Like Sassy Teenagers, Atoms Talk Back

Researchers have captured sound from an artificial atom

Atom Sound Capture

An artificial atom generates sound waves consisting of ripples on the surface of a solid.Philip Krantz, Krantz NanoArt

If you talk to an artificial atom, it turns out the atom will say something back to you. Unfortunately, you won’t be able to hear it.

Researchers at Chalmers University of Technology in Sweden have communicated with an artificial atom in a lab. When they fed their atom extremely high frequency sound energy, the atom regurgitated the energy back to them in the form of sound waves. The researchers were then able to record these auditory rumblings with high-tech audio equipment, as the sounds were too high to be heard by human ears.

This absorption/emission interaction is very similar to how atoms interact with light. When a photon of light gets close enough to an atom, sometimes the atom will gobble it up, absorbing the photon into its body. However, atoms aren’t very good at holding this energy for long, so they usually spit it back out in the form of a light particle.

This concept has been extensively studied in the field of quantum optics, but it's the first time scientists have demonstrated such an interaction between artificial atoms and sound. Their study, published in the journal Science, provides researchers with a better understanding of the laws of quantum physics, which they hope to harness one day for making extremely fast computers.

Of course, these are artificial atoms doing the talking, not the natural ones -- but they get pretty close. Artificial atoms are like tiny electrical circuits that exhibit quantum mechanical properties. Technically, they are a collection of atoms, acting together as one big atom. Researchers like using artificial atoms for research, as they can easily change the atoms’ properties to suit their needs.

Artificial Atom

The artificial atom on the right can emit and absorb sound that moves across the surface of a microchip. The grey-blue structure on the left is the combined loudspeaker/microphone used to communicate acoustically with the atom.Martin Gustafsson and Maria Ekström

For this experiment, the Chalmers researchers placed an artificial atom on a specialized microchip. "What's unique about this microchip is it's a crystal that's able to convert electrical energy to sound energy," Martin Gustafsson, one of the researchers, tells Popular Science. And vice versa. So when electrical signals were applied to the device, they were converted to sound waves, traveling like ripples on the surface of the chip.

Then, when the waves reached the atom, the atom absorbed the energy and spit it back out, sending sound waves back across the microchip. The frequency of these sound waves was approximately 4.8 gigahertz; in musical terms, that translates to a D28, or 20 octaves above the highest note on a grand piano. To reach that note, you’d have to extend the piano 10 feet to the right.

Although these sound waves are too high for us puny humans, they are actually 100,000 times slower than light waves. Because of this, Gustafsson says working with sound opens up new possibilities for controlling quantum processes. “That means you have some chance to change settings or retune an atom while the sound particle is spreading,” he says. “With light, it’s moving so fast, you don’t have that time, and it’s difficult to keep control.”

Additionally, the artificial atoms are about 20 times larger than the wavelength of the sound used, affording the researchers much more control over the atom’s properties during experiments.

For now, Gustafsson says there are no real-world applications for their work yet, and that their study is more of a “curiosity driven piece of research.” But ultimately, understanding how atoms interact with sound is just one step in the researchers’ larger goal: dominating quantum mechanics -- a branch of physics that involves studying physical phenomena at tiny scales. Some processes of quantum mechanics have already been tapped for making super fast computers, but the field as a whole is still very much a mystery to scientists.

“What we have here is one tool in a toolbox for trying to generally get quantum mechanics to be something that we can control ourselves,” says Gustafsson.