Scientists can now sculpt the quantum states of tiny particles to their liking—an odd yet mind-blowing revolution leading to some fascinating inventions. And the latest in the revolution is an odd device whose quantum properties could tackle the trickiest challenges in communications technology.
The device, described in a recent Physical Review Letters paper, generates phonons—a quantum mechanical description of vibrations in a material, similar to how photons are quantized light waves. Typically, phonons exist in a chaotic, entangled mix that makes them difficult for scientists to predict and control. However, the team designed the device to operate at extremely cold temperatures to bring out quantum effects, giving researchers a new pathway to control these frisky particles.
“Phonons are hard to generate and harness in a controlled way, so we are exploring new regimes,” Michael Hilke, the study’s co-author and a physicist at McGill University in Canada, said in a statement. “At a broad level, this is about how electrical current and energy moves and is converted inside advanced electronic materials.”
The sound of quantum
Phonons belong to a category of quantum phenomena called quasiparticles. This concept refers to a group of particles that behave collectively, such that it makes sense to see them as one entity. According to an MIT explainer, a phonon is a “fancy word” for a particle of heat, in the sense that heat spreading through a material represents the motion or vibration of atoms and molecules. The lower frequencies correspond to sound, and these vibrations must be a multiple of basic amounts of energy—quanta—proportional to the frequency.
However, phonons of different wavelengths can mix and mingle to reach new wavelengths, unlike photons, which don’t interact at all, making phonons difficult to work with. Given their close connection to heat dissipation, however, physicists had been striving to find a viable way to bring them into quantum technologies.
“In some cases, you want strong conduction of phonons, and in some cases you want to reduce their propagation,” Gang Chen, an engineer at MIT who wasn’t involved in the new work, explained in the MIT explainer. “Sometimes they’re good guys, and sometimes they’re bad guys.”
Frozen to obey
To overcome these challenges, the researchers behind the new study took things to the extreme. They cooled the devices to temperatures between roughly -459 and -452 degrees Fahrenheit (-272 and -269 degrees Celsius)—so barely above absolute zero—to force the particles, electrons in this case, to behave more predictably.
The electrons were trapped inside a channel with an area just a few atoms thick, then placed inside a two-dimensional crystal layer. When an electrical current passes through the crystal, the electrons are essentially driven through the channel, releasing energy as sound-like vibration bursts—phonons. Most importantly, these vibrations emerged in predictable, tunable patterns that the researchers could manipulate.
“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,” Hilke said. “Our study [shows] 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.”
Where light falters
While impressive, the device has a major, somewhat obvious hurdle to pass. As of now, extremely cold temperatures are required for the device to function properly. Needless to say, these conditions aren’t easily replicable outside research labs. This is something that the team acknowledges, and in the statement, Hilke noted the researchers were exploring whether other materials could improve the device’s performance.
Still, the idea of controllable phonons is attractive when imagining the next generation of technology, particularly in communications. For instance, sound signals are more versatile than light-based sources like electromagnetic waves and electric currents in specific environments, such as deep underwater and even inside the human body, Hilke said.
So the device might have a long way to go, but if it can weather tests for validity and practicality, it’ll truly represent a breakthrough in communications technology. That might be a big “if,” but who knows? The quantum revolution has brought some really unlikely advances already.
