|
|
Artist's impression of how photons bound together after interaction
with artificial atom. Credit: The University of Basel
|
For the first time, scientists at the University of Sydney and the
University of Basel in Switzerland have demonstrated the ability to
manipulate and identify small numbers of interacting photons—packets of
light energy—with high correlation.
This unprecedented achievement represents an important landmark in the
development of quantum technologies. It is published today in Nature
Physics.
Stimulated light emission, postulated by Einstein in 1916, is widely
observed for large numbers of photons and laid the basis for the invention
of the laser. With this research, stimulated emission has now been observed
for single photons.
Specifically, the scientists could measure the direct time delay between one
photon and a pair of bound photons scattering off a single quantum dot, a
type of artificially created atom.
"This opens the door to the manipulation of what we can call 'quantum
light'," Dr. Sahand Mahmoodian from the University of Sydney School of
Physics and joint lead author of the research said.
Dr. Mahmoodian said, "This fundamental science opens the pathway for
advances in quantum-enhanced measurement techniques and photonic quantum
computing."
By observing how light interacted with matter more than a century ago,
scientists discovered light was not a beam of particles, nor a wave pattern
of energy—but exhibited both characteristics, known as wave-particle
duality.
The way light interacts with matter continues to enthrall scientists and the
human imagination, both for its theoretical beauty and its powerful
practical application.
Whether it be how light traverses the vast spaces of the interstellar medium
or the development of the laser, research into light is a vital science with
important practical uses. Without these theoretical underpinnings,
practically all modern technology would be impossible. No mobile phones, no
global communication network, no computers, no GPS, no modern medical
imaging.
One advantage of using light in communication—through optic fibers—is that
packets of light energy, photons, do not easily interact with each other.
This creates near distortion-free transfer of information at light speed.
However, we sometimes want light to interact. And here, things get tricky.
For instance, light is used to measure small changes in distance using
instruments called interferometers. These measuring tools are now
commonplace, whether it be in advanced medical imaging, for important but
perhaps more prosaic tasks like performing quality control on milk, or in
the form of sophisticated instruments such as LIGO, which first measured
gravitational waves in 2015.
The laws of quantum mechanics set limits as to the sensitivity of such
devices.
This limit is set between how sensitive a measurement can be and the average
number of photons in the measuring device. For classical laser light this is
different to quantum light.
Joint lead author, Dr. Natasha Tomm from the University of Basel, said, "The
device we built induced such strong interactions between photons that we
were able to observe the difference between one photon interacting with it
compared to two."
"We observed that one photon was delayed by a longer time compared to two
photons. With this really strong photon-photon interaction, the two photons
become entangled in the form of what is called a two-photon bound state."
Quantum light like this has an advantage in that it can, in principle, make
more sensitive measurements with better resolution using fewer photons. This
can be important for applications in biological microscopy when large light
intensities can damage samples and where the features to be observed are
particularly small.
"By demonstrating that we can identify and manipulate photon-bound states,
we have taken a vital first step towards harnessing quantum light for
practical use," Dr. Mahmoodian said.
"The next steps in my research are to see how this approach can be used to
generate states of light that are useful for fault-tolerant quantum
computing, which is being pursued by multimillion dollar companies, such as
PsiQuantum and Xanadu."
Dr. Tomm said, "This experiment is beautiful, not only because it validates
a fundamental effect—stimulated emission—at its ultimate limit, but it also
represents a huge technological step towards advanced applications."
"We can apply the same principles to develop more-efficient devices that
give us photon bound states. This is very promising for applications in a
wide range of areas: from biology to advanced manufacturing and quantum
information processing."
The research was a collaboration between the University of Basel, Leibniz
University Hannover, the University of Sydney and Ruhr University Bochum.
The lead authors are Dr. Natasha Tomm from the University of Basel and Dr.
Sahand Mahmoodian at the University of Sydney, where he is an Australian
Research Council Future Fellow and Senior Lecturer.
The artificial atoms (quantum dots) were fabricated at Bochum and used in
experiment performed in the Nano-Photonics Group at the University of Basel.
Theoretical work on the discovery was carried out by Dr. Mahmoodian at the
University of Sydney and Leibniz University Hannover.
Reference:
Natasha Tomm, Photon bound state dynamics from a single artificial atom,
Nature Physics (2023).
DOI: 10.1038/s41567-023-01997-6.