In Einstein's footsteps and beyond
Zero-index metamaterials offers new insights into the foundations of
quantum mechanics
Date:
April 27, 2022
Source:
Harvard John A. Paulson School of Engineering and Applied Sciences
Summary:
Physicists are re-examining the foundations of quantum physics
from the perspective of momentum and exploring what happens when
the momentum of light is reduced to zero.
FULL STORY ==========================================================================
In physics, as in life, it's always good to look at things from different perspectives.
========================================================================== Since the beginning of quantum physics, how light moves and interacts with matter around it has mostly been described and understood mathematically through the lens of its energy. In 1900, Max Planck used energy to
explain how light is emitted by heated objects, a seminal study in the foundation of quantum mechanics. In 1905, Albert Einstein used energy
when he introduced the concept of photon.
But light has another, equally important quality known as momentum. And,
as it turns out, when you take momentum away, light starts behaving in
really interesting ways.
An international team of physicists led by Michae"l Lobet, a research
associate at the Harvard John A. Paulson School of Engineering and
Applied Sciences (SEAS) and Eric Mazur, the Balkanski Professor of
Physics and Applied Physics at SEAS, are re-examining the foundations
of quantum physics from the perspective of momentum and exploring what
happens when the momentum of light is reduced to zero.
The research is published inNature Light Science & Applications.
Any object with mass and velocity has momentum -- from atoms to bullets to asteroids -- and momentum can be transferred from one object to another. A
gun recoils when a bullet is fired because the momentum of the bullet is transferred to the gun. At the microscopic scale, an atom recoils when it
emits light because of the acquired momentum of the photon. Atomic recoil, first described by Einstein when he was writing the quantum theory of radiation, is a fundamental phenomenon which governs light emission.
==========================================================================
But a century after Planck and Einstein, a new class of metamaterials
is raising questions regarding these fundamental phenomena. These
metamaterials have a refractive index close to zero, meaning that when
light travels through them, it doesn't travel like a wave in phases of
crests and troughs. Instead, the wave is stretched out to infinity,
creating a constant phase. When that happens, many of the typical
processes of quantum mechanics disappear, including atomic recoil.
Why? It all goes back to momentum. In these so-called near-zero index materials, the wave momentum of light becomes zero and when the wave
momentum is zero, odd things happen.
"Fundamental radiative processes are inhibited in three dimensional
near-zero index materials," says Lobet, who is currently a lecturer at the University of Namur in Belgium. "We realized that the momentum recoil of
an atom is forbidden in near-zero index materials and that no momentum
transfer is allowed between the electromagnetic field and the atom."
If breaking one of Einstein's rules wasn't enough, the researchers
also broke perhaps the most well-known experiment in quantum physics --
Young's double- slit experiment. This experiment is used in classrooms
across the globe to demonstrate the particle-wave duality in quantum
physics -- showing that light can display characteristics of both waves
and particles.
In a typical material, light passing through two slits produces two
coherent sources of waves that interfere to form a bright spot in the
center of the screen with a pattern of light and dark fringes on either
side, known as diffraction fringes.
========================================================================== "When we modelled and numerically computed Young's double-slit experiment,
it turned out that the diffraction fringes vanished when the refractive
index was lowered," said co-author Larissa Vertchenko, of the Technical University of Denmark.
"As it can be seen, this work interrogates fundamental laws of quantum mechanics and probes the limits of wave-corpuscle duality," said co-author In~igo Liberal, of the Public University of Navarre in Pamplona, Spain.
While some fundamental processes are inhibited in near-zero refractive
index materials, others are enhanced. Take another famous quantum
phenomenon - - Heisenberg's uncertainty principle, more accurately known
in physics as the Heisenberg inequality. This principle states that
you cannot know both the position and speed of a particle with perfect
accuracy and the more you know about one, the less you know about the
other. But, in near-zero index materials, you know with 100% certainty
that the momentum of a particle is zero, which means you have absolutely
no idea where in the material the particle is at any given moment.
"This material would make a really poor microscope, but it does enable
to cloak objects quite perfectly," Lobet said. "In some way, objects
become invisible." "These new theoretical results shed new light on
near-zero refractive index photonics from a momentum perspective,"
said Mazur. "It provides insights in the understanding of light-matter interactions in systems with a low- refraction index, which can be useful
for lasing and quantum optics applications." The research could also
shed light on other applications, including quantum computing, light
sources that emit a single photon at a time, the lossless propagation
of light through a waveguide and more.
The team next aims to revisit other foundational quantum experiments
in these materials from a momentum perspective. Afterall, even
though Einstein didn't predict near-zero refractive index materials,
he did stress the importance of momentum. In his seminal 1916 paper
on fundamental radiative processes, Einstein insisted that, from a
theoretical point of view, energy and momentum "should be considered on
a completely equal footing since energy and momentum are linked in the
closest possible way." "As physicists, it's a dream to follow in the
footsteps of giants like Einstein and push their ideas further," said
Lobet. "We hope that we can provide a new tool that physicists can use
and a new perspective, which might help us understand these fundamental processes and develop new applications."
========================================================================== Story Source: Materials provided by Harvard_John_A._Paulson_School_of_Engineering_and_Applied
Sciences. Original written by Leah Burrows. Note: Content may be edited
for style and length.
========================================================================== Related Multimedia:
* Illustration_of_a_near-zero_index_metamaterial ========================================================================== Journal Reference:
1. Michae"l Lobet, In~igo Liberal, Larissa Vertchenko, Andrei
V. Lavrinenko,
Nader Engheta, Eric Mazur. Momentum considerations inside near-zero
index materials. Light: Science & Applications, 2022; 11 (1) DOI:
10.1038/ s41377-022-00790-z ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220427154106.htm
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