AI-rewritten: This is a summary of an article from Phys.org, rewritten by AI (Qwen, running locally) to make it easier to read. The facts come from the original article – read it for the full story.

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Einstein’s theory of general relativity describes gravity as the bending of spacetime, a model that combines space and time into a single continuum. The theory predicts that a rotating object like Earth slightly drags the surrounding spacetime, a phenomenon known as frame-dragging. Researchers at UC Berkeley, the Austrian Academy of Sciences, and Caltech recently proposed using a quantum sensor to measure this tiny effect in a laboratory. Their idea involves cooling helium-4 until it enters a superfluid state, a phase where the liquid flows without friction below 2.17 Kelvin (about -271°C).

The team, led by theorists Kai-Isaak Ellers, Birgitta Whaley, and Marios Christodoulou, connected with experimental physicist Keith Schwab at Caltech to ground their proposal in reality. They plan to fill a doughnut-shaped tube with superfluid helium and detect changes in its flow using a barrier with tiny holes called a Josephson junction. When the device rotates, a quantum mechanical phase difference appears across this junction, which can be measured by tracking the motion of a connected mechanical diaphragm.

Previous sensors have successfully measured Earth’s rotation, but detecting the much smaller frame-dragging effect has been difficult due to thermal noise. The researchers propose cooling the sensor far below the superfluid transition temperature, potentially to 10 millikelvin. This extreme cold could reduce heat disturbances enough to match or exceed current measurement sensitivity with less time. Unlike past experiments requiring space-based observation, this design aims to be performed in a laboratory on Earth.

Beyond measuring rotation, the study suggests the sensor could reveal tiny differences in how time passes along different paths around the loop. This offers another way to test Einstein’s theory and potentially probe physical processes occurring on time scales near the Planck time. The team is now developing Josephson junctions capable of operating at millikelvin temperatures to move toward building the actual device.