The experiment was depicted by drawing an interferometric scheme of Sagnac fibers in a magnifying inset, starting from a local position (Vienna, Austria) of the rotating Earth. Two indistinguishable photons impinge on a beam splitter cube, entanglement occurs between them and then they are coupled in the fiber interferometer. Credit: Marco Di Vita
A quantum physics experiment at the University of Vienna achieved groundbreaking precision in measuring the Earth’s rotation using entangled photons.
The study uses an improved Sagnac optical interferometer that uses quantum entanglement to detect rotational effects with unprecedented precision, offering potential breakthroughs in both quantum mechanics and general relativity.
Groundbreaking quantum experiment
A team of researchers conducted a groundbreaking experiment measuring the effect of the Earth’s rotation on quantum entangled photons. The work, led by Philip Walther of the University of Vienna, has just been published in the journal Scientific progress. It represents a major achievement that pushes the boundaries of rotational sensitivity in entanglement-based sensors, potentially paving the way for further research at the intersection between quantum mechanics and general relativity.
Advances in Sagnac interferometers
Optical Sagnac interferometers are the most sensitive devices to rotations. They have been crucial to our understanding of fundamental physics since the beginning of the last century and contributed to the development of Einstein’s special theory of relativity. Today, their unparalleled precision makes them the ultimate tool for measuring rotational speeds, limited only by the limits of classical physics.
Sagnac interferometer built with 2 kilometers of optical fibers wrapped around a 1.4 meter square aluminum frame. Credit: Raffaele Silvestri
Quantum entanglement improves sensitivity
Interferometers using quantum entanglement have the potential to break these boundaries. When two or more particles are entangled, only the overall state is known, while the state of the individual particle remains undetermined until measurement. This allows more information to be obtained per measurement than would be possible without this method. However, the promised quantum leap in sensitivity is hampered by the extremely delicate nature of entanglement.
This is where the Vienna experiment made the difference. They built a giant Sagnac interferometer with optical fibers and kept the noise low and steady for several hours. This made it possible to detect sufficient high-quality entangled substances photon pairs that outperform previous quantum optical Sagnac interferometers by a thousand times.
Innovative techniques in quantum measurements
In a Sagnac interferometer, two particles traveling in opposite directions of a rotating closed path reach the starting point at different times. With two entangled particles, things get spooky: they behave like a single particle testing both directions at the same time, while building up twice the time delay compared to the no-entanglement scenario. This unique feature is known as super resolution. In the actual experiment, two entangled photons propagated in a two-kilometer-long optical fiber wound on a huge coil, creating an interferometer with an effective surface area of more than 700 square meters.
Overcoming challenges in quantum experiments
A major hurdle the researchers faced was isolating and extracting Earth’s stable rotation signal. “The crux of the matter,” explains lead author Raffaele Silvestri, “lies in establishing a reference point for our measurement, where light remains unaffected by the Earth’s rotation effect. Given our inability to stop the Earth from spinning, we came up with a solution: split the optical fiber into two coils of equal length and connect them via an optical switch.”
By turning the switch on and off, the researchers could effectively cancel the rotation signal as desired, also allowing them to increase the stability of their large device. “We essentially tricked light into thinking it was in a non-rotating universe,” Silvestri says.
Confirmation of quantum mechanics and relativity interactions
The experiment, conducted as part of the TURIS research network organized by the University of Vienna and the Austrian Academy of Sciences, successfully observed the effect of the Earth’s rotation on a maximally entangled state of two photons. This confirms the interaction between rotating reference systems and quantum entanglement, as described in Einstein’s special theory of relativity and quantum mechanics, with a thousandfold improvement in precision compared to previous experiments.
“That is an important milestone, since, a century after the first observation of the Earth’s rotation with light, the entanglement of individual light quantas has finally reached the same sensitivity regimes,” says Haocun Yu, who worked on this experiment as a Marie-Curie. Postdoctoral researcher.
“I believe that our result and methodology will lay the foundation for further improvements in the rotational sensitivity of entanglement-based sensors. This could open the way for future experiments testing the behavior of quantum entanglement through the curves of spacetime,” adds Philip Walther.
Reference: “Experimental observation of Earth’s rotation with quantum entanglement” by Raffaele Silvestri, Haocun Yu, Teodor Strömberg, Christopher Hilweg, Robert W. Peterson and Philip Walther, June 14, 2024, Scientific progress.
DOI: 10.1126/sciadv.ado0215