In quantum physics waves and particles can act similarly, interfering like ripples in a pond and physicists at the University of California have shown that this interference occurs between two samples of superfluid helium-3. Helium-3 is so cold – a thousandth of a degree above absolute zero – that it is said to flow without resistance.
The discovery is said to mark the first demonstration of quantum interference in a liquid and one potential application of this quantum interference is in an ultrasensitive superfluid gyroscope.
‘The successful demonstration of this effect may enable scientists to measure extremely slight increases or decreases in the rotation of objects, including Earth,’ said Richard E. Packard, UC Berkeley professor of physics. ‘This device could even be used to establish an absolute state of rest.’
This quantum interference is reported to be identical to the interference between light waves, electrons, atomic beams and electrical currents in solid superconductors but had never been observed in a liquid.
The UC Berkeley physicists demonstrated quantum interference by building the first superfluid equivalent of a superconducting quantum interference device, called a dc-SQUID, the most sensitive detector of magnetic fields currently available.
A superfluid SQUID can detect changes in rotation, analogous to a gyroscope.
In addition to monitoring the Earth’s rotation, a superfluid gyroscope also could be used to test how spinning objects move in a gravitational field.
For the current experiment, they took two superfluid Josephson junctions and placed them on either side of a doughnut-shaped tube with the aim of detecting a beat pattern produced by interfering superfluid wavefunctions at the two junctions.
In their experiment, the rotation of the Earth shifted the relative phase of the fluid oscillating through the two junctions. When these oscillations are combined they produce an interference pattern.
The researchers connected a superconducting SQUID microphone to the doughnut-shaped tube to detect the quantum oscillations through the junctions, and heard a clear 273-Hertz tone.
To demonstrate the phase shifting the researchers tilted the loop relative to the rotation axis of the Earth, and the loudness changed as predicted.
The vibrations they detected were said to be 100,000 times smaller than a single atom. Davis, who in 1984 first began working with Packard on this project as a potential PhD thesis, was ecstatic that it finally worked.
‘It’s still strange to see quantum interference in a liquid, and to see the effect of the Earth’s rotation appear quantum mechanically in a tiny container of liquid,’ Davis said.
Simmonds added, ‘It’s truly amazing how the tiny helium atoms forming the superfluid sense the Earth’s rotation and communicate this quantum information over distances as big as my thumb, from one Josephson junction to the other.’