Penn State researchers have developed an advanced topological superconductor that improves the stability of the quantum computer – a major limitation of the technology.
The team has innovated a new method for fusing two materials – a single-layer superconductor and a topological insulator – with particular electrical properties. The combination provides an optimal platform for studying an unusual type of superconductivity known as topological superconductivity, which could pave the way to topological quantum computers that are significantly more stable than conventional technology.
The team’s research, titled “Crossover from Ising- to Rashba-type superconductivity in epitaxial Bi2Se3/monolayer NbSe2 heterostructures’, is published in Natural materials.
Development of a topological superconductor
Superconductors are used in a variety of technologies, including powerful magnets, digital circuits, and imaging. They allow electric current to flow without resistance. In contrast, topological insulators are thin films only a few atoms thick that restrict the movement of electrons, resulting in unique properties. Penn State researchers have now developed a way to combine the two materials.
Cui-Zu Chang, associate professor of physics at Penn State and leader of the research team, commented: “The future of quantum computing depends on a type of material we call a topological superconductor, which can be formed by combining a topological insulator with a superconductor, but the actual process of combining these two materials is difficult.
“In this study, we used a technique called molecular beam epitaxy to synthesize both topological and superconducting insulating films and create a two-dimensional heterostructure that provides an excellent platform to explore the phenomenon of topological superconductivity.”
Previous attempts to fuse the two materials have yielded poor results, as superconductivity in thin films usually disappears after the topological insulator layer has grown. The experts were able to apply a topological insulating film to a three-dimensional “bulk” superconductor and retain the properties of both materials. However, applications of topological superconductors, such as low-power chips for smartphones and quantum computers, are expected to be two-dimensional.
Researchers overcame these problems to innovate a two-dimensional topological superconductor by stacking a topological insulating film made of bismuth selenide (Bi2Se3) with different thicknesses on a superconducting film made of monolayer niobium diselenide (NbSe2). The team succeeded in retaining the topological and superconducting properties by synthesizing the heterostructures at very low temperatures.
Hemian Yi, a postdoctoral researcher with the Chang Research Group at Penn State and first author of the paper, explained: “In superconductors, electrons form ‘Cooper pairs’ and can flow with zero resistance, but a strong magnetic field can break these pairs. .
“The single-layer superconducting film we used is known for its ‘Ising-type superconductivity’, which means that Cooper pairs are highly resistant to in-plane magnetic fields. We would also expect the topological superconducting phase formed in our heterostructures to be robust in this way.
Solve stability problems of quantum computers
The researchers found that by adjusting the thickness of the topological layer, the heterostructure changed from Ising-type superconductivity (where the electron spin is perpendicular to the film) to Rashba-type superconductivity (where the electron spin is parallel to the film). film). They also observe this phenomenon in their theoretical calculations and simulations.
This heterostructure could be an ideal platform for exploring Majorana fermions – an enigmatic particle that would help develop a topological quantum computer that is more stable than previous versions of the technology.
Change concluded, “This is an excellent platform for the exploration of topological superconductors, and we hope to find evidence for topological superconductivity in our continued work. Once we have strong evidence for topological superconductivity and demonstrate Majorana physics, this type of system could be suitable for quantum computing and other applications.
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