Physicists can now hear normally inaudible quantum vibrations/whistles, thanks to the work of scientists (Dr. Richard Packard, and grad. student Emile Hoskinson) at U. C. Berkley. Helium-4 at near absolute zero temperatures (less than 2 Kelvin) behaves like a superfluid. At this temperature, the liquid flows without friction, due to quantum effects, just like electricity loses all resistance in a superconductor.

Researchers with a cyrostat insert (Courtesy: Spacedaily)The scientists pushed this liquid through an array of apertures 1,000 times smaller than the width of a human hair. As the velocity of the fluid reached a critical level, a strange phenomenon known as the microscopic quantum whirlpool dashed through the apertures, thus sapping some of the liquid's energy. This instantly slowed the flow. Thus the liquid would speed up and slow down in the narrow channels, creating vibrations that produced a whistling sound going from high to low. You can hear the whistling at this NASA link.
So what are the benefits of this work, other than the nice whistling sound?! It is possible that this research might lead to enhanced earthquake studies, and more accurate navigation system (such as GPS). Temperatures as low as 2K can be synthesized easily using off-the-shelf components, and small vibrations in the earth, or small changes in the orientation of a satellite, can be more accurately measured with this technology.