Tabletop Quantum Device Could Measure How Earth Twists Space-Time

"It is impossible to synchronize that collection of clocks when you're in a rotating frame," Kai-Isaak Ellers, a physics graduate student at UC Berkeley and first author of the study, told Live Science.

The new device is a loop of superfluid helium-4 — helium chilled until it flows without friction and behaves as one giant quantum object. A thin barrier riddled with tiny holes, called a Josephson junction, interrupts the loop. Superfluid helium slips through those holes; ordinary liquid helium cannot.

"That's where the quantum behavior comes from," said co-author K. Birgitta Whaley, a quantum physicist at UC Berkeley.

As Earth spins and drags space-time, it nudges the quantum state of the helium passing through the junction. That nudge shifts the frequency at which the helium sloshes back and forth in the loop, and that shift is what the researchers could detect.

What stands between proposal and measurement?

Superfluid devices, many built at UC Berkeley, have detected Earth's rotation since the late 1990s. But helium-4 versions built around a Josephson junction have only worked within about a hundredth of a degree of 2.17 K (minus 455.76 F, or minus 270.98 C), the temperature where helium-4 becomes superfluid. At that temperature, leftover "normal" helium mixed into the superfluid adds noise.

The team instead calculated how the device would behave a few thousandths of a degree above absolute zero. Below 0.7 K, the noise changes character and then drops sharply as the helium gets colder. That thermal noise analysis, showing how sensitive these devices could be at millikelvin temperatures, is the paper's key finding.

"This seems to be a very serendipitous discovery that at millikelvin, we can get this high sensitivity," Whaley told Live Science.

Now the catch. Earlier helium-4 devices used holes about 90 nanometers wide. Millikelvin operation demands holes roughly 1 nanometer across — about the size of a helium atom. Co-author Keith Schwab, a Caltech physicist, and his collaborators are developing such materials. They have not yet been built into a working sensor.

If they can be, the researchers calculate the device could hit 0.2% precision in about 35 minutes. With a vibrating membrane made from the lowest-loss crystals, such as quartz or sapphire, that could drop to about one second.

What does this change for physics?

Right now, nothing measurable. The paper is a theoretical proposal plus a noise analysis, not an experimental result. The signal itself corresponds to a time difference of about 10⁻³⁵ seconds between helium flowing one way around the loop and the other — the same mismatch as the merry-go-round clocks.

"The interesting thing about it is just how small it is," Whaley said. "It's not so far off from the Planck time" — about 10⁻⁴⁴ seconds, the shortest slice of time before known physics is expected to break down.

This experiment remains a billion times too large to reach that limit, Whaley noted. Still, future helium experiments could probe whether time flows smoothly, like a ramp, or ticks forward in indivisible jumps, like the frames of a movie.

Until someone builds a working 1-nanometer barrier, the promise stays on paper. The idea is elegant. The hardware isn't here yet.