Superconductor with unconventional interface could benefit quantum computing

A multi-institutional team of scientists in the United States, led by physicist Peng Wei of the University of California, Riverside, has developed a new superconducting material that could potentially be used in quantum computing and be a candidate “topological superconductor.”

Topology is the mathematics of shape. A topological superconductor uses a delocalized state of an electron or hole (a hole behaves like an electron with a positive charge) to carry quantum information and process data robustly.

The researchers report in Scientific progress that they combined trigonal tellurium with a surface-state superconductor generated on the surface of a thin gold film. The title of the paper is “Signatures of a spin-active interface and a locally enhanced Zeeman field in a chiral-superconducting material heterostructure.”

Trigonal tellurium is a chiral material, meaning it cannot be superimposed on its mirror image, like our left and right hands. Trigonal tellurium is also nonmagnetic. However, the researchers observed quantum states at the interface that harbor a well-defined spin polarization. The spin polarization allows the excitations to potentially be used to create a spin quantum bit, or qubit.

“By creating a very clean interface between the chiral material and gold, we developed a two-dimensional interface superconductor,” said Wei, associate professor of physics and astronomy.

“The interface superconductor is unique because it lives in an environment where the spin energy is six times higher than that of conventional superconductors.”

The researchers observed that the interface superconductor undergoes a transition under a magnetic field and becomes more robust at high field compared to low field, suggesting a transition to a “triplet superconductor,” which is more stable under a magnetic field.

Additionally, through a collaboration with scientists at the National Institute of Standards and Technology, the researchers showed that such a superconductor involving heterostructured gold and niobium thin films naturally suppresses sources of decoherence from material defects such as niobium oxides that are a common challenge for niobium superconductors.

They showed that the superconductor can be transformed into high-quality, low-loss microwave resonators with a quality factor of up to 1 million.

The new technology has applications in quantum computing, a field that leverages quantum mechanics to solve complex problems that classical computers or supercomputers can’t solve or can’t solve quickly enough, according to multinational technology company IBM.

“We achieved this result using materials that are an order of magnitude thinner than those typically used in quantum computing,” Wei said. “Low-loss microwave resonators are essential components of quantum computing and could lead to low-loss superconducting qubits. The biggest challenge in quantum computing is to reduce decoherence, or the loss of quantum information in a qubit system.”

Decoherence occurs when a quantum system interacts with its environment, leading to confusion of the system’s information with the environment. Decoherence poses a challenge for the realization of quantum computers.

Unlike previous methods that require magnetic materials, the researchers’ new approach uses non-magnetic materials for a cleaner interface.

“Our material could be a promising candidate for developing more scalable and reliable quantum computing components,” Wei said.

Wei was joined in his research by his UCR graduate students.

The technology was disclosed to UCR’s Office of Technology Partnerships and a provisional patent was filed.