Quantum Loops

Physicists deal with unimaginable things… things such as liquids that can flow without resistance. Superfluid helium-3 is one such liquid, but it exists only at an equally unimaginable temperature, a thousandths of a degree above absolute zero. Yet, because it flows without resistance, it flows endlessly.

Now, physicists at the University of California, Berkeley, funded in part by the Office of Naval Research, have built a device using superfluid helium-3 that behaves just like a superconducting quantum interference device, or SQUID. SQUIDs are the most sensitive detectors of magnetic fields known today. SQUIDs use the flow of supercurrents through loops as ultra-sensitive sensors of the magnetic fields threading the loop. The new device uses insteadthe flow of the superfluid, and can instead measure (again ultra-sensitively) the rotation of the loop. Rotation sensors are otherwise known as gyroscopes, and are of great importance to the Navy for navigation.

Just as the usual superconducting SQUIDs can measure such miniscule things as magnetic emanations from the human brain, superfluid SQUIDs detect miniscule changes in rotation. In preliminary experiments the group at Berkeley was able to detect the rotation of the Earth about its axis.

The potential is there for such a superfluid SQUID-like device to measure rotation thousands of times more sensitively than we can measure them today with state-of-the-art ring-laser gyroscopes. In the world of navigation and guidance this is momentous news.

"Inertial guidance systems, based on gyroscopes, are used in everything from spacecraft navigation to distant planets, to precise targeting of missiles, to the maneuvering of submarines, and this is exactly why the Navy is interested in them," says Dr. Peter Reynolds, ONR joint program manager on the project with Dr. Deborah van Vechten. "What this tells us is that a gyroscope could eventually be built that would be orders of magnitudes better than anything we have today."