Every fundamental particle in the universe has an antiparticle, which has the same mass but the opposite charge. If a particle meets its antiparticle, the two would annihilate in a flash of energy. But it has long been theorized that there is an exception to the rule, with certain particles that are actually their own antiparticles.

Now, scientists at Stanford University and the University of California (UC) have found the first strong evidence for this type of particle, which they have dubbed " angel particle" A team of scientists from Stanford and UC says it has found the first firm evidence of such a Majorana fermion. It was discovered in a series of laboratory experiments on exotic materials at the University of California (UC), in collaboration with Stanford University. The team was led by UC-Irvaine Associate Professor Jing Xia and Professor Kang Wang of the University ofCalifornia at Los Angeles (UCLA), and followed a plan proposed by Shoucheng Zhang, a physics professor at Stanford, and colleagues. The team reported the results in a paper published in the Science .

The theory dates back to 1937, when Italian physicist Ettore Majorana highlighted a gap in the fermion family of particles. Protons, electrons, neutrons, neutrinos, and quarks are all fermions, and all have corresponding antiparticles, but according to Majorana's calculations, there must be particles that are their own antiparticles, which became known as Majorana Fermions .

Because they have no charge, neutrons and neutrinos were the best candidates to be these Majorana fermions, but antinutrons have been discovered. There is still a big question mark over neutrinos, and experiments are currently underway to determine whether they are actually their own antiparticle. However, the difficulty of the experiments implies that an answer is stillhas been more than a decade away from us.

Meanwhile, the most likely way to find Majorana fermions is to look for "quasi-particles." As the name suggests, these are not very natural particles, but arise from the collective behavior of electrons and possess certain properties of particles. If this is difficult to visualize, the Encyclopaedia Britannica explains the concept as bubbles in a drink: bubbles also arise from the "collective behavior" of chemicals in the drink, and while they are not truly independent objects, bubbles have measurable properties like real objects, including size, shape, etc.

Similarly, quasi-particles may not occur outside of very specific conditions, but can be considered Majorana fermions if they exhibit all the right properties. Now, researchers from Stanford and the Uinversity of California said they have found a " undeniable signature" (or "incontestable proof" or " smoking gun." the phrase that has often appeared in the media about the discovery) that points to the presence of these hypothetical fermions.

"Our team predicted exactly where to find the Majorana fermion and what to look for as its experimental signature of ' indisputable proof'" "This discovery concludes one of the most intensive researches in fundamental physics, which lasted exactly 80 years," says Shoucheng Zhang, one of the lead authors of the research paper.

To make these peculiar quasiparticles show, the team carefully constructed their very specific "drink" (as in the liquid conditions that produce the bubbles), composed of thin films of two quantum materials stacked on each other. The end result is a superconducting topological insulator, which allows electrons to move rapidly along the edges of the surface of theBy adding a pinch of magnetic material to the mixture, electrons flow in one direction along one edge, and in the opposite direction along the other.

The researchers then distributed a magnet over the material, which caused all the electrons to slow down, stop and alternate direction. The reversal happened in a jerky, staggered motion that the team compares to the steps on a staircase. The quasiparticles began to emerge from the material in pairs, traveling the same path as the electrons, but there was a fundamental difference:When they stopped and reversed the motion, they did so in "steps" on exactly half of the electrons. This is because each one is essentially only half a particle, since one of each pair of quasi-particles is lost along the way. And this phenomenon was exactly the evidence the researchers were looking for.

Zhang suggested that the team's discovery be called the "angel particle" in reference to Dan Brown's novel Angels and Demons, which features a bomb powered by the meeting of matter and antimatter. In the long run, Majoranas' fermions could find a practical application in making quantum computers safer.

The research

In 1928, physicist Paul Dirac made the stunning prediction that every fundamental particle in the universe has an antiparticle - that is, an identical twin particle but with opposite charge (the electric charges of particles and antiparticles and their angular moments have the same absolute values as their symmetric counterparts, yet the electromagnetic fields are of signscontrary).

When the particle and antiparticle meet, they are annihilated, releasing an amount of energy. A few years later, the first antimatter particle - the opposite of the electron, the positron - was discovered, and antimatter quickly became part of popular culture.

Matter + Antimatter = Energy. When a particle of matter collides with its antimatter both are transformed into pure energy, proportional to the mass consumed, generating energy according to E=mc².

But in 1937, the brilliant physicist, Ettore Majorana, introduced a twist: he predicted that in the class of particles known as fermions, which includes the proton, neutron, electron, neutrino and quark, there should be particles that are their own antiparticles.

"Our team predicted exactly where to find the Majorana fermion and what to look for as its experimental "undesirable signature," said Zhang, a theoretical physicist and one of the lead authors of the research paper. "This discovery concludes one of the most intensive researches in fundamental physics, which lasted exactly 80 years."

Although the search for the famous fermion appears to be more intellectual than practical, he added, it could have real-life implications in building robust quantum computers, although this is admittedly very much in the future.

The particular type of Majorana fermion, the research team noted, is known as a "chiral" fermion because it moves along a one-dimensional path in only one direction. Even though the experiments that produced it were extremely difficult to design, set up and carry out, the evidence they produced was clear and unambiguous, the researchers said.

"This research culminates a many-year pursuit to find chiral Majorana fermions. It will be a milestone in this area," said Tom Devereaux, director of the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC National Accelerator Laboratory, where Zhang is principal investigator.

"It really seems like a clear observation of something new," said Frank Wilczek, a theoretical physicist and Nobel laureate at the Massachusetts Institute of Technology (MIT), who was not involved in the study. "It's not fundamentally surprising, because physicists have long thought that Majorana fermions could arise from the kinds of materials used in this experiment. "But they put together severalelements that have never been put together before and also the engineering behind it, is a real milestone that have allowed then this new type of quantum particle to be observed clearly and robustly."

Searching for "quasiparticles"

Majorana's prediction applied only to fermions that had no charge, such as the neutron and neutrino. Scientists have already found an antiparticle for the neutron, but they have good reason to believe that the neutrino may be its own antiparticle, and there are four experiments underway to find out - involving the EXO-200, the latest generation of the Enriched Xenon Observatory (EXO), an Enriched Xenon Observatory But these experiments are extraordinarily difficult and are not expected to produce an answer for less than about a decade.

About ten years ago, scientists realized that Majorana fermions can also be created in experiments that explore materials physics - and the race was on to make it happen.

What they sought are "quasiparticles" - particle-like excitants that arise from the collective behavior of electrons in superconducting materials, which conduct electricity with 100 percent efficiency ( read the Ciência Hoje article on quasiparticles here The process that gives rise to these quasi-particles is similar to the way energy is transformed in the vacuum of space into short-lived "virtual" particles and back into energy again, according to Einstein's famous equation E = mc². Although quasi-particles are not like particles found in nature, they could nevertheless be considered real Majorana fermions.

Over the past five years, scientists have had some success with this approach, reporting that they had seen promising signatures of the Majorana fermion in experiments involving superconducting nanowires.

But in those cases, the quasi-particles were "confined" - stuck in a particular place, rather than propagating through space and time - and it was hard to tell if other effects were contributing to the signals the researchers saw, according to Zhang.

Smoking gun - the hot proof

In the latest experiments at UCLA and UC-Irvine, following the plan proposed by Stanford University researchers, the team stacked thin films of two quantum materials - a superconductor and a magnetic topological insulator - and ran an electric current through them, all inside an icy vacuum chamber.

The top film was the superconductor. The bottom was the topological insulator, which acts only along its surface or edges, but not through the medium. By putting them together, a superconducting topological insulator was created, where electrons slide along two edges of the material's surface without resistance, like cars on a superhighway.

It was Zhang's idea to tweak the topological insulator by adding a small amount of magnetic material to it. This caused electrons to flow one way along one edge of the surface and in the opposite direction along the other edge.

Then the researchers passed a magnet over the battery. This caused the flow of electrons to slow down, stop, and change direction. These changes were not smooth, but occurred in abrupt steps, like "identical steps on a ladder.

At certain points in this cycle, Majorana quasiparticles emerged, emerging in pairs from the superconducting layer and traveling along the edges of the topological insulator just as the electrons did. One member of each pair was deflected from the path, allowing the researchers to easily measure the flux of the individual quasiparticles that continued their journey. Like the electrons, theydecreased, stopped, and changed direction - but in "steps" of exactly half the height of the "steps" that the electrons presented.

These "half steps" were the hot evidence (or "undisputed proof" or " smoking gun" ) that the researchers were looking for.

The results of this research are unlikely to have any effect on efforts to determine whether the neutrino is its own antiparticle, said Stanford University physics professor Giorgio Gratta, who played a major role in the design and planning of the EXO-200 observatory.

"The quasiparticles they observed are essentially excitations in a material that behaves like Majorana particles," Gratta said. "But they are not elementary particles and are made very artificially in a specially prepared material.They are very unlikely to occur in the universe, although who are we to say? "On the other hand, neutrinos are everywhereplaces, and if they are Majorana particles, we would show that nature not only made these kinds of particles possible, but in fact literally filled the universe with them."

He added: "Where it gets most interesting is that analogies in physics have proven to be very powerful. And even though they're very different beasts, different processes, maybe we can use one to understand the other. Maybe we can figure out something that's interesting to us as well."

Angel particle

In the future, Zhang said, Majorana fermions could be used to build robust quantum computers that are not disrupted by environmental "noise" (environmental interference), which has been a major obstacle to the development of such equipment. Since each Majorana is essentially half of a subatomic particle, a single qubit of information could be stored in two completely separate Majorana fermions, decreasing the chance that something could disturb them at once and cause them to lose the information they carry.

For now, he suggests a name for the chiral Majorana fermion that his team discovered: the "angel particle," in reference to the best-selling suspense novel of the 2000s: Dan Brown's "Angels and Demons. In the novel, a secret fraternity plans to blow up the Vatican with a time bomb, whose explosive power comes from the annihilation of matter and antimatter. Unlike the book, henoted, in the quantum world of the Majorana fermion there are only angels - no demons.Sources ;

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O'CALLAGHAN, Jonthan. "Researchers Discover "Angel Particle" Which Is Both Matter And Antimatter At The Same Time" Accessed 27/0/2017.