Unconventional superconductor may be used to create quantum computers of the future

February 19, 2018, Chalmers University of Technology
After an intensive period of analyses the research team led by Professor Floriana Lombardi, Chalmers University of Technology, was able to establish that they had probably succeeded in creating a topological superconductor. Credit: Johan Bodell/Chalmers University of Technology

With their insensitivity to decoherence, Majorana particles could become stable building blocks of quantum computers. The problem is that they only occur under very special circumstances. Now, researchers at Chalmers University of Technology have succeeded in manufacturing a component that is able to host the sought-after particles.

Researchers throughout the world are struggling to build quantum computers. One of the great challenges is to overcome the sensitivity of quantum systems to decoherence, the collapse of superpositions. One track within quantum computer research is therefore to make use of Majorana particles, which are also called Majorana fermions. Microsoft, among other organizations, is exploring this type of quantum computer.

Majorana fermions are highly original particles, quite unlike those that make up the materials around us. In highly simplified terms, they can be seen as half-electron. In a quantum computer, the idea is to encode information in a pair of Majorana fermions separated in the material, which should, in principle, make the calculations immune to decoherence.

So where do you find Majorana fermions? In solid state materials, they only appear to occur in what are known as topological . But a research team at Chalmers University of Technology is now among the first in the world to report that they have actually manufactured a topological superconductor.

"Our experimental results are consistent with ," says Floriana Lombardi, professor at the Quantum Device Physics Laboratory at Chalmers.

To create their unconventional superconductor, they started with what is called a made of bismuth telluride, Bi2Te3. A topological conducts current in a very special way on the surface. The researchers placed a layer of aluminum, a conventional superconductor, on top, which conducts current entirely without resistance at low temperatures.

"The superconducting pair of electrons then leak into the topological insulator, which also becomes superconducting," explains Thilo Bauch, associate professor in quantum device physics.

However, the initial measurements all indicated that they only had standard superconductivity induced in the Bi2Te3 topological insulator. But when they cooled the component down again later, to routinely repeat some measurements, the situation suddenly changed—the characteristics of the superconducting pairs of electrons varied in different directions.

"And that isn't compatible at all with conventional superconductivity. Unexpected and exciting things occurred," says Lombardi.

Unlike other research teams, Lombardi's team used platinum to assemble the topological insulator with the aluminum. Repeated cooling cycles gave rise to stresses in the material, which caused the superconductivity to change its properties. After an intensive period of analyses, the researchers established that they had probably succeeded in creating a topological superconductor.

"For practical applications, the material is mainly of interest to those attempting to build a topological computer. We want to explore the new physics hidden in —this is a new chapter in physics," Lombardi says.

The results were recently published in Nature Communications in a study titled "Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator."

Explore further: Spin-polarized surface states in superconductors

More information: Sophie Charpentier et al, Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator, Nature Communications (2017). DOI: 10.1038/s41467-017-02069-z

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5 / 5 (1) Feb 19, 2018
But there aren't quantum computers of the present yet...
1 / 5 (1) Feb 19, 2018
Repeated cooling cycles gave rise to stresses in the material (see image below), which caused the superconductivity to change its properties
This picture is probably this one - most online media which reposted this story didn't bother to attach it...

But there aren't quantum computers of the present yet..
A large Quantum computer project in the Wallenberg Quantum Technology Centre is underway at Chalmers University of Technology. It is, however, based on technology other than topological superconductors.
1 / 5 (1) Feb 19, 2018
The topological insulation is mostly relativistic effects. Inside heavy elements like bismuth or tellurium the outer electrons are propagating in so high speed, their orbits are subject of relativist contraction and these electrons get expelled from atoms to their surface and squeezed there. The similar effect applies to high temperature ("inconventional") superconductors, where the electrons get squeezed around hole stripes. But because electrons can still move freely at the surface, this effect is weaker for topological insulators and their electrons are only "highly conductive". The above study did show, though, that repeated cycles of cooling and heating induced a thermal stress inside the surface layer in such a way, the motion of electrons got constrained even more up to level, that superconductive stripes were still formed there. This observations therefore points to close similarity of (free electron states within) topological insulators and high-temperature superconductors.
1 / 5 (1) Feb 19, 2018
I perceive a bit surprising, that mainstream scientists still didn't bother to replicate the famous J.F.Prins observation with surface electrons at the diamond surface. Instead of vague thermal stress J.F.Prins attached the electrons to a surface by implantation of positively charged oxygen holes beneath the surface of diamond and what he got was robust superconductivity at room temperature.

The above study is already quite close conceptually to Prins experiments - yet the scientists continue in their dumb way of research, as if nothing would be ever published. A similar attitude can be observed in virtually all branches of physics, once it faced some unconventional finding, which could significantly streamline the existing research and to steal researchers for their safe perspective of jobs and grants. It points to the way, in which the mainstream research remains driven by occupational principle heavily.
5 / 5 (1) Feb 19, 2018
Do woo masters like mackita know how many people have them on their ignore lists or are they as ignorant of the fact that they are shouting into a vacuum as they are about everything else?
not rated yet Feb 20, 2018
Upton Sinclair — 'It is difficult to get a man to understand something, when his salary depends on his not understanding it.'
not rated yet Feb 20, 2018
Cryptography that is complicated never works, since its too hard for users/clients/businesses to understand without a phd in physics inorder to read about it. Making crypto easy is a facet of every resaercher, its not about confusion with needless terms.

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