Researchers exploring the
interactions between light particles, photons and matter find that optical
microresonators host quasiparticles made by two photons.
From:
University of Bath
March
2, 2021 -- Scientists at the University of Bath have found a way to bind
together two photons of different colors, paving the way for important
advancements in quantum-electrodynamics – the field of science that describes
how light and matter interact. In time, the team’s findings are likely to
impact developments in optical and quantum communication, and precision
measurements of frequency, time and distances.
Apple and
wave: they both have a mass
An apple falling from a tree has
velocity and mass, which together give it momentum. ‘Apple energy’ derived from
motion depends on the fruit’s momentum and mass.
Most people find the concept of momentum
and energy (and therefore mass) an easy one to grasp when it’s associated with
solid objects. But the idea that non-material objects, such as light waves
(everything from sunlight to laser radiation), also have a mass is surprising
to many. Among physicists, however, it’s a well-known fact. This apparently
paradoxical idea that waves have a mass marks the place where quantum physics
and the physical world come together.
The wave-particle duality, proposed by
French physicist Louis de Broglie in 1924, is a powerful concept that describes
how every particle or quantum entity can be described as either a particle or a
wave. Many so-called quasiparticles have been discovered that combine either
two different types of matter particles, or light waves bound to a particle of
matter. A list of exotic quasiparticles includes phonons, plasmons, magnons and
polaritons.
The team of physicists at Bath has now
reported a way to create quasiparticles that bind together two differently colored
particles of light. They have named these formations photon-photon polaritons.
Detecting
photon-photon polaritons
The opportunity to discover, and
manipulate, photon-photons is possible thanks to the relatively new development
of high-quality microresonators. For light, microresonators act as miniature
racetracks, with photons zipping around the internal structure in loops. The
signature left by photon-photons in the light exiting the microresonator can be
linked to the Autler–Townes effect, a peculiar phenomenon in quantum theory
that describes strong photon-atom interactions. To achieve this effect in
microresonators, a laser is tuned to the specific resonance frequency where a
photon is expected to be absorbed, yet no resonance absorption happens.
Instead, the photon-photon interaction makes up two new resonance frequencies
away from the old one.
A significant feature that has emerged
from the Bath research is that the microresonator provided a whole set of split
resonances, where each photon-photon pair displayed its own momentum and
energy, allowing the researchers to apply the quasiparticle concept and
calculate mass. According to the researchers’ predictions, photon-photons are
1,000+ times lighter than electrons.
Professor Dmitry Skryabin, the physicist
who led the research, said: "We now have a situation where microresonators
– which are millimeter-scale objects – behave like giant atoms. The artificial
atoms concept is rapidly gaining ground in the quantum-electrodynamics of
microwaves in superconducting circuits, while here we are looking at the
similar opportunity in the optical range of frequencies.
“The small mass of photon-photons could
lead to further developments of many important analogies between light and
fluids, where other families of quasiparticles have already been used."
PhD student Vlad Pankratov, who
participated in the project, said: “After a year of running models and
collecting data, these are incredibly exciting findings for us. The potential
applications of our results are in the terabit and quantum optical
communication schemes, and in the area of precision measurements."
This work was supported by the European
Union Marie Skłodowska-Curie Actions (812818, MICROCOMB)
The paper Photon-photon
polaritons in χ(2) microresonators is published in Physical Review
Research.
= = = = = = = = = = = = = = = = = = = =
= = = = = = = = = = = = = = =
An optical microcavity or microresonator is
a structure formed by reflecting faces on the two sides of a spacer layer or
optical medium, or by wrapping a waveguide in a circular fashion to form
a ring. The former type is a standing
wave cavity, and the latter is a traveling
wave cavity. The name microcavity stems from the fact that
it is often only a few micrometers thick, the spacer layer sometimes even in
the nanometer range. As with common lasers this
forms an optical cavity or optical resonator,
allowing a standing wave to form inside the spacer layer,
or a traveling wave that goes around in the ring.
https://en.wikipedia.org/wiki/Optical_microcavity
No comments:
Post a Comment