Physicists from the University of Southampton and ETH Zürich have reached a
new threshold of light-matter coupling at the nanoscale.
The international research, published this week in Nature Photonics,
combined theoretical and experimental findings to establish a fundamental
limitation of our ability to confine and exploit light.
The collaboration focussed on photonic nano-antennas fabricated in ever
reducing sizes on the top of a two-dimensional electron gas. The setup is
commonly used in laboratories all over the world to explore the effect of
intense electromagnetic coupling, taking advantage of the antennas' ability
to trap and focus light close to electrons.
Professor Simone De Liberato, Director of the Quantum Theory and Technology
group at the University of Southampton, says: "The fabrication of photonic
resonators able to focus light in extremely small volumes is proving a key
technology which is presently enabling advances in fields as different as
material science, optoelectronics, chemistry, quantum technologies, and many
others.
"In particular, the focussed light can be made to interact extremely
strongly with matter, making electromagnetism non-perturbative. Light can
then be used to modify the properties of the materials it interacts with,
thus becoming a powerful tool for material science. Light can be effectively
woven into novel materials."
Scientists discovered that light could no longer be confined in the system
below a critical dimension, of the order of 250nm in the sample under study,
when the experiment started exciting propagating plasmons. This caused waves
of electrons to move away from the resonator and spill the energy of the
photon.
Experiments performed in the group of Professors Jérôme Faist and Giacomo
Scalari at ETH Zürich had obtained results that could not be interpreted
with state-of-the-art understanding of light-matter coupling. The physicists
approached Southampton's School of Physics and Astronomy, where researchers
led theoretical analysis and built a novel theory able to quantitatively
reproduce the results.
Professor De Liberato believes the newfound limits could yet be exceeded by
future experiments, unlocking dramatic technological advances that hinge on
ultra-confined electromagnetic fields.
"It has been said that proofs of impossibility are only proofs of a lack of
imagination," he explains. "This is not the first time that a 'fundamental
limit' on how tightly we can focus light has been discovered. The most
famous is the Abbe diffraction limit, from 19th century German physicist
Ernst Abbe, which says light can't be confined in a volume smaller than a
cubic wavelength.
"Nanophotonics is a very active and successful field of research that is
studying different ways to break out of Abbe limit. I think the next step
will be to use some ingenuity and look for novel ways to confine light,
bypassing both Abbe limit and the one we have just discovered."
Reference:
Shima Rajabali, Erika Cortese, Mattias Beck, Simone De Liberato, Jérôme
Faist, Giacomo Scalari. Polaritonic nonlocality in light–matter interaction.
Nature Photonics, 2021;
DOI: 10.1038/s41566-021-00854-3
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Physics