Upgrading Your Computer to Quantum

Researchers at The College of Tokyo develop a nanoscale layer of a superconducting materials on prime of a nitride-semiconductor substrate, which can assist facilitate the combination of quantum qubits with present microelectronics. Credit score: Institute of Industrial Science, The College of Tokyo

Computer systems that may use quantum mechanics’ “spooky” properties to unravel issues faster than present expertise could appear interesting, however they have to first overcome a significant impediment. Scientists from Japan might have found the answer by demonstrating how a superconducting materials, niobium nitride, may be added as a flat, crystalline layer to a nitride-semiconductor substrate. This method may make it easy to fabricate quantum qubits that can be utilized with typical laptop units. 

Typical silicon microprocessor manufacturing methods have grown over many years and are frequently being refined and enhanced. Then again, the vast majority of quantum computing architectures must be created mostly from scratch. However, discovering a technique to integrate quantum and conventional logic units on a single chip, or even adding quantum capabilities to existing fabrication lines, might greatly hasten the adoption of these new systems.

Recently, a group of scientists from The University of Tokyo’s Institute of Industrial Science demonstrated how thin films of niobium nitride (NbN_x) can grow directly on top of an aluminum nitride (AlN) layer. Niobium nitride can become superconducting at temperatures colder than 16 degrees Celsius above absolute zero. Because of this, it can be utilized to create a superconducting qubit when  arranged in a structure called a Josephson junction.

The scientists investigated the impact of temperature on the crystal structures and electrical properties of NbN_x 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 because of the small lattice mismatch between aluminum nitride and niobium nitride, a highly crystalline layer could grow at the interface,” says first and corresponding author Atsushi Kobayashi.

The crystallinity of the NbN_x was characterized with X-ray diffraction, and the surface topology was captured using atomic force microscopy. In addition, the chemical composition was checked using X-ray photoelectron spectroscopy. The team showed how the arrangement of atoms, nitrogen content, and electrical conductivity all depended on the growth conditions, especially the temperature.

“The structural similarity between the two materials facilitates the integration of superconductors into semiconductor optoelectronic devices,” says Atsushi Kobayashi.

Moreover, the sharply defined interface between the AlN substrate, which has a wide bandgap, and NbN_x, which is a superconductor, is essential for future quantum devices, such as Josephson junctions. Superconducting layers that are only a few nanometers thick and have high crystallinity can be used as detectors of single photons or electrons.

Reference: “Crystal-Phase Controlled Epitaxial Growth of NbN_x Superconductors on Wide-Bandgap AlN Semiconductors” by Atsushi Kobayashi, Shunya Kihira, Takahito Takeda, Masaki Kobayashi, Takayuki Harada, Kohei Ueno and Hiroshi Fujioka, 21 September 2022, Advanced Materials Interfaces.
DOI: 10.1002/admi.202201244