In a network of vibrating nanochords, the radiation pressure of the laser light causes sound waves to travel in one direction across the network and amplify the vibrations at the same time. Credit: Ricardo Struik (AMOLF)
Using a network of light-controlled vibrating nano-strings, AMOLF researchers have caused sound waves to move in a specific irreversible direction and have attenuated or amplified the waves in a controlled way for the first time. This results in a laser effect for the sound. To their surprise, they discovered new mechanisms, the so-called “geometric phases”, with which they can manipulate and transmit sound in systems where this was thought impossible. “This paves the way for new types of (meta) materials with properties we don’t yet know about existing materials,” says group leader Ewold Verhagen, who, along with leading authors Javier del Pino and Jesse Slim, publishes amazing results. on June 2 a Nature.
The response of electrons and other charged particles to magnetic fields leads to many unique phenomena in materials. “For a long time, we wanted to know if a similar effect could be achieved on a magnetic field on electrons on sound, which has no charge,” says Verhagen. “The influence of a magnetic field on electrons has a wide impact: for example, an electron in a magnetic field cannot move in the same direction in the opposite direction. This principle is at the basis of various exotic phenomena at the nanoscale. , such as the quantum Hall effect and the operation of topological insulators (materials that conduct current perfectly at its edges and not at its volume). For many applications, it would be useful for us to be able to achieve the same for vibrations and sound waves and therefore break the symmetry of their propagation, so that it is no longer symmetrical in time inversion “.
Magnetic field for sound
Unlike electrons, mechanical vibrations have no charge and therefore do not respond to magnetic fields. However, they are sensitive to light radiation pressure. Therefore, Verhagen’s group used laser light to influence mechanical nanoresonators. In 2020, they used these same vibrating strings to show that the symmetry of the inversion of time could be broken for the sound that jumps from one resonator to another: the transfer of sound from one string to another is different than in the opposite direction. See also the news of February 3, 2020. “We have now shown that if we make a network of multiple vibrating nanocords, we can perform a series of unconventional vibrational patterns by illuminating the strings with laser light,” says Verhagen. “For example, we managed to get sound particles (phonons) to move in a single direction in the same way as electrons in the quantum Hall effect.”
Amplification
The researchers realized that they could also use radiation pressure to control sound amplification and attenuation. “This works in a similar way to a child on a swing that stretches or stretches its legs back at the right time,” explains Verhagen. “This amplification or attenuation is not possible for electrons in a magnetic field.”
The researchers realized that they could use radiation pressure to control sound amplification and attenuation. This works in a similar way to this child on a swing that stretches or pulls its legs back at the right time. Credit: Petra Klerkx
The researchers were the first to conduct experiments in which conduction light amplifies sound waves and at the same time ensures that they experience an effect similar to that of a magnetic field. “We’ve found that the combination of amplifying and breaking the symmetry of time inversion leads to a number of new and unexpected physical effects,” says Verhagen. “First, the laser light determines the direction in which the sound is amplified. In the other direction, the sound is blocked. This is caused by a geometric phase: a magnitude that indicates the extent to which the sound wave It moves through the network of nanochords, which in this case is caused by radiation pressure.Our experiment allowed us to fully control and alter this geometric phase.In addition, we used radiation pressure. of light to amplify sound This sound can even begin to oscillate spontaneously, like light in a laser We have discovered that the geometric phase we apply determines whether this happens or not, and with what force amplification “.
New materials
The researchers found that new geometric phases could be performed on systems where this was not considered possible. In all of these, the phases influence the amplification, direction, and pitch of the sound waves. “Geometric phases are important in many branches of physics, as they describe the behavior of different systems and materials. When combined with magnetic fields, they can give rise to a topological isolator for electrons, but the properties of a variant.” “We know that this is not going to be the case. We know that this will not be like anything we know,” said Verhagen. “We could further investigate the effects of linking more nano-chains in acoustic ‘metamaterials’ that we control with light. But the effects we have observed should be applied to a series of uncharged waves, such as light, microwaves, cold atoms, etc. We hope that with the new mechanisms we have discovered, it will be possible to produce new (meta) materials with properties that we do not yet know of existing materials. “
These materials and systems have unusual properties that can have useful applications. Verhagen: “It’s still too early to give a complete picture of the possibilities. However, we can already recognize some potential directions. For example, a one-way wave amplifier could have useful applications in quantum communication. We could also make sensors much more sensitive. breaking the symmetry of time inversion “.
Vibrations on a chip feel a magnetic field. More information: Ewold Verhagen, Non-Hermitian Chiral Phonics Through Optomechanically Induced Compression, Nature (2022). DOI: 10.1038 / s41586-022-04609-0. www.nature.com/articles/s41586-022-04609-0
Citation: Discovery of new mechanisms to control sound flow (2022, June 1) retrieved June 1, 2022 from
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