Friday, May 20, 2022

Stopping light for tiny fractions of a second

Can you stop the world’s fastest thing, i.e., light? Of course, no one can.

But, scientists from the Technische Universitat Darmstadt are trying to do the impossible: stopping light for tiny fractions of a second.

Scientists still used light sources to emit individual photons, process the information stored on light particles, it would also be necessary for single photons to interact, which they do not usually do. Light particles also have a pivotal role in future quantum computer technology.

To this end as well, the cooperation between the two types of particles must be intensified, which the photons halted by the gathering from the TU Darmstadt could make conceivable.

For quite a while, it has been conceivable to freeze photons and re-produce them on order. Be that as it may, while they are stopped, the photons don’t exist as it is. They are gulped by an atomic cloud, which is assumed as a purported energized so-called excited state and stores the photon as information. Endless supply of a sign does the excitation change back into a photon, which at that point forges ahead.

Scientists in Darmstadt are doing it in the same manner, yet with one crucial difference: their photons are preserved.

The light stands still. Using a unique glass fiber with a hollow channel in the center with a diameter of fewer than ten-thousandths of a millimeter. The fiber has a porous structure around the core that keeps light at bay. This causes a laser beam to concentrate in the center of the hollow channel. Its cross-section narrows to around one-thousandth of a millimeter.

Scientists then used a light beam as a kind of trap for atoms. They introduce atoms of rubidium into the hollow fiber, which concentrates in the center of the laser beam due to electromagnetic forces.

They then sent photons they want to stop into the channel. And surprisingly, the photons are stopped by two additional laser beams that are guided into the hollow fiber on both sides.

Dr. Thorsten Peters explains, “It is also similar to a chamber in which light is thrown back and forth between two mirrors. Just without a mirror.”

“We are first to succeed in slowing down photons in such a narrow capillary in this way, and it was not easy. It is made extremely complicated by an optical property known as birefringence. The team was able to refine their method through a laborious birefringence analysis to the point where stopping individual photons became possible.”

“But simply stopping light itself they did not satisfy themselves. Our objective was to make photons interact with atoms more strongly than they normally do. In particular, it should be possible for two light particles to interact with an atom at the same time, which would produce a useful phenomenon known in physics as nonlinear optics in which photons penetrate a medium, such as a special crystal. When two photons simultaneously strike one of the atoms in the crystal, they interact with one another, which changes the frequency, i.e., the color of the light. The new frequency could, for example, be the sum of the frequencies of the photons that are sent in.”

“With our method, on the other hand, the weak light intensity may be sufficient.” This is possible because the atoms are confined to the same narrow area as the laser beam within the hollow fiber, thus maximizing the contact between the light and the atomic cloud. Therefore the probability of two photons hitting an atom simultaneously is relatively high even when the light intensity is low. So the same technical trick that makes it possible to stop the photons should also create a new method for nonlinear optics.”

“We are continuing to work intensively on this.”

Journal Reference:
  1. Thorsten Peters et al. Single-photon-level narrowband memory in a hollow-core photonic bandgap fiber. DOI: 10.1364/OE.383999


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