Our days here on earth are not always 24 hours long. Earthquakes and cloud systems can subtly disrupt the planet's rotation, adding or subtracting fractions of a second. Current methods aren't sensitive enough to detect these wobbles, even when they stem from major tremors. A new device developed by experimental physicists at the University of California at Berkeley, though, may be able to track the fleeting daily discrepancies. Richard Packard and Samus Davis made a sort of gyroscope from supercold helium-3: the friction-free superfluid produces a whistling sound that gets louder or quieter depending on the orientation of the earth's axis of rotation.
"This research was an exciting breakthrough for us," Packard says. "The successful demonstration of this effect may enable scientists to measure extremely slight increases or decreases in the rotation of objects, including earth." The team first discovered the quantum whistle in 1997, when they pushed superfluid helium-3 through a single perforated membrane. This time, they placed thin perforated membranes at opposite sides of a doughnut-shaped container and again tried to push the fluid through using electrostatic pressure. Again they found the fluid did not flow in the direction in which they pushed, but rather followed an oscillating pattern and produced a high-pitched whine.
The oscillation and sound result directly from the interference of two superfluid quantum systems that are "linked" in the doughnut-shaped container. "In essence, we demonstrated that two weak links behave as one weak link whose properties are influenced by earth's rotation," Packard explains. "The successful demonstration of this effect has been a goal of low-temperature physicists for more than 35 years." They hope the superfluid helium whistle will eventually find a use in extremely precise gyroscopes for future spacecraft.