Found: Traces of Exotic Particle That Eluded Physicists for 80 Years
Physicists used a scanning tunneling microscope to capture an image of the neutral charge signature of the Majorana fermion at the end of the wire.
Credit: Yazdani Lab/Princeton University

A mysterious particle made of both matter and antimatter has eluded physicists for 80 years, but now, researchers have spotted traces of it.

Physicists think each particle has its own antiparticle with the same mass but an opposite charge. But the new particle, called a Majorana (pronounced mai-yor-ah-na) fermion, acts as its own antimatter partner and has a neutral charge. The particle is puzzling, because physicists know that when matter and antimatter collide, they annihilate each other. In the 1930s, physicist Ettore Majorana proposed that a particle existed that was made of both matter and antimatter; even so, physicists could not find any trace of the particle — until now.

Tricky experiment

Catching a glimpse of this sneaky particle was not easy. Ali Yazdani, a professor of physics at Princeton University, and colleagues used a giant, two-story microscope to zero in on a tiny iron wire only a few atoms long. They placed the wire on top of a chunk of lead and cooled it to minus 458 degrees Fahrenheit (minus 272 degrees Celsius), or near absolute zero. [The 9 Biggest Unsolved Mysteries in Physics]

The extreme cold created a superconductive state in the lead. (A superconductor can channel electricity with zero resistance.) The balance between the magnetic field from the iron wire and the superconductivity from the lead produced the Majorana fermions that hovered at the ends of the wire.

Since the wire was long enough, the matter and antimatter could hang out on opposite ends and not annihilate each other, Yazdani said.

"Matter and antimatter can exist in isolation when they're not talking to each other," Yazdani told Live Science.

Using the huge microscope, the researchers detected neutral signals coming from the ends of the wire — the key signature of Majorana fermions that decades of research and calculations have predicted. This detection method is different from that used to elucidate other exotic particles, like the Higgs boson, which was detected inside the Large Hadron Collider (LHC), the world's largest atom smasher. The LHC smashes atoms together at near light speed and creates particles in a vacuum.

Yazdani and the team designed their experiment based on a theory developed by Alexei Kitaev, a professor of physics at the University of California, Santa Barbara. In 2001, Kitaev predicted that a certain type of superconductive state would produce the Majorana fermions and that the particles would show up on the ends of a wire.

It took Yazdani and the team two years to get the balance between the magnetic field and the superconductive state just right, but the Majorana fermions finally emerged at the ends of the wire. The researchers could pinpoint the Majorana particles because their matter and antimatter components make them electrically neutral. The giant scanning tunneling microscope, which can image surfaces at the atomic level, captured images of the neutral electric signals.

Holy Grail of quantum computing?

Majorona fermions could be perfect for creating quantum computers. In regular computers, information is stored in "bits," each of which is coded as either a 0 or a 1. In a quantum computer, those bits of information would exist simultaneously as both a 0 and a 1. But this strange "superposition" state is very fragile.

"To get these states, you have to turn off interaction with the environment, because any interference can collapse the system," Yazdani said.

So physicists have been on the lookout for a way to make quantum bits more stable. Majorana fermions are surprisingly stable for being made of two elements that are supposed to annihilate each other. The matter and antimatter in a Majorana fermion also gives it a neutral charge so it barely interacts with its environment. These properties could make the Majorana fermion a much more stable way to encode quantum information, since their superposition state would be more resistant to collapse, physicists say.

Majorana fermions are also candidate particles for mysterious dark matter. Dark matter makes up almost 27 percent of the universe, but physicists still haven't directly detected it. Many scientists think the particles that make up dark matter must be difficult to detect and probably don't interact much with their environment — exactly like Majorana fermions

Yazdani said the next step is to see if the team can manipulate the Majorana fermions. Results of the experiment were published Oct. 2 in the journal Science.

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