Light
has the properties of both a particle and a wave. Scientists have been
attempting to directly detect both of these characteristics of light at the
same time since Einstein's time. EPFL scientists have now managed to capture
the first-ever image of this dual activity.
According
to quantum theory, light can act as both a particle and a wave at the same
time. However, no experiment has ever been able to catch both the wave and
particle natures of light at the same time; the closest we've come is seeing
either wave or particle at various moments. EPFL scientists have taken the
first ever photo of light acting both as a wave and as a particle using a
totally different experimental approach. Nature Communications released the ground-breaking
research.
When
UV light strikes a metal surface, electrons are emitted. This
"photoelectric" effect was explained by Albert Einstein, who proposed
that light, which was previously assumed to be merely a wave, is also a stream
of particles. Despite the fact that numerous experiments have successfully
detected both the particle- and wave-like properties of light, no experiment
has ever been able to witness both at the same time.
EPFL
researchers lead by Fabrizio Carbone have recently completed an experiment in
which electrons were used to photograph light. For the first time, the
researchers have captured a single photo of light acting as both a wave and a
stream of particles at the same moment.
The
setup for the experiment is as follows: a laser pulse is shot at a tiny
metallic nanowire. The laser causes the charged particles in the nanowire to
vibrate by adding energy to them. Like cars on a motorway, light moves in two
directions along this little wire. When waves going in opposite directions
collide, they generate a new wave that appears to be stationary. This standing
wave now serves as the experiment's light source, propagating around the
nanowire.
This
is where the gimmick of the experiment comes into play: The researchers used a
stream of electrons to scan the standing wave of light by shooting them near to
the nanowire. The electrons either sped up or slowed down as they interacted
with the confined light on the nanowire. Carbone's team was able to visualise
the standing wave, which functions as a fingerprint of the wave-nature of
light, by using an ultrafast microscope to scan the location where this shift
in speed happened.
While
this phenomenon demonstrates light's wave-like nature, it also demonstrates its
particle nature. The electrons "strike" the light's particles, the
photons, as they pass close to the standing wave of light. As previously
stated, this has an impact on their speed, causing them to go quicker or
slower. The exchange of energy "packets" (quanta) between electrons
and photons causes the change in speed. The presence of these energy packets
demonstrates that light on a nanowire behaves like a particle.
"This
experiment reveals that we can record quantum physics – and its paradoxical
character – directly for the first time ever," explains Fabrizio Carbone.
Furthermore, the significance of this ground-breaking finding extends beyond
fundamental research to future technology. "Being able to view and manipulate
quantum processes at the nanoscale scale opens up a new route towards quantum
computing," says Carbone.
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