Peaceful matter-antimatter pairing looks more real

MATTER and antimatter have been caught coexisting ? again. A second attempt to detect long-sought Majorana fermions, particles that can act as their own antiparticle, has come up positive, suggesting the strange particles are real.

Fermions such as electrons and quarks, the particle building blocks of matter, have antiparticles that are identical except for their charge. When the two meet, they annihilate in a puff of energy. But in 1937, Italian physicist Ettore Majorana proposed a hypothetical particle that is its own antiparticle. Both would have zero charge and the two could coexist without annihilating.

The first signs of these Majorana fermions came last year in the form of a current that appeared at zero voltage in a nano-size wire. That should not happen ? normally, you need voltage to make electrons flow. But if two Majorana fermions were sitting at either end of the wire, each in the form of a hybrid between an electron and its positively charged partner, an electron-free "hole", then that could produce such a blip.

Now Dale Van Harlingen and colleagues at the University of Illinois at Urbana-Champaign have further evidence that this is the correct explanation. They created a similar set-up but this time ramped the voltage up and down and shortened the wire. The plan was to cause the quantum waves associated with each fermion to overlap and constructively interfere, creating two extra peaks in current. Sure enough, the team saw two more blips (Physical Review Letters, doi.org/kzj).

"This increases our faith that this is indeed the physics of Majorana," says Sankar Das Sarma of the University of Maryland in College Park, who predicted the double signal in December. But he is still cautious: "I would still not say that I would bet my whole salary on this, but I'm getting there."

This article appeared in print under the headline "Peaceful matter-antimatter pairs are the real deal"

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