Researchers at the University of Bath in the UK have found a way to make
'single-crystal flake' devices that are so thin and free of defects, they
have the potential to outperform components used today in quantum computer
circuits.
The study is published this month in the journal Nano Letters.
The team from the university's Department of Physics made its discovery
while exploring the junction between two layers of the superconductor
niobium diselenide (NbSe2) after these layers had been cleaved apart,
twisted about 30 degrees with respect to one another, then stamped back
together. In cleaving, twisting and recombining the two layers, the
researchers were able to build a Superconducting Quantum Interferometer
Device (SQUID) – an extremely sensitive sensor used to measure incredibly
tiny magnetic fields.
SQUIDs have a wide range of important applications in areas that include
healthcare (as seen in cardiology and magnetoencephalography—a test that
maps brain function) and mineral exploration.
SQUIDS are also the building blocks of today's commercial quantum
computers—machines that perform certain computational tasks much more
rapidly than classical computers. Quantum computing is still in its infancy
but in the next decade, it is likely to transform the problem-solving
capacity of companies and organizations across many sectors—for instance by
fast-tracking the discovery of new drugs and materials.
"Due to their atomically perfect surfaces, which are almost entirely free of
defects, we see potential for our crystalline flakes to play a significant
role in building quantum computers of the future," said Professor Simon
Bending, who carried out the research together with his Ph.D. student Liam
Farrar. "Also, SQUIDs are ideal for studies in biology—for instance, they
are now being used to trace the path of magnetically-labeled drugs through
the intestine—so we're very excited to see how our devices could be
developed in this field too."
As Professor Bending is quick to point out, however, his work on SQUIDs made
using NbSe2 flakes is very much at the start of its journey. "This is a
completely new and unexplored approach to making SQUIDs and a lot of
research will still have to done before these applications become a
reality," he said.
Extremely thin single crystals
The flakes from which the Bath superconductors are fabricated are extremely
thin single crystals (10,000 times thinner than a human hair) that bend
easily, which also makes them suitable for incorporation into flexible
electronics, as used in computer keyboards, optical displays, solar cells
and various automotive components.
Because the bonds between layers of NbSe2 are so weak, cleaved flakes—with
their perfectly flat, defect-free surfaces—create atomically sharp
interfaces when pushed back together again. This makes them excellent
candidates for the components used in quantum computing.
While this is not the first time NbSe2 layers have been stamped together to
create a weak superconducting link, this is the first demonstration of
quantum interference between two such junctions patterned in a pair of
twisted flakes. This quantum interference has allowed the researchers to
modulate the maximum supercurrent that can flow through their SQUIDs by
applying a small magnetic field, creating an extremely sensitive field
sensor. They were also able to show that the properties of their devices
could be systematically tuned by varying the twist angle between the two
flakes.
Reference:
Liam S. Farrar et al, Superconducting Quantum Interference in Twisted van
der Waals Heterostructures, Nano Letters (2021).
DOI: 10.1021/acs.nanolett.1c00152
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