Researchers find that fluctuations
of twisted beams of random light, such as sunlight, lead to an angular Hanbury
Brown-Twisseffect. Credit: Andreas Liapis
A
team from the University of Rochester has shown that fluctuations in
"twisted light" could be exploited for a range of applications, from
detecting rotating black holes to object detection by lidar, the
light-equivalent of radar.
In
a paper, published in Science Advances today, the researchers
demonstrate that for light from a source such as the Sun, random fluctuations
of intensity give rise to correlations of twisted
light beams. They showed the presence of these correlations by
modifying a now classical experiment called Hanbury Brown - Twiss (HBT)
interferometry to focus on the angular information contained in light, the
"twist" in the light.
The
team, from Robert W. Boyd's group at Rochester's Institute of Optics, suggest
that these correlations could allow for sunlight (or a similar type of light)
to be used for some remote sensing and object detection applications that until
now were thought to require lasers and entangled
photons.
The
new method could also offer a way to study astrophysical phenomena in which
twisted light holds a key. For example, it has been suggested that rotating black holes
could imprint a particular fingerprint in twisted light - one that could be
searched for with this new angular HBT.
"Twisted
light is all around us and occurs naturally," said Omar S. Magaña-Loaiza,
first author of the study and a Ph.D. student in Boyd's team. "And the
more random the light, the stronger the correlations of the twisted beams that
form the light. Using HBT interferometry we have been able to unveil these
correlations, which opens the door for many exciting applications."
In
1956, Robert Hanbury Brown and Richard Q. Twiss published a revolutionary
optical physics paper describing a new form of interference. Hanbury Brown and
Twiss' stellar interferometer collected light produced by two independent
sources on a star and then detected the light at two different locations on
Earth. This not only gave them an estimate of the size of Sirius with great
precision, but the HBT experiment also kicked off many discussions in the field
because it seemed that classical and quantum theories of light offered
different predictions.
The
Rochester experiment uses a similar setup but looks at twisted light. Twisted
light is light that twists as it propagates - making a sort of corkscrew shape.
It can twist more or less tightly, as described by its orbital
angular momentum. A lot of the experiments that involving twisted
light are done with lasers - coherent sources of light - and often rely on
using entangled photons. But the new experiment shows that, for many
applications, light from a star or other common sources might work just as well
as a source for twisted light.
"The
generation of entangled photons is always a complicated task," said
Magaña-Loaiza. "One of the advantages of using twisted beams of random
light is that the generation process is easier and almost natural. Another
advantage is that standard detectors can be used instead of single photon
detectors. This is important because scientists would not be limited to work at
low-light levels, which opens the door for some real-life applications.
Typically the use of entangled photons forces scientists to work in darkness,
otherwise, noise severely affects experiments."
But
Magaña-Loaiza is clear that correlations in twisted light do not offer an
alternative for many other applications that require entangled photons. He
added that "entangled photons offer other attributes that random fields of
light do not provide, for example perfect correlations
and non-locality, both quantum effects."
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