UC Berkeley physicist Richard Packard and grad student Emile Hoskinson managed to hear the quantum vibrations, known as quantum whistles, of a supercold condensed fluid as it’s pushed through an array of tiny holes 1,000 times smaller than the diameter of a human hair. The audio recording sounds just like a penny whistle. As the pressure drops, so does the pitch.
…A chorus of thousands of nano-whistles produced a wail loud enough to hear. This is the first demonstration of whistling in superfluid helium-4. According to Packard and Hoskinson, the purity of the tone may lead to the development of rotation sensors that are sufficiently sensitive to be used for Earth science, seismology and inertial navigation…
“For 40 years, people have been trying to see something like this, but it has always been with single apertures,” Hoskinson said. “Maybe it’s true that you don’t get coherent oscillations with a single aperture, but somehow, with an array of apertures, the noise is suppressed and you hear a coherent whistle.”