Physicists propose new quantum device to measure how Earth twists space-time

Scientists have proposed a new tabletop device designed to detect the subtle way Earth’s daily spin on its axis twists the surrounding space-time — an effect predicted by Einstein’s general relativity.

If constructed, the sensor could measure the quantum effect known as frame dragging with the same precision as the most advanced satellite experiments, yet in a matter of minutes rather than years, the researchers proposed in a new study.

The research, published on September 17 in the journal Physical Review Letters, sought to address a longstanding discrepancy in physics.

Consider a ring of clocks bolted to a spinning merry-go-round. Each clock is synchronized with its neighbor around the ring, but when the last clock is compared with the first, they do not match.

Gravity’s a drag

Frame dragging is a phenomenon that occurs when a massive, spinning object drags the fabric of space-time along with it, analogous to a spoon twirling in honey. The effect is clearly visible around supermassive objects, such as the Milky Way’s central black hole. However, around Earth, the effect is extremely faint.

So far, scientists have measured Earth’s frame dragging only from orbit. They tracked how the twisting of space-time slowly shifts spinning gyroscopes or the paths of satellites. In 2011, NASA’s Gravity Probe B satellite, which carried four gyroscopes, confirmed Einstein’s prediction with a margin of error of about 18%. Satellites tracked with lasers have since achieved even better results. In July, researchers reported in the journal Nature that the LARES-2 satellite had reduced that margin of error to just 0.2%.

However, that achievement required approximately three years of laser tracking. Researchers also had to account for the fact that Earth bulges at the equator and its mass is distributed unevenly, which introduces gravitational irregularities that tug on satellites far more strongly than frame dragging. To subtract those unwanted influences, the team relied on detailed maps of Earth’s gravity obtained from other satellites.

Measuring frame dragging with greater precision serves as a way to stress-test general relativity. Several alternative theories of gravity predict a slightly different magnitude of this twisting, and a laboratory-based measurement would also be free of the modeling assumptions that satellite experiments depend on, Ellers explained.

A quantum loop

The new device consists of a loop of superfluid helium-4 — helium chilled until it flows without friction and behaves like a single, giant quantum object. The loop is interrupted by a thin barrier riddled with tiny holes, referred to as a Josephson junction. Superfluid helium can pass through the holes, whereas ordinary liquid helium cannot.

“That is where the quantum behavior originates,” said K. Birgitta Whaley, a quantum physicist at UC Berkeley and co-author of the study.

As Earth spins and drags space-time, it perturbs the quantum state of helium flowing through the junction. This perturbation shifts the frequency of the helium’s oscillation within the loop, a change that the researchers could detect.

(Image credit: NASA)

Ellers, K.-I., Christodoulou, M., Schwab, K. C., & Whaley, K. B. (2026). Quantum sensing of gravitational frame dragging with a superfluid ⁴He gyrometer. Physical Review Letters, 137(12), 121404.

Scientists have proposed a new tabletop device designed to detect the subtle way Earth’s daily spin on its axis twists the surrounding space-time — an effect predicted by Einstein’s general relativity. If constructed, the sensor could measure the quantum effect known as frame dragging with the same precision as the most advanced satellite experiments, yet in a matter of minutes rather than years, the researchers proposed in a new study. The research, published on September 17 in the journal Physical Review Letters, sought to address a longstanding discrepancy in physics. Consider a ring of clocks bolted to a spinning merry-go-round. Each clock is synchronized with its neighbor around the ring, but when the last clock is compared with the first, they do not match. This represents a phenomenon known as frame dragging. As Earth spins and drags space-time, it perturbs the quantum state of helium flowing through the junction. The perturbation shifts the frequency of the helium’s oscillation within the loop, a change that the researchers could detect. Einstein’s theory of general relativity predicts that a massive, spinning object drags the fabric of space-time along with it, analogous to a spoon twirling in honey. The effect is clearly visible around supermassive objects, such as the Milky Way’s central black hole. However, around Earth, the effect is extremely faint. So far, scientists have measured Earth’s frame dragging only from orbit. They tracked how the twisting of space-time slowly shifts spinning gyroscopes or the paths of satellites. In 2011, NASA’s Gravity Probe B satellite, which carried four gyroscopes, confirmed Einstein’s prediction with a margin of error of about 18%. Satellites tracked with lasers have since achieved even better results. In July, researchers reported in the journal Nature that the LARES-2 satellite had reduced that margin of error to just 0.2%. However, that achievement required approximately three years of laser tracking. Researchers also had to account for the fact that Earth bulges at the equator and its mass is distributed unevenly, which introduces gravitational irregularities that tug on satellites far more strongly than frame dragging. To subtract those unwanted influences, the team relied on detailed maps of Earth’s gravity obtained from other satellites. Measuring frame dragging with greater precision serves as a way to stress-test general relativity. Several alternative theories of gravity predict a slightly different magnitude of this twisting, and a laboratory-based measurement would also be free of the modeling assumptions that satellite experiments depend on, Ellers explained. The new device consists of a loop of superfluid helium-4 — helium chilled until it flows without friction and behaves like a single, giant quantum object. The loop is interrupted by a thin barrier riddled with tiny holes, referred to as a Josephson junction. Superfluid helium can pass through the holes, whereas ordinary liquid helium cannot. “That is where the quantum behavior originates,” said K. Birgitta Whaley, a quantum physicist at UC Berkeley and co-author of the study. As Earth spins and drags space-time, it perturbs the quantum state of helium flowing through the junction. This perturbation shifts the frequency of the helium’s oscillation within the loop, a change that the researchers could detect. Superfluid devices, many of them built at UC Berkeley, have detected Earth’s rotation since the late 1990s. But the helium-4 versions built around a Josephson junction, like the new design, have operated within about a hundredth of a degree of 2.17 K (minus 455.76 Fahrenheit, or minus 270.98 Celsius), the temperature at which helium-4 becomes a superfluid. At that temperature, a lingering fraction of normal helium mixed with the superfluid adds noise. Instead, the team calculated how the device would behave at a few thousandths of a degree above absolute zero. Below 0.7 K, the noise changed character, and the team found it drops sharply as the helium gets colder. One key finding in the new paper is the result of the team’s thermal noise analysis, which showed how sensitive these devices could be at millikelvin temperatures, Ellers explained. The catch is the barrier. Earlier helium-4 devices used holes about 90 nanometers wide. Working at these frigid temperatures demands much smaller holes, about 1 nanometer across — roughly the size of a helium atom. Keith Schwab, a physicist at Caltech and co-author of the study, and his collaborators are developing such materials, but they have not yet been built into a working sensor. If they can be, the researchers calculate that the device could measure frame dragging to 0.2% precision in about 35 minutes. If its vibrating membrane were made from the lowest-loss crystals, such as quartz or sapphire, that could drop to about one second, they said. “This seems to be a very serendipitous discovery that at millikelvin, we can get this high sensitivity,” Whaley told Live Science. The signal corresponds to a time difference of about 10-35 seconds between helium flowing one way around the loop and the other — the same mismatch observed with the clocks on the metaphorical merry-go-round. The interesting thing about it is just how small it is. Whaley explained. “It is not so far off from the Planck time,” about 10-44 seconds, the shortest slice of time before the known laws of physics are expected to break down. This experiment is still a billion times too large to reach that limit, Whaley said. But future helium experiments could help explore whether time flows smoothly, like a ramp, or ticks forward in tiny, indivisible jumps, like the frames of a movie.

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