In the realm of physics, a "perfect" fluid is one that flows with the smallest amount viscosity possible under quantum mechanics. It's predicted that you'd find them occurring naturally in the core of neutron stars.
A group of MIT scientists recently created one artificially, and they blasted it with sound waves to see how it would respond.
Very trippily! Here's an audio file, which sounds like someone twiddling the dial on Moog ….
This recording is a product of a glissando of sound waves that the team sent through a carefully controlled gas of elementary particles known as fermions. The pitches that can be heard are the particular frequencies at which the gas resonates like a plucked string.
The researchers analyzed thousands of sound waves traveling through this gas, to measure its "sound diffusion," or how quickly sound dissipates in the gas, which is related directly to a material's viscosity, or internal friction.
Surprisingly, they found that the fluid's sound diffusion was so low as to be described by a "quantum" amount of friction, given by a constant of nature known as Planck's constant, and the mass of the individual fermions in the fluid. [snip]
"It's quite difficult to listen to a neutron star," says Martin Zwierlein, the Thomas A. Frank Professor of Physics at MIT. "But now you could mimic it in a lab using atoms, shake that atomic soup and listen to it, and know how a neutron star would sound."
(That image above, by Christine Daniloff, comes via the MIT press release)