Einstein's Footprints and Beyond

Einstein's Footprints and Beyond
A drawing of a near-zero index metamaterial shows that light moves in a stationary phase when it passes through it. Credits: Second Bay Studios/Harvard SEAS

Since the beginning of quantum physics, the movement and interaction of light with matter has been mathematically defined and comprehended predominantly through the lens of its energy. In a groundbreaking work in the foundations of quantum physics, Max Planck used energy in 1900 to explain how light emanates from heated objects. When Albert Einstein created the concept of the photon in 1905, he used energy. It also emerges that attention should be paid to Einstein's Footprints and Beyond while proposing New Views on the Fundamentals of Quantum Mechanics.

However, light has another essential property known as momentum. And as it turns out, when you get the momentum, the light starts behaving in really unusual ways. A multinational group of physicists is re-examining the foundations of quantum physics in terms of momentum and investigating what happens when the momentum of light is reduced to zero. The team is led by Michael Lobet, a research associate at Harvard's John A. Paulson School of Engineering and Applied Sciences (SEAS), and Eric Mazur, Balkanski Professor of Physics and Applied Physics at SEAS.

On April 25, 2022, the findings were published in the journal Nature Light Science & Applications.

From atoms to bullets and asteroids, every object with mass and velocity has momentum, and momentum can be transmitted from one object to another. When a bullet fires, the gun recoils because the momentum of the bullet is transferred to the gun. When an atom produces light due to the momentum gained by the photon, it rebounds on a microscopic scale. Atomic recoil is a fundamental phenomenon that governs light emission, originally described by Einstein when he created the quantum theory of radiation.

However, a century after Planck and Einstein, a new class of metamaterials raises questions about these fundamental phenomena. These metamaterials have a near-zero index of refraction, meaning that light does not flow through them in crest and trough waves. Instead, the wave is stretched to infinity, resulting in a stationary phase. Many common quantum physics phenomena, such as atomic kickback, disappear when this happens.

Why everything goes back to momentum. In these near-zero index materials, the wave momentum of light becomes zero, and strange things happen when the wave momentum is zero.

“Basic radiative processes are inhibited in three-dimensional near-zero index materials,” explains Lobet, a lecturer at Namur University in Belgium. “We discovered that the momentum recoil of an atom is forbidden in materials with near zero indexes, and that no momentum transfer is allowed between the electromagnetic field and the atom.”

If violating one of Einstein's principles wasn't enough, the researchers also destroyed Young's double-slit experiment, which is probably the best-known quantum physics experiment. This experiment is used in classrooms around the world to explain the particle-wave duality of quantum physics, which shows that light can have both wave and particle properties.

Light flowing through two slits in a standard material produces two coherent wave sources that interact to form a bright spot in the center of the screen; these form a pattern of light and dark fringes on both sides, known as diffraction fringes.


Light Double Slit Experiment
In the double slit experiment, light passing through the two slits produces two coherent wave sources that interfere with creating a bright spot in the middle of the screen with a pattern of light and dark fringes known as diffraction fringes. Credits: Harvard John A. Paulson School of Engineering and Applied Sciences

"When we modeled and numerically analyzed Young's double-slit experiment, we discovered that when the refractive index decreased, the diffraction fringes disappeared," said co-author Larissa Vertchenko of the Technical University of Denmark.
"As can be observed, this work explores the limits of wave-particle duality and questions the fundamental laws of quantum physics," said co-author Iñigo Liberal of Navarre State University in Pamplona, ​​Spain.

Some basic operations are inhibited, while others are facilitated in materials with near-zero refractive index. Another well-known quantum phenomenon is Heisenberg's uncertainty principle, sometimes known in physics as the Heisenberg inequality. This concept asserts that you cannot know both the position and velocity of a particle exactly, and that the more you know about one, the less you know about the other. However, in materials with an index close to zero, you can be sure that the momentum of the particle is zero, meaning you have no idea where the particle is in the material at any given time.

“This material makes a terrible microscope,” Lobet said, “but it lets you hide objects completely.” “Objects somehow become invisible.”

“From a momentum perspective, these new theoretical results offer new insights into near-zero refractive index photonics,” Mazur added. “It contributes to our understanding of light-matter interactions in low-refractive index systems, which is useful for lasing and quantum optics applications.”

Other applications of the research could include quantum computers, light sources that emit a single photon at a time, lossless light propagation through a waveguide, and more.

From a momentum perspective, the team plans to examine other fundamental quantum experiments in these materials. Even though Einstein did not predict materials with near-zero refractive index, he stressed the importance of momentum. In his important work on fundamental radiative processes in 1916, Einstein wrote that "since energy and momentum are related in the closest possible way, they must be viewed on an entirely equal basis from a theoretical point of view".

“As physicists, it is a dream to follow in the footsteps of geniuses like Einstein and push their theories further,” Lobet added. “We aim to equip physicists with a new tool and a new perspective to help us better understand these fundamental processes and develop new applications.”

source: scitechdaily

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