Computers that can utilize the “spooky” properties of quantum mechanics to solve problems faster than current technology may sound enticing, but they must first overcome a significant disadvantage. Japanese scientists may have found the answer by demonstrating how a superconducting material, niobium nitride, can be added as a flat, crystalline layer to a nitride-semiconductor substrate. This procedure may facilitate the production of quantum qubits connected to conventional computer hardware.
The processes used to manufacture conventional silicon microprocessors have been refined and improved over decades. In contrast, the vast majority of quantum computing architectures must be created from scratch. But finding a way to add quantum capabilities to existing fabrication lines or putting both quantum and traditional logic units on a single chip could greatly speed up the spread of these new systems.
Now, a team of researchers from the University of Tokyo‘s Institute of Industrial Science has demonstrated how thin films of niobium nitride (NbNx) can be grown directly on top of an aluminum nitride (AlN) layer. Niobium nitride is superconducting at temperatures below 16 degrees above absolute zero. Consequently, it can be used to create a superconducting qubit when arranged in a Josephson junction. The researchers examined the influence of temperature on the crystal structures and electrical properties of NbNx thin films grown on AlN template substrates. They demonstrated that the atomic spacing of the two materials was compatible enough for the formation of flat layers. Due to the small lattice mismatch between aluminum nitride and niobium nitride, we discovered that a highly crystalline layer could grow at the interface, explains lead author and corresponding author Atsushi Kobayashi.
X-ray diffraction was used to determine the crystallinity of NbNx, while atomic force microscopy was used to capture the surface topology. Additionally, X-ray photoelectron spectroscopy was used to examine the chemical composition. The group demonstrated that the arrangement of atoms, nitrogen content, and electrical conductivity were all dependent on the growth conditions, particularly the temperature. Atsushi Kobayashi says that the similar structure of superconductors and semiconductors makes it easier to use superconductors in optoelectronic devices that use semiconductors.
In addition, the sharply defined interface between the AlN substrate, which has a wide bandgap, and NbNx, which is a superconductor, is required for future quantum devices such as Josephson junctions. Superconducting layers that are only a few nanometers thick and have a high level of crystallinity can be used to find single photons or electrons.
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