Topological insulators are materials whose structure forces photons and
electrons to move only along the material's boundary and only in one
direction. These particles experience little resistance and travel freely
past obstacles such as impurities, fabrication defects, a change of signal's
trajectory within a circuit, or objects placed intentionally in the
particles' path. That's because these particles, instead of being reflected
by the obstacle, go around it "like river-water flowing past a rock," says
Prof. Romain Fleury, head of EPFL's Laboratory of Wave Engineering, within
the School of Engineering.
Until now, these particles' exceptional resilience to obstacles applied only
to limited perturbations in the material, meaning this property couldn't be
exploited widely in photonics-based applications. However, that could soon
change thanks to research being conducted by Prof. Fleury along with his
Ph.D. student Zhe Zhang and Pierre Delplace from the ENS Lyon Physics
Laboratory. Their study, appearing in the journal Nature, introduces a
topological insulator in which the transmission of microwave photons can
survive unprecedented levels of disorder.
"We were able to create a rare topological phase that can be characterized
as an anomalous topological insulator. This phase arises from the
mathematical properties of unitary groups and gives the material unique—and
unexpected—transmission properties," says Zhang.
This discovery holds great promise for new advances in science and
technology. "When engineers design hyperfrequency circuits, they have to be
very careful to make sure that waves are not reflected but rather guided
along a given path and through a series of components. That's the first
thing I teach my electrical engineering students," says Prof. Fleury. "This
intrinsic constraint, known as impedance matching, limits our ability to
manipulate wave signals. However, with our discovery, we can take a
completely different approach, by using topology to build circuits and
devices without having to worry about impedance matching—a factor that
currently restricts the scope of modern technology."
Prof. Fleury's lab is now working on concrete applications for their new
topological insulator. "These types of topological circuits could be
extremely useful for developing next-generation communication systems," he
says. "Such systems require circuits that are highly reliable and easily
reconfigurable." His research group is also looking at how the discovery
could be used for developing new kinds of photonic processors and quantum
computers.
Reference:
Romain Fleury, Superior robustness of anomalous non-reciprocal topological
edge states, Nature (2021).
DOI: 10.1038/s41586-021-03868-7.
Tags:
Physics