Professor Zhang Shouqi from Stanford University and his team recently announced a groundbreaking discovery in the journal *Science*: after 80 years of relentless pursuit, they have finally confirmed the existence of "Majorana Fermions." This discovery holds the potential to reshape our understanding of fundamental physics.
In 1928, the renowned British theoretical physicist Paul Dirac predicted that every elementary particle in the universe would have an antiparticle counterpart. When particles meet their antiparticles, they annihilate, releasing energy. Just a few years later, scientists discovered the first antiparticle—the positron, or electron's antiparticle—and antimatter quickly became a central topic in both science and popular culture.
However, in 1937, the Italian physicist Ettore Majorana proposed a revolutionary theory: he suggested that within the category of fermions—such as protons, neutrons, electrons, neutrinos, and quarks—there could exist a group of particles without antiparticles of their own.
Now, a team of scientists, including researchers from Stanford University, claims to have found definitive proof of Majorana fermions' existence. Collaborating with the University of California, they conducted a series of experiments on exotic materials in the lab and ultimately achieved this breakthrough.
Led by Jing Xi, an associate professor at the University of California, Irvine, and Kanglong Wang, a professor at the University of California, Los Angeles, the team followed a plan proposed by Zhang Shouqi and his Stanford colleagues. Their findings were published in the July 20 issue of *Science*.
As a prominent theoretical physicist and senior author of this research paper, Zhang Shouqi remarked: “Our team accurately predicted where to find Majorana fermions and what to look for as conclusive evidence of such particles. This discovery marks the end of one of the most extensive scientific quests in the realm of fundamental physics, spanning eight decades.â€
Zhang Shouqi also noted that the search for Majorana fermions was driven more by intellectual curiosity than immediate practical application. However, this exploration holds significant implications for the development of reliable quantum computers, even though this future remains distant.
Zhang Shouqi’s team observed a unique type of Majorana fermion known as the “chiral†fermion, which moves only in one direction along one-dimensional paths. The researchers emphasized that while designing and implementing experiments to produce these “chiral†Majorana fermions was highly challenging, the signals they detected were precise.
Tom Devereaux, Director of the Materials and Energy Research Division at the Stanford Linear Accelerator Center, commented: “This study represents the culmination of years of exploration into rival Majorana fermions.â€
Frank Wilczek, a Nobel laureate and theoretical physicist at MIT, said: “This appears to be a clear observation of something new.†Though not involved in the study, he added: “It’s not surprising, as physicists have long suspected that Majorana fermions might exist in the materials used in this experiment. However, combining several elements to clearly and reliably observe this new quantum particle is truly a landmark achievement.â€
Finding ‘Quasi-Particles’
Majorana’s predictions apply only to chargeless fermions, such as neutrons and neutrinos. Scientists have found antiparticles for neutrons, but they strongly suspect that neutrinos might be their own antiparticles. Currently, four experiments are underway, including the EXO-200 project at the Enriched Xenon Observatory in New Mexico. However, these experiments are extremely challenging, and answers are not expected for at least another decade.
About a decade ago, scientists realized that Majorana fermions could also emerge in certain material physics experiments, sparking a race to find them. What they’ve been searching for is “quasi-particlesâ€â€”particle-like excitations created by the collective behavior of electrons in superconducting materials, which conduct electricity with 100% efficiency.
According to Einstein’s famous equation E=mc², the process of generating these quasi-particles resembles how energy transforms into short-lived “virtual†particles in a vacuum and then reverts back to energy. Although quasi-particles aren’t naturally occurring particles, they are still considered genuine Majorana fermions.
Over the past five years, scientists have made some progress using this method, reporting sightings of Majorana fermion signatures in experiments involving superconducting nanowires. Yet Zhang Shouqi pointed out that in these cases, quasi-particles are “bound†to a specific location, making it difficult to conclusively rule out Other effects as the source of any observed signals.
Finding Hard Evidence
In a recent experiment at UCLA and UC Irvine, the team stacked two thin films of quantum materials—a superconductor and a magnetic topological insulator—and passed a current through them into a refrigerated vacuum chamber.
The top layer was a superconductor, while the bottom was a topological insulator that conducts current only along its surface or edge, not through its bulk. Combining them created a superconducting topological insulator where electrons moved along the two edges of the material’s surface without resistance, akin to cars on a highway.
Zhang Shouqi’s idea was to modify the topological insulator by adding a small amount of magnetic material. This caused electrons to flow unidirectionally along one edge of the surface, then reverse direction along the opposite edge. The researchers then swept a magnet over the stacked films, slowing the electron flow, halting it, and reversing it. These changes occurred in sharp steps, resembling the progression of a staircase.
At certain stages of this cycle, Majorana quasi-particles emerged—pairs appeared outside the superconducting layer and propagated like electrons along the edges of the topological insulator. Each particle in the aligned pair moved independently, enabling researchers to easily measure the flow of individual quasi-particles. Like electrons, their movement slowed, stopped, and reversed direction. These were precisely the signals the researchers had been seeking.
Gilorgio Gratta, who played a key role in the design and planning of the EXO-200, stated that these experimental results are unlikely to impact efforts to determine whether neutrinos are their own antiparticles.
Gratta said: “The quasi-particles they observed were essentially excitations in a material representing Majorana particles. But they are not elementary particles; they’re manufactured artificially in a specially prepared material. This cannot happen in the universe. On the other hand, neutrinos are ubiquitous, and if they are found to be Majorana particles, we will prove that nature not only makes such particles but uses them to fill the universe.â€
He added: “Interestingly, the analogy in physics has proven to be strong evidence, even if they are very different things and processes. Perhaps we can use one to understand the other and uncover something intriguing.â€
“Angel Particlesâ€
Zhang Shouqi envisions that Majorana fermions could one day be used to build robust quantum computers resistant to environmental noise. Since each Majorana fermion is effectively equivalent to only half of a subatomic particle, the information content of one qubit could be stored in two separate Majorana fermions, reducing some disturbances and preventing the loss of carried information.
Zhang Shouqi temporarily drew inspiration from Dan Brown’s 2000 bestseller *Angels and Demons*, naming the chiral Majorana fermion discovered by his team the “Angel Particle.†In the novel, a secret organization plans to destroy the Vatican with a time bomb powered by matter-antimatter reactions. Zhang Shouqi pointed out that, unlike the fictional scenario, in the “quantum world†of Majorana fermions, there are only angels and no devils.
[Images omitted for text-only format.]
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