What's the sound of one atom moving? That might sound a bit like a silly philosophical question, but actually it's a scientific puzzle that's now been solved.

If you're wondering why the headline isn't a more click bait-like "Listen to the Sound a Single Atom Makes," it's because you won't be able to hear it. In fact, the scientists claim that the noise is the softest sound that is physically possible.

The researchers, from Columbia University and Sweden's Chalmers University of Technology, captured the sound that a single atom makes when it moves by detecting the vibrations emanating from it. Just like you learned at school, vibrations create sound—it's just, in this case, the sound is very, very quiet indeed.

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So how did they do it? Well, they excited an atom, then detect its acoustic emissions using a specially made chip that converts miniscule acoustic waves into microwaves. Crucially, those microwaves are of large enough amplitude to actually be recorded—using low-temperature microwaving amplifiers—unlike their acoustic counterparts. Göran Johansson explained to Motherboard:

"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. It's the weakest possible sound possible at the frequency [that it vibrates]."

The results are published in Science. But why bother recording a sound so quiet? Well, because they can, for a start. But it's also a gateway to understanding the world of quantum sound, where quantized packets of sound—phonons—could be used in place of quantized packets of light, known as photons. Because sound moves more slowly than light, we might be able to more carefully probe and influence the quantum world if we can used sound. Just don't expect to hear about it when it happens. [Science via Motherboard]

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