Novel device generates phonons at extremely cold temperatures

Modern communication usually rides on beams of light or pulses of electricity. But in environments where light and electronic signals break down, like the deep ocean or on board a spaceship, sound takes the lead.

Now, researchers at McGill University have found a way to create the smallest building blocks of sound: phonons, particles that act as fundamental pockets of vibration. Working at ultra-cold temperatures, they built a device that can generate phonons with extraordinary precision.

This innovation is to create a sounding “laser” rather than a light one. Phonon lasers could potentially transmit signals across environments where optical methods break down, paving the way for non-invasive imaging inside a living body.

The device works like a microscopic racetrack carved into a crystal just a few atoms thick. When an electrical current is sent through this narrow channel, electrons are trapped and forced to sprint forward. If pushed hard enough, they shed their energy in the form of tiny, sound‑like vibrations called phonons, released in neat, tunable bursts.

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The researchers cool the system to temperatures of 10 millikelvin to 3.9 kelvin to make this delicate process possible. At these temperatures, electrons behave predictably quantum-mechanically, and they behave more like waves than particles. Such extreme cold turns the crystal channel into a stage for electrons to perform a quantum “dance”, producing phonons that could eventually be used to power sound lasers for communication and disease diagnosis.

Michael Hilke, Associate Professor of Physics and study co-author, said, “At absolute zero temperatures – that is, the world of quantum physics – no sound is created unless electrons travel collectively at the speed of sound or above. Earlier work had observed similar effects as electron speeds approached the speed of light. Our study goes further by pushing the system well beyond that point and showing that existing theories need to be reassessed by considering that electrons can be very hot even if the host crystal is close to absolute zero temperature.”

In future work, the researchers seek to replace the crystalline channel with other materials, such as graphene. Because of its single-atom thickness and the ultra-high speeds at which electrons travel in graphene, phonon generation could be faster and more efficient.

These developments could transform the prototype into a multifunctional platform suitable for high-throughput communications, ultrasensitive diagnostics, and advanced medical technologies. By changing the “stage” on which electrons do their quantum shenanigans, the team may be opening a new chapter in which sound-photon lasers become viable technology for information transport and biological investigations.

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Hilke said, “Phonons are hard to generate and harness in a controlled way, so we are exploring new regimes. At a broad level, this is about how electrical current and energy move and are converted inside advanced electronic materials.”

Journal Reference:

1. Michael Hilke et al. Resonant magnetophonon emission by supersonic electrons in ultrahigh-mobility two-dimensional systems. Physical Review Letters. DOI: 10.1103/m1nb-j1h6