Physicists and engineers have found a way to identify and address
imperfections in materials for one of the most promising technologies in
commercial quantum computing.
The University of Queensland team was able to develop treatments and
optimize fabrication protocols in common techniques for building
superconducting circuits on silicon chips.
Dr. Peter Jacobson, who co-led the research, said the team had identified
that imperfections introduced during fabrication reduced the effectiveness
of the circuits.
"Superconducting quantum circuits are attracting interest from industry
giants such as Google and IBM, but widespread application is hindered by
'decoherence', a phenomenon which causes information to be lost," he said.
"Decoherence is primarily due to interactions between the superconducting
circuit and the silicon chip—a physics problem—and to material imperfections
introduced during fabrication—an engineering problem."
"So we needed input from physicists and engineers to find a solution."
The team used a method called terahertz scanning near-field optical
microscopy (THz SNOM)—an atomic force microscope combined with a THz light
source and detector.
This provided a combination of high spatial resolution—seeing down to the
size of viruses—and local spectroscopic measurements.
Professor Aleksandar Rakić said the technique enabled probing at the
nanoscale rather than the macroscale by focusing light onto a metallic tip.
"This provides new access for us to understand where imperfections are
located so we can reduce decoherence and help reduce losses in
superconducting quantum devices," Professor Rakić said.
"We found that commonly used fabrication recipes unintentionally introduce
imperfections into the silicon chips, which contribute to decoherence."
"And we also showed that surface treatments reduce these imperfections,
which in turn reduces losses in the superconducting quantum circuits."
Associate Professor Arkady Fedorov said this allowed the team to determine
where in the process defects were introduced and optimize fabrication
protocols to address them.
"Our method allows the same device to be probed multiple times, in contrast
to other methods that often require the devices to be cut up before being
probed," Dr. Fedorov said.
"The team's results provide a path towards improving superconducting devices
for use in quantum computing applications."
In future, THz SNOM could be used to define new ways to improve the
operation of quantum devices and their integration into a viable quantum
computer.
The results are published in Applied Physics Letters.
Reference:
Xiao Guo et al, Near-field terahertz nanoscopy of coplanar microwave
resonators, Applied Physics Letters (2021).
DOI: 10.1063/5.0061078
Tags:
Physics