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| Project member Romain Tirole adjusts the equipment used in the study at Imperial College London. Credit: Thomas Angus, Imperial College London |
Imperial physicists have recreated the famous double-slit experiment, which
showed light behaving as particles and a wave, in time rather than space.
The experiment relies on materials that can change their optical properties
in fractions of a second, which could be used in new technologies or to
explore fundamental questions in physics.
The original double-slit experiment, performed in 1801 by Thomas Young at
the Royal Institution, showed that light acts as a wave. Further
experiments, however, showed that light actually behaves as both a wave and
as particles—revealing its quantum nature.
These experiments had a profound impact on quantum physics, revealing the
dual particle and wave nature of not just light, but other "particles"
including electrons, neutrons, and whole atoms.
Now, a team led by Imperial College London physicists has performed the
experiment using "slits" in time rather than space. They achieved this by
firing light through a material that changes its properties in femtoseconds
(quadrillionths of a second), only allowing light to pass through at
specific times in quick succession.
Lead researcher Professor Riccardo Sapienza, from the Department of Physics
at Imperial, said, "Our experiment reveals more about the fundamental nature
of light while serving as a stepping-stone to creating the ultimate
materials that can minutely control light in both space and time."
Details of the experiment are published today (April 3) in Nature Physics.
The original double-slit setup involved directing light at an opaque screen
with two thin parallel slits in it. Behind the screen was a detector for the
light that passed through.
To travel through the slits as a wave, light splits into two waves that go
through each slit. When these waves cross over again on the other side, they
"interfere" with each other. Where peaks of the wave meet, they enhance each
other, but where a peak and a trough meet, they cancel each other out. This
creates a striped pattern on the detector of regions of more light and less
light.
Light can also be parceled up into "particles" called photons, which can be
recorded hitting the detector one at a time, gradually building up the
striped interference pattern. Even when researchers fired just one photon at
a time, the interference pattern still emerged, as if the photon split in
two and traveled through both slits.
In the classic version of the experiment, light emerging from the physical
slits changes its direction, so the interference pattern is written in the
angular profile of the light. Instead, the time slits in the new experiment
change the frequency of the light, which alters its color. This created
colors of light that interfere with each other, enhancing and canceling out
certain colors to produce an interference-type pattern.
The material the team used was a thin film of indium-tin-oxide, which forms
most mobile phone screens. The material had its reflectance changed by
lasers on ultrafast timescales, creating the "slits" for light. The material
responded much quicker than the team expected to the laser control, varying
its reflectivity in a few femtoseconds.
The material is a metamaterial—one that is engineered to have properties not
found in nature. Such fine control of light is one of the promises of
metamaterials, and when coupled with spatial control, could create new
technologies and even analogs for studying fundamental physics phenomena
like black holes.
Co-author Professor Sir John Pendry said, "The double time slits experiment
opens the door to a whole new spectroscopy capable of resolving the temporal
structure of a light pulse on the scale of one period of the radiation."
The team next want to explore the phenomenon in a "time crystal," which is
analogous to an atomic crystal, but where the optical properties vary in
time.
Co-author Professor Stefan Maier said, "The concept of time crystals has the
potential to lead to ultrafast, parallelized optical switches."
Reference:
Romain Tirole et al, Double-slit time diffraction at optical frequencies,
Nature Physics (2023).
DOI: 10.1038/s41567-023-01993-w.
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Physics