Peculiar superconductor aids quest for quantum computing
Humanity has been on the trail of the elusive and mysterious Majorana fermion since it was first theorized in 1937. Now, researchers at Chalmers University of Technology think they have manufactured a topological superconductor capable of hosting the mysterious particle. If so, this could be an important step towards practical and robust quantum computers which don't lose data.
What are Majorana fermions?
Majorana fermions are among those tricky subatomic particles that don't seem to make a good deal of sense viewed through the lens of everyday experience. For example, what separates the Majorana particle from other fermions such as protons, electrons and quarks, is that it is its own antiparticle. As weird as that sounds, this made sense to Ettore Majorana in 1937, who first theorized that such a particle exists.
But they weren't detected until the last few years. So far, they've been observed as quasiparticles, which only exist under very specific sets of circumstances. You can find out more in our report from last July.
How do they help quantum computing?
It's their insensitivity to decoherence that the quantum computing world is so interested in. The power of a quantum computer derives from quantum phenomena including superposition of quantum bits: their ability to hold the value 0, 1, or, unlike a regular digital bit, both at the same time.
But these superpositions are prone to collapse, thereby losing information — a phenomenon known as quantum decoherence. It's thought that encoding a pair of Majorana fermions which are separated in a material will make them immune to this information loss.
So what's the catch?
The problem is that to achieve all this you need a topological superconductor – a superconductor which hosts Majorana fermions on its surface. And unfortunately topological superconductors don't grow on trees: attempts to create them are at the cutting edge of research in the field. Attempts to pin down Majorana particles and topological superconductors are inextricable.
But the Chalmers researches have managed?
"Our experimental results are consistent with topological superconductivity," says Profressor Floriana Lombardi. Yet Chalmers' press release sounds a note of caution. "After an intensive period of analyses the research team was able to establish that they had probably succeeded in creating a topological superconductor."
Probably is an interesting word, and we've asked the researchers what, if anything, is the cause of doubt.
But what did the researchers do, exactly?
The team applied a layer of aluminum superconductor onto a topological insulator of bismuth telluride (Be2Te3). "The superconducting pair of electrons then leak into the topological insulator which also becomes superconducting," says Associate Professor Thilo Bauch.
Though the first readings pointed to standard conductivity in the insulator, later readings, taken after another cooling of the component, differed. These showed change in the insulator's superconducting properties, with the pairs of electrons varying in different directions — results inconsistent with conventional superconductivity. After looking further into the results, the team concluded that they'd succeeded in making a topological conductor. Probably.
What happens next?
"For practical applications the material is mainly of interest to those attempting to build a topological quantum computer," Lombardi explains. "We ourselves want to explore the new physics that lies hidden in topological superconductors — this is a new chapter in physics."
The team's paper is published in the journal Nature Communications.
Update March 3: Floriana Lombardi and Thilo Bauch got back to us with answers to a few queries. On the significance of this research, they explain that before this work could be applied to quantum computer architecture, experiments to observe Majorana fermions are needed, which is indeed the next step.
On the question as to whether this was indeed a topological superconductor, the pair explain that there is no other explanation that would fit the full set of results seen. However, as there's no full theoretical model describing this complex device, a degree of healthy caution is appropriate. It's good to see that caution made it across to the press release.