Researchers used lasers to recreate the well-known double slit experiment,
but their slits are in time rather than space.
For the first time, researchers have demonstrated the ability to send light
through "slits" in time.
In the new experiment, light is shone through two slits in a screen to
produce a novel diffraction pattern over space, where the peaks and troughs
of the light wave add up or cancel out. This experiment updates a
demonstration that dates back 240 years. In the latest work, scientists
produced a comparable temporal pattern, basically altering the hue of an
ultrashort laser pulse.
The discoveries open the door to improvements in analog computers, which
manage data encoded on light beams rather than digital bits; they may even
enable such computers to "learn" from the data. Additionally, they enhance
our comprehension of the fundamental properties of light and how it
interacts with various materials.
Indium tin oxide (ITO), the substance used in the majority of phone
screens, was employed in the new study, which was published on April 3 in
the journal
Nature Physics. ITO can transition from transparent to reflective in reaction to light,
as scientists already knew, but the researchers discovered it happens far
more quickly than previously believed—in less than 10 femtoseconds. (10
millionths of a billionth of a second).
Riccardo Sapienza, a physicist at Imperial College London and the study's principal author,
told Live Science, "This was a really huge surprise and at the beginning it
was something that we couldn't understand. By carefully examining the idea
of how the electrons in ITO react to incoming light, the researchers
eventually discovered why the reaction occurred so quickly. But it took us a
while to figure it out.
changing space for time
In 1801 English physicist Thomas Young used the now-famous "double-slit"
experiment to show that light behaves like a wave. The waves on a screen
with two slits change direction when light shines on it, causing the waves
coming through one slit to fan out and cross over the waves coming through
the other. An interference pattern is produced when the peaks and troughs of
these waves either add up or cancel out, producing brilliant and dark
fringes.
In the latest research, Sapienza and associates used an ITO-coated screen
and a "pump" laser pulse to simulate an interference pattern over time.
Although the ITO was initially clear, the laser's light caused the electrons
there to change their characteristics, making the material reflect light
like a mirror. This momentary alteration in the optical characteristics
would then be seen as a few hundred femtosecond-long slit in time by a
subsequent "probe" laser beam striking the ITO screen. The material behaved
as though it had two time-dependent slits, simulating light traveling
through spatial double slits, when a second pump laser pulse was
applied.
When light travelled through these twin "time slits," it varied in
frequency, which is inversely proportional to its wavelength, as opposed to
traveling through ordinary spatial slits, which cause light to shift
direction and fan out. The color of visible light is determined by its
wavelength.
Fringes or extra peaks in the frequency spectra, which are graphs of the
observed light intensity at various frequencies, appeared in the new
experiment as the interference pattern. The spacing of the interference
fringes in the frequency spectra is determined by the lag between the
temporal slits, just as changing the distance between spatial slits alters
the interference pattern that results. It also tells how rapidly the ITO
characteristics are changing by how many fringes in these interference
patterns can be seen before their amplitude drops to background noise;
materials with slower responses produce fewer discernible interference
fringes.
It's not the first time that researchers have discovered a way to control
light through time rather than just space. In contrast to atoms being
organized in a periodic pattern throughout space, Google scientists claim
that their quantum computer "Sycamore" developed a time crystal, a new phase
of matter that changes regularly in time.
A physicist at The City University of New York named Andrea Alù(opens in
new tab), who was not engaged in these tests but has carried out other
investigations that resulted in light reflections in time, called it yet
another "neat demonstration" of how time and space may be
interchangeable.
Alù told Live Science via email that the experiment's most surprising
feature is how it shows how we can quickly and significantly change the
material (ITO)'s permittivity, which describes how much a material transmits
or reflects light. This demonstrates that this substance is a prime
candidate for showing time reflections and time crystals.
The goal of the research is to develop metamaterials—structures made to
specifically and frequently intricately modify the course of light—using
these phenomena.
As of until, these metamaterials have remained static, necessitating the
use of a whole new metamaterial structure, such as a new analog computer for
each distinct sort of calculation, according to Sapienza.
"Now that we have a material that we can reconfigure, we can use it for
multiple purposes," Sapienza added. He continued by saying that such
technology may allow for brain-like neuromorphic computing.
