Scientists have found the first firm evidence for the Majorana fermion, a particle that is its own particle. In the long term, this may have real-life implications for building robust quantum computers.
In 1928, a physicist called Paul Dirac hypothesised that every fundamental particle in the universe has an antiparticle - its identical twin but with opposite charge. This was confirmed a few years later when the first antimatter particle - the electron's opposite, the positron - was discovered.
About a decade later another physicist, called Ettore Majorana, predicted that some particles were also their own antiparticles.
Until now, they had not been observed experimentally by scientists. But in a study now published in the journal Science, researchers from the University of California in collaboration with Stanford University showed that it was possible to observe Majorana fermions.
"Our team predicted exactly where to find the Majorana fermion and what to look for as its 'smoking gun' experimental signature," said Shoucheng Zhang, a theoretical physicist and one of the senior authors of the research paper. "This discovery concludes one of the most intensive searches in fundamental physics, which spanned exactly 80 years."
The scientists stacked thin films of two quantum materials - a superconductor and a magnetic topological insulator - and sent an electrical current through them, all inside a chilled vacuum chamber.
Combining the two types of quantum material together, they created a superconducting topological insulator, where electrons zip along two edges of the material's surface without resistance. Then, adding a small amount of magnetic material to the system made the electrons flow one way along one edge of the surface and the opposite way along the opposite edge.
The next step was to sweep a magnet over the system, which made the flow of electrons slow, stop and switch direction.
During this cycle, the scientists observed Majorana quasiparticles emerging and following the same path as the electrons along the edges of the topological insulator. Like the electrons, they slowed, stopped and changed direction - but in steps exactly half as high as the ones the electrons took. This behaviour is characteristic of Majorana fermions, and as such, the scientists say this is the first robust evidence of the existence Majorana fermions.
The researchers also think that this discovery could in the future aid the construction of robust quantum computers that aren't thrown off by environmental noise. Up to now, this has made their development more challenging.
"Since each Majorana is essentially half a subatomic particle, a single qubit of information could be stored in two widely separated Majorana fermions, decreasing the chance that something could perturb them both at once and make them lose the information they carry," Zhang explained.