The sound of a moving atom is silent to the human ears, but for the first time scientists have captured the sound a single atom makes when it moves.

Scientists at Chalmers University of Technology in Göteborg, Sweden discovered that the atom makes the softest sounds physically possible, identifying that the sound hits a "D-note."

The atom's sound is so soft that scientists could not hear it. Instead, the team of scientists constructed a millimeter long artificial atom and placed it on superconducting material to measure its electrical energy. The scientists excited the atom along the material to detect sound waves using a microphone chip that had long metallic "fingers" that captured and converted the acoustic waves so that they could see the sound in microwaves.

"The sound amplitude, or strength, is very weak. Basically, when you excite the atom, it creates a sound, one phonon at a time, according to theory," says study co-author Göran Johansson. "It's the weakest possible sound possible at the frequency [that it vibrates]."

Published in the journal Science, the study confirmed that sounds are made anytime something moves or vibrates no matter how small the matter is.

"According to the theory, the sound from the atom is divided into quantum particles," says study co-author Martin Gustafsson, a post-doctoral researcher at Columbia University. "Such a particle is the weakest sound that can be detected."

The scientists found the atom makes a "D-note," about 20 octaves above the highest note on the piano and a pitch inaudible to the human ear.

Although the scientists identified a sound that no one can hear, the study could help understand quantum sound where phonons, or packets of sound, can replace particles of light, known as photons. Photons are commonly used in quantum experiments, but their speed makes it difficult for scientists to manipulate. Because sound moves slower than light, the research could lead to developments in quantum computing.

"We have opened a new door into the quantum world by talking and listening to atoms," says study co-author and physics professor at the university, Per Delsing. "Our long term goal is to harness quantum physics so that we can benefit from its laws, for example in extremely fast computers."

Since the scientists were successful in seeing the microwaved sounds, they plan to continue experiments to record the sound. Keep an ear out for further developments in the future. 

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