Image illustrating sound frequency with light

A new mechanism has been discovered that controls the flow of sound

The influence of the magnetic field on electrons has a wide impact. This could lead to many unique phenomena in the materials. For many applications, it would be useful if the same could be achieved for vibration and sound waves. Scientists have long wanted to know if a sound that has no charge can achieve a magnetic field-like effect on electrons.

In a new study, AMOLF researchers used a network of vibrating light-controlled nano-strings to control the flow of sound. For the first time, they were able to cause sound waves to move in a certain irreversible direction and weaken or amplify them in a controlled manner. This creates a laser effect for the sound.

Surprisingly, scientists have come up with new mechanisms called “geometric phases.” This mechanism allowed them to control and transmit sound in systems that were considered impossible.

Group leader Ewold Verhagen said: “This paves the way for new types of (meta) materials with properties we don’t yet know from existing materials.”

Magnetic field for sound

Because mechanical vibrations have no charge, they do not respond to magnetic fields. However, they are sensitive to the radiation pressure of light.

The researchers therefore used laser light to affect the mechanical nano-resonators.

Verhagen said “We have now shown that if we create a network of more vibrating nano-strings, we can realize a number of unconventional vibration patterns by illuminating the strings with laser light. For example, we managed to get sound particles (phonons) to move in one direction in the same way as electrons in the quantum Hall effect. ”

The researchers also realized that radiation pressure could also be used to control sound amplification and attenuation.

Verhagen said “Such amplification or attenuation is impossible for electrons in a magnetic field.”

Scientists are the first to conduct experiments in which driving light amplifies sound waves while ensuring that they are exposed to a magnetic field-like effect.

Verhagen said “We have found that amplifying and breaking the symmetry of time reversal leads to a number of new and unexpected physical effects. Laser light primarily determines the direction in which the sound is amplified. In the opposite direction, the sound is blocked. This is due to the geometric phase: a quantity that indicates the extent to which the sound wave is displaced as it passes through the nano-string network, which in this case is caused by the radiation pressure. ”

“Our experiment allowed us to fully control and change this geometric phase. In addition, we used laser light pressure to amplify the sound. The sound can even oscillate spontaneously, like light in a laser. We have found that the geometric phase we apply determines whether this happens or not, and with what strength of amplification.

“We have found that new geometric phases can be implemented in systems where this was not considered possible. In all these phases, they affect the amplification, direction and pitch of the sound waves. “

“Geometric phases are important in many branches of physics, they describe the behavior of different systems and materials. In combination with magnetic fields, they can lead to a topological insulator for electrons, but we still have to learn what properties a “sound” variant based on the discovered principles could have. But we know it won’t be like anything we know. “

“We could further investigate the effects by connecting multiple nano-strings in acoustic ‘metamaterials’ that we control with light. But the effects we have observed should apply to a number of uncharged waves, including light, microwaves, cold atoms, etc. We expect that with the new mechanisms we have discovered, it will be possible to produce new (meta) materials with properties that have so far we do not know about existing materials. “

“Such materials and systems have unusual properties that could have useful applications. It is still too early to see the full possibilities. However, we can already identify some potential directions. For example, a DC amplifier for waves could have useful applications in quantum communication. We could also make the sensors much more sensitive by breaking the symmetry of the reversal of time. “

Magazine link:

  1. Javier del Pino, Jesse J. Slim, Ewold Verhagen, Non-Hermitian chiral phononics through optomechanically induced squeezing, Nature, June 2 (2022). DOI: 10.1038 / s41586-022-04609-0

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