Long-sought particles possibly glimpsed

Majorana fermions, which are their own antiparticle, could prove useful in quantum computing

The hunt for an elusive particle that does not have a distinct antiparticle twin might be over. Dutch physicists report making a new device that appears to create the mysterious entity, called the Majorana fermion.

“It is the fulfillment of a great intellectual challenge that has been with us since 1937,” says Marcel Franz, a physicist at the University of British Columbia in Vancouver. The work, led by Leo Kouwenhoven of the Delft University of Technology, appears online April 12 in Science.

Fundamental subatomic particles that make up matter, such as electrons, have antimatter companions. But Majorana fermions, first theorized over 70 years ago, are a class of particles that are their own antiparticle. They might have potential applications for storing data in future quantum computers.

Previously, scientists have published theoretical ideas or instructions on how to engineer the elusive Majorana fermions. Until now, no team has actually constructed such a device.

In the new work, Kouwenhoven’s team assembled a device using an indium antimonide nanowire about 100 nanometers across, about the size of an HIV particle. The scientists put a gold metal electrode at one end of the wire and a superconducting electrode near the other end, then applied a magnetic field.

Surprisingly, the scientists found that maximum electric charge moved from the gold electrode end through to the superconductor end at zero voltage. This pattern suggests that a pair of Majorana fermions formed at the opposing ends of the nanowire, Kouwenhoven says. Otherwise, scientists would not have expected to see electric charge being able to navigate the gap between the thin wire and the superconductor.

When the physicists adjusted the components of this recipe, by changing the direction of the magnetic field or removing the superconductor, the behavior disappeared. “We took out, one by one, these necessary ingredients,” Kouwenhoven says. “Every time we take out one of these special ingredients the Majorana disappeared.”

Though promising, this work is not definite evidence.

“I would not describe this as a discovery yet,” says Patrick Lee, a condensed matter physicist at MIT. Lee says the study’s conductance measurements need to be more precise to prove the existence of these particles. “There could be a Majorana hiding behind there,” he says. “It’s not an open and closed case.”

Others think these findings open up new possibilities for quantum computing, the idea of using quantum particles for storing data. Unlike typical quantum particles, whose information tends to be easily destroyed, Majorana fermions might make more durable storage units. Destroying Majorana fermions — and any data they could potentially store — also means coordinating an attack of its two separated ends at the exact same time. So data are less likely to be wiped out accidentally. 

“I’m not sure if this thing will ever be scaled up to a system that will be on your desktop,” says Taylor Hughes, a theoretical physicist at the University of Illinois at Urbana-Champaign. “But this is the first step in showing that type of architecture.”

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