeed, in the mathematical language of quantum mechanics, the two wave functions describing the initial and final states must either be equal or have a deviation of one unit. (In quantum mechanics, you calculate the probability of what you observe by squaring the wave function, so that coefficient – 1 – is washed out.)
If the wave functions of the particle are identical, then you have bosons. And if they deviate by 1 factor, then you are looking at fermions. And while the new study’s conclusion may seem like a purely mathematical exercise, it has serious implications for modern physics.
Three kingdoms of elementary particles
The researchers also note that fermions are antisocial members of the particle world, as they never occupy the same quantum state. Because of this, electrons, which belong to the class of fermions, fall into various atomic shells around the atom itself. From this simple phenomenon arises most of the space in the atom – the amazing variety of the periodic table and all of chemistry.
Bosons, on the other hand, are herd particles with the happy ability to combine and share the same quantum state. Thus, photons, which are classified as bosons, can pass through each other, allowing light rays to travel unhindered rather than scatter.
But what happens if you loop one quantum particle around another? Will it return to its original quantum state? To understand whether this will happen or not, you need to delve into a short course in topology – the mathematical study of shapes. It is considered that two forms are topologically equivalent if one can be transformed into another without any additional actions (gluing or splitting). A donut and a coffee mug, as the old saying goes, are topologically equivalent because one can be smoothly and continuously shaped into the other.
Consider the loop we made when we rotated one particle around another. In three dimensions, this loop can be compressed to a point. Topologically, it looks as if the particle did not move at all. However, in two dimensions, the loop cannot collapse; it gets stuck on another particle. This means that you cannot compress the loop in the process. Because of this limitation – found in only two dimensions – the loop of one particle around another is not equivalent to the particle being in the same place. Yes, my head is spinning. This is why physicists needed a third class of particles – anions. Their wave functions are not limited to the two solutions that define fermions and bosons, and these particles are neither.
“The topological argument was the first sign of the existence of anions,” says one of the authors of the scientific work Gwendal Feve, a physicist at the Sorbonne University in Paris. When electrons are constrained in motion in two dimensions, they cool to near absolute zero when exposed to a strong magnetic field.
In the early 1980s, physicists first used these conditions to observe the “fractional quantum Hall effect,” in which electrons come together to create so-called quasiparticles, which have a fraction of the charge of one electron. In 1984, a groundbreaking two-page paper by Frank Wilczek, Daniel Arovas, and John Robert Schrieffer showed that these quasiparticles could be anything. But scientists have never observed such a behavior of quasiparticles, which means they could not prove that anions are not like either fermions or bosons.
That’s why the new research is revolutionary – physics has finally succeeded in proving that anions behave like a cross between the behavior of bosons and fermions. Interestingly, in 2016, three physicists described an experimental setup that resembles a tiny hadron collider in two dimensions. Fev and his colleagues built something similar to measure current fluctuations in the collider.
They were able to show that the behavior of the anions exactly corresponds to the theoretical predictions. In general, the authors of the scientific work hope that entangled anions can play an important role in the creation of quantum computers.
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