“If you think you understand quantum mechanics, you haven’t understood it.” With this phrase, Nobel Prize winner Richard Feynman, one of the ‘fathers’ of the scientific discipline that has most changed our conception of the world, wanted to underline how complicated it is to understand a reality in which objects can be in several places at once. time, cleanly pass through solid barriers and even communicate instantly over enormous distances. Behaviors that may seem impossible, but that are very present in the laboratories of the thousands of physicists who face them practically every day. And now, as if that were not enough, a team of researchers from Brown University, in Rhode Island, has just confirmed the existence of a new type of quantum particles, ‘fractional excitons’, whose unexpected behavior could significantly expand our understanding of the rules that govern the subatomic realm. “Our findings – says Jia Li, first author of a recent article published in ‘Nature’ – point towards a completely new class of quantum particles that have no overall charge but follow unique quantum statistics. The most exciting part is that this discovery unlocks a variety of new quantum phases of matter, presenting a new frontier for future research, deepening our understanding of fundamental physics, and even opening up new possibilities in quantum computing.” Neither bosons, nor fermions Together to his colleagues, Li’s discovery focuses on a well-known phenomenon, the ‘fractional quantum Hall effect’, which is based on the classical Hall effect, in which a magnetic field is applied to a material with an electric current to create a lateral voltage. The quantum Hall effect, which occurs at extremely low temperatures and in the presence of high magnetic fields, shows that this lateral stress increases in clear, well-defined steps. In the fractional quantum Hall effect, these steps become even more peculiar, increasing only by fractional amounts, carrying a fraction of the charge of an electron. For their experiments, the researchers built a structure with two thin layers of graphene, a nanomaterial two-dimensional, separated by an insulating hexagonal boron nitride crystal. This configuration allowed them to carefully control the movement of electrical charges, and also generate particles known as excitons, which are formed by combining an electron and the absence of another electron, known as a ‘hole’. They then exposed the system to extraordinarily strong magnetic fields, millions of times stronger than Earth’s. Which helped the team observe the new fractional excitons, which showed an unusual set of behaviors. Fundamental particles can be classified into two categories. On the one hand, bosons, which are the carriers of the forces of nature (photons, gluons, W and Z bosons, Higgs boson…) and which can share the same quantum state, that is, many of them can exist together without restrictions. And on the other hand, fermions, which are the constituents of matter and follow the so-called ‘Pauli exclusion principle’, according to which it is impossible for two fermions to occupy the same quantum state. But the fractional excitons discovered by Li and his team do not fit neatly into either category. In fact, and although they had the fractional charges expected in the experiment, their behavior showed tendencies of both bosons and fermions, acting almost like a hybrid of the two. That made them more similar to anyones, a type of ‘quasiparticle’ that is halfway between fermions and bosons; but with a series of unique properties that also differentiated them from anyones. A new class of particles “This unexpected behavior – explains Naiyuan Zhang, co-author of the research – suggests that fractional excitons could represent a completely new class of particles with quantum properties unique. We show that excitons can exist in the fractional quantum Hall regime and that some of these excitons arise from the pairing of fractionally charged particles, creating fractional excitons that do not behave like bosons.” According to the researchers, the existence of this new class of particles could one day help improve the way information is stored and manipulated at the quantum level, leading to faster and more reliable quantum computers. “Basically,” says Li, “we have unlocked a new dimension to explore and manipulate this phenomenon, and we are just beginning to scratch its surface. This is the first time that it has been experimentally demonstrated that this type of particles really exists, and now we are delving into what could arise from them. MORE INFORMATION news If They measure, for the first time, the ‘quantum geometry’ of electrons news No NASA lowers its ambition with the Mars sample return mission “It seems as if we have our finger right on the button of quantum mechanics,” says co-author Dima Feldman. “It is an aspect of quantum mechanics that we did not know or, at least, did not understand until now.”
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