Subscribe to our free daily newsletters
. 24/7 Space News .

Subscribe to our free daily newsletters

Quantum Interference Demonstrated For First Time In Liquids

In the upper image the loop of a superfluid SQUID has no rotational flux from the Earth passing through it, so the wave functions of the two Josephson junctions are in phase and interfere constructively. Whereas in the lower image the superfluid SQUID loop has maximum rotational flux from the Earth passing through it, so the wave functions of the two Josephson junctions are out of phase and interfere destructively.
by Robert Sanders
Berkeley - August 8, 2001
In the quantum world, waves can act like particles and particles like waves, interfering like overlapping ripples in a pond.

Now, physicists at the University of California, Berkeley, have shown that this same quantum interference occurs between two samples of superfluid helium-3, a liquid so cold -- a thousandth of a degree above absolute zero -- that it flows without resistance. 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."

"Our experiment was a proof of principle, but if we can reduce the noise enough and build a much larger version of the device, it is conceivable that we could make a sensor to monitor small changes in the Earth's rotation," said J. C. Sťamus Davis, UC Berkeley professor of physics and researcher in the Materials Sciences Division of Lawrence Berkeley National Laboratory. "It's beautiful physics."

Davis, Packard, recent PhD Raymond W. Simmonds, former postdoctoral fellow Alexei Marchenkov and graduate student Emily Hoskinson report their findings in the July 5 issue of Nature.

This quantum interference is identical to the interference between light waves, electrons, atomic beams and electrical currents in solid superconductors. It had never before 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 today.

Just as superconducting dc-SQUIDs can measure minuscule magnetic fields, such as magnetic emanations from the brain, 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 predictions from Einstein's general theory of relativity, such as how spinning objects move in a gravitational field.

Four years ago, Davis, Packard and their colleagues demonstrated one of the basic components of the superfluid SQUID -- a superfluid Josephson junction, analogous to the Josephson junctions in superconductors.

In superconductors, a thin insulator between two superconductors at different voltages generates a microwave oscillation in the junction. This is in contrast to a classical circuit, where current flows in only one direction -- from high to low voltage.

Two Josephson junctions looped together create oscillating electrical currents that interfere, like beats in interfering sound waves. The beat pattern changes as the magnetic field enclosed in the loop changes, allowing an extremely precise field measurement.

In superfluids, pushing ultracold helium-3 through a perforated Silican wall generates a vibration as the fluid sloshes back and forth through the wall's 4,225 holes. Classically, liquids always flow from high to low pressure.

The researchers confirmed these quantum oscillations in 1997 by placing a sensitive superconducting SQUID microphone in the fluid and detecting a high-pitched whistle.

For the current experiment, they took two superfluid Josephson junctions and placed them on either side of a doughnut-shaped tube in hopes of detecting a beat pattern produced by interfering superfluid wavefunctions at the two junctions.

Just as a superconducting SQUID is sensitive to magnetic fields, a superfluid SQUID is sensitive to rotation. 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.

In a vivid demonstration of the phase shifting, as the researchers tilted the loop relative to the rotation axis of the Earth, the loudness changed as predicted.

The researchers had to conduct the experiments over the Christmas and New Year's holidays so they could shut down the heating and cooling systems in UC Berkeley's Birge Hall to reduce extraneous vibrations. The vibrations they detected are 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, who recently received his physics PhD from UC Berkeley, 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."

The work was supported by the National Aeronautics and Space Administration, the Office of Naval Research and the National Science Foundation.

Related Links
Physics at Berkeley
Search SpaceDaily
Subscribe To SpaceDaily Express

High-Tech Helium Tricks May Benefit Earth And Space
Pasadena - May 18, 2001
Imagine turning on your faucet and watching water flow out and then flow right back up into the faucet. NASA scientists have observed a similar phenomenon by using superfluid helium-4 in laboratory research that could improve earthquake prediction and spacecraft navigation.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.