Researchers at McGill University have developed a tiny quantum device that generates precisely controlled sound-like particles called phonons at temperatures just above absolute zero — a breakthrough that could lead to phonon lasers, faster underwater communications, and new medical diagnostic tools.
Published in Physical Review Letters, the study demonstrates a new way to produce and control quantum sound by pushing electrons through an ultra-thin two-dimensional crystal at extreme speeds.
"Modern communication is largely based on light, including electromagnetic waves and electrical currents. In a medium such as oceans, sound can travel, whereas light and electrical currents cannot," said Michael Hilke, Associate Professor of Physics at McGill and co-author of the study. "In the human body, sound waves can also be a useful tool."
How it works
The team created a device using a two-dimensional crystal that confines electrons to a channel only a few atoms wide. When an electrical current pushes electrons through this ultra-thin pathway at high speeds, the electrons release their excess energy as controlled bursts of phonons.
The experiments were conducted at temperatures from 10 milli-Kelvin to 3.9 Kelvin — near absolute zero. At these extremes, electrons behave in orderly quantum fashion, making the phonon emission observable and controllable.
"At absolute zero temperatures — the world of quantum physics — no sound is created unless electrons travel collectively at the speed of sound or above," Hilke explained. Existing theories predicted certain limits, but this work pushes well beyond them, showing that electrons can be very hot even when the host crystal is near absolute zero.
What it enables
Phonon lasers — the sound-based equivalent of optical lasers — have been a long-standing goal in physics. Unlike light, sound penetrates water and biological tissue efficiently, opening applications where optical lasers struggle:
- Underwater communications: Sound travels far better than light or radio waves in water, enabling new underwater networks. - Medical diagnostics: Phonon-based imaging could see deeper into tissue than ultrasound while offering higher resolution. - Quantum sensing: Precisely controlled phonons could measure gravitational fields and material properties with extraordinary sensitivity.
The next phase will investigate using graphene, which could allow the device to operate at higher speeds and bring phonon laser technology closer to practical reality.
