Upgrade your PC to Quantum

Image: Researchers at the University of Tokyo grow a nanolayer of a superconducting material on top of a nitride-semiconductor substrate, which may help facilitate the integration of quantum qubits with existing microelectronics.
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Credit: Institute of Industrial Sciences, University of Tokyo

TOKYO, Japan – Computers that can take advantage of the “scary” properties of quantum mechanics to solve problems faster than current technology may seem tempting, but first a huge flaw must be overcome. Scientists from Japan may have found the answer by demonstrating how a superconducting material, niobium nitride, was added to a semiconducting nitride substrate as a flat crystal layer. This process could lead to the easy fabrication of quantum qubits connected to classical computers.

The processes used to manufacture traditional silicon microprocessors have matured over decades and are constantly being refined and improved. In contrast, most quantum computing architectures have to be designed mostly from scratch. However, finding a way to add quantum capabilities to existing manufacturing lines, or even integrate quantum and classical logic units into a single chip, may be able to significantly accelerate the adoption of these new systems.

Now, a team of researchers at the University of Tokyo’s Institute of Industrial Sciences has shown how thin films of niobium nitride (NbN)x) directly on top of the aluminum nitride (AlN) layer. Niobium nitride can become superconducting at temperatures below about 16 degrees above absolute zero. As a result, it can be used to create a superconducting qubit when arranged in a structure called a Josephson junction. Scientists investigated the effect of temperature on the crystal structures and electrical properties of NbNx Thin films grown on AlN template substrates. They showed that the spacing of atoms in the two materials was compatible enough to produce flat layers. “We found that due to the small lattice mismatch between aluminum nitride and niobium nitride, a highly crystalline layer could grow at the interface,” says first author and concurrence of Atsushi Kobayashi.

Crystallization of NbNx It was characterized by X-ray diffraction, and the surface topology was captured using atomic force microscopy. In addition, the chemical composition was examined using X-ray spectroscopy. The team showed how the arrangement of atoms, nitrogen content and electrical conductivity all depend on growing conditions, particularly temperature. “The structural similarity between the two materials facilitates the integration of superconductors in semiconductor photovoltaic devices,” says Atsushi Kobayashi.

Moreover, the sharply defined interface between the AlN substrate, which has a wide band gap, and NbNx, a superconductor, essential for future quantum devices, such as Josephson junctions. Superconducting layers only a few nanometers thick and with a high crystallinity can be used as single photon or electron detectors.

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The work was published in Advanced Material Interfaces as “a supra-axial growth governed by the crystal phase of NbNx Superconductors in a wide bandgap AlN semiconductor” (DOI: 10.1002 / admi.202201244).

About the Institute of Industrial Sciences, University of Tokyo

The University of Tokyo Institute of Industrial Sciences (UTokyo-IIS) is one of the largest university-related research institutes in Japan. UTokyo-IIS consists of more than 120 research laboratories – each headed by a faculty member – and has more than 1,200 members (about 400 staff and 800 students) who are actively involved in education and research. Its activities cover almost all fields of engineering. Since its founding in 1949, UTokyo-IIS has worked to bridge the huge gaps that exist between academic disciplines and real-world applications.


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