Quantum sound device points toward phonon lasers

Researchers have built a quantum device that can produce controlled bursts of phonons, the particle-like vibrations often described as quantum sound. McGill University said the result could support future work on phonon lasers, sound-based communication, medical diagnostics and sensing systems.

The device was developed and tested by researchers at McGill University and the National Research Council of Canada, according to McGill. The material used in the device was synthesized at Princeton University.

The findings were published in Physical Review Letters in a paper titled “Resonant Magnetophonon Emission by Supersonic Electrons in Ultrahigh-Mobility Two-Dimensional Systems.” The listed authors include Z. T. Wang, Michael Hilke, N. Fong, D. G. Austing, S. A. Studenikin, K. W. West and L. N. Pfeiffer.

How the device works

McGill said the team used a two-dimensional crystal that restricts electrons to a path only a few atoms wide. When electrical current drives the electrons through that narrow channel at high speed, the electrons shed excess energy as phonons.

The researchers found that the phonons could be generated in controlled, predictable patterns, according to McGill. That control is central to proposed devices that would use sound at the quantum scale, including phonon lasers.

Michael Hilke, a McGill physics associate professor and study co-author, said modern communications rely heavily on light, electromagnetic waves and electrical currents. He said sound can travel through media such as oceans where light and electrical currents cannot, and that sound waves also have uses in the human body.

Cold temperatures reveal unusual behavior

The experiments were conducted at temperatures from about 10 milli-Kelvin to 3.9 Kelvin, according to McGill. At such low temperatures, electron behavior becomes more orderly, allowing researchers to observe quantum effects more clearly.

Hilke said that near absolute zero, sound is not produced unless electrons move collectively at the speed of sound or faster. He said earlier work had seen related effects as electron speeds neared that threshold, while the new study pushed the system beyond it.

According to Hilke, the results suggest current theories need revision because electrons can become very hot even when the surrounding crystal remains close to absolute zero. McGill described the behavior as exceeding what existing models had predicted for how energy moves through advanced materials.

Next steps

McGill said the next stage of the research will test other materials, including graphene, which may allow higher-speed operation. Hilke said future versions of the technology could contribute to faster communication systems, more sensitive detectors, improved tools for studying biological materials and medical technologies.

Hilke said phonons are difficult to generate and control, and that the group is examining new regimes for converting electrical current and energy inside advanced electronic materials. The research was funded by the Natural Sciences and Engineering Research Council of Canada and the Fonds de recherche du Québec — Nature et technologie.

This story draws on original reporting from ScienceDaily.