A joint team of scientists at the University of California at Riverside and the Massachusetts Institute of Technology is coming closer to confirming an exotic quantum particle called Majorana-Fermion, which is crucial for fault-tolerant quantum computing ̵
Quantum computing uses quantum phenomena to perform calculations. Majorana fermions exist at the boundary of special superconductors, called topological superconductors, which have a superconducting gap in their interior and harbor majorana fermions outside their boundaries. Majorana fermions are one of the most sought objects in quantum physics because they are their own antiparticles, can divide the quantum state of an electron in half, and follow different statistics compared to electrons. Although many claimed to have identified them, scientists still can not confirm their exotic quantum nature.
The UCR-MIT team has mastered the challenge by developing a new gold-based heterostructure material system that could potentially be used to prove existence and quantum nature of Majorana fermions. Heterostructure materials consist of layers of drastically different materials, which together have completely different functionalities compared to their individual layers.
"It is most unimportant to find a material system that is inherently a topological superconductor," said Peng Wei, an assistant professor of physics and astronomy and a condensed matter experimenter, who co-authored the study with Jagadeesh Moodera and Patrick Lee of MIT in Physical Review Letters . "A material must meet several stringent conditions to become a topological superconductor."
It is predicted that the majorana fermion, which is considered to be half of an electron, is located at the ends of a topological superconductor nanowire. Interestingly, two majorana fermions can combine to form an electron, allowing the quantum states of the electron to be stored nonlocally, an advantage for fault-tolerant quantum computing.
In 2012, MIT theorists, led by Lee, predicted that gold heterostructures could become a topological superconductor under severe conditions. Experiments by the UCR-MIT team have met all the necessary conditions for heterostructures of gold.
"Achieving such a heterostructure is extremely challenging, as we first had to address some material physics challenges," said Wei, a UCR alum to whom he returned to campus in 2016 from MIT.
Wei explained that research shows that superconductivity, magnetism and the spin-orbit coupling of electrons in gold can co-exist – a difficult challenge – and can be mixed manually with other materials through heterostructures.
"Superconductivity and magnetism do not usually co-exist in the same material," he added.
Gold is not a superconductor, nor are the electronic states on its surface.
"Our article shows that this is the first time that superconductivity can be brought into the surface state of gold, which requires new physics," he said. "We show that it is possible to make the surface state of gold a superconductor that has never been shown before."
The work also shows that the electron density of superconductivity can be tuned in the surface states of gold.  "This is important for the future manipulation of Majorana fermions required for better quantum computing," said Wei. "In addition, the surface state of gold is a two-dimensional system that is naturally scalable, allowing the construction of majorana fermion circuits."
The research team includes Wei, Moodera and Lee as well as Sujit Manna and Marius Eich from MIT.
Expect faster with quasi-particles
Peng Wei et al. Surface superconductivity of precious metal gold and Fermi-level tuning by EuS Dielectric, Physical Review Letters (2019). DOI: 10.1103 / PhysRevLett.122.247002
New material shows high potential for quantum computers (2019, 28th June)
retrieved on June 28, 2019
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