Majorana particle glimpsed in lab

Scientists think they may finally have seen evidence for a famously elusive quarry in particle physics.

The Majorana fermion was first predicted 75 years ago - a particle that could be its own anti-particle.

Now Dutch researchers, who have devised some exotic and minute circuitry to test for the Majorana's existence, believe their results show the fermion to be real.

The team has reported the details of its experiments in Science magazine.

"It opens up some very interesting ideas," said Leo Kouwenhoven from the Delft University of Technology.

Majoranas should behave quite differently from more familiar matter particles, such as electrons.

When these confront their opposites - positrons - they annihilate each other in a flash of gamma rays.

The idea that a particle existed that might be equal to its anti-particle was put forward by Italian Ettore Majorana, a brilliant theorist who mysteriously went missing after withdrawing all his money to go on a boat journey in 1938.

Many have tried to prove his fermion's existence, with a lot of the recent interest pursued not in giant accelerators, which have traditionally hunted new particles, but rather in incredibly small electronic devices where lengths are measured on the order of just billionths of a metre (nanometres).

Down to the wire
Prof Kouwenhoven's group fabricated just such a device with the help of colleagues from the Eindhoven University of Technology.

It comprised a phenomenally thin wire in contact with a semiconductor and a superconductor.

When a magnetic field was applied along the length of this "nanowire", electrons in it were restricted to a certain set of energies. But the set-up created a specific gap in energy in which electrons could gather together, acting in synchrony as a Majorana particle.


The nanowire created a place where the Majorana particles could be sequestered
The team applied a voltage to the wire, measuring the degree to which the wire conducted electricity at several points along its length.

The scientists say they saw two distinct dips in this conductance, one at either end of the wire. This is where they believe the Majorana particles were hiding.

"If you take a solid material and you make the right combinations, the natural particles living in these condensed matter structures, will also obey this defining property of Majorana fermions - that a particle is equal its anti-particle," Prof Kouwenhoven told BBC News.

"The system is still built out of atoms, with nuclei and electrons, but the electrons behave together in such a way that their collective state is a Majorana fermion."

Other groups working in this field of solid state physics are thought to be close to making similar announcements.

Probing the novel properties of Majorana particles could allow scientists to understand better the mysterious realm of quantum mechanics, which explains the behaviour of matter and its interactions with energy on the very smallest scales.

Those properties are also expected to make the fermions ideally suited to be the stable "bits" of information in the long-talked-about quantum computer, a theoretical device that would make use of quirky quantum effects to perform computation at incredible speeds.

And it has even been suggested that the "missing mass" in the Universe - the matter we cannot detect directly but which we know to exist because of its gravitational influence on everything we can see - is made up in some part by Majorana particles.