Physicists at the University of Vienna have used a maximally entangled quantum state of light paths in a large interferometer to experimentally measure the speed of the Earth’s rotation.
Silvestri othersThey have demonstrated the largest and most precise quantum-optical Sagnac interferometer to date, sensitive enough to measure the Earth’s rotation rate. Image courtesy of Marco Di Vita.
For over a century, interferometers have been key instruments for experimentally testing fundamental physical questions.
They disproved the ether as a light-transmitting medium, helped establish the theory of special relativity, and made it possible to measure tiny ripples in space-time itself known as gravitational waves.
Recent technological advances allow interferometers to work with a variety of quantum systems, including electrons, neutrons, atoms, superfluids, and Bose-Einstein condensates.
“When two or more particles are entangled, only the overall state is known; the states of the individual particles remain uncertain until they are measured,” said co-first author Dr. Philip Walther and his colleagues.
“Using this allows us to get more information per measurement than we would without it.”
“But the extremely delicate nature of quantum entanglement has prevented the expected leap in sensitivity.”
For their study, the authors built a large fiber-optic Sagnac interferometer that was stable with low noise for several hours.
This allows the detection of entangled photon pairs with a sufficiently high quality to exceed the rotational precision of conventional quantum-optical Sagnac interferometers by a factor of 1000.
“In a Sagnac interferometer, two particles moving in opposite directions on a rotating closed path reach a starting point at different times,” the researchers explained.
“When you have two entangled particles, you get a spooky situation: they behave like a single particle testing both directions simultaneously, accumulating twice the time delay compared to a scenario where no entanglement exists.”
“This unique property is known as super-resolution.”
In the experiment, two entangled photons propagated through a 2 km long optical fiber wound around a giant coil, creating an interferometer with an effective area of more than 700 m2.
The biggest hurdle the team faced was isolating and extracting the Earth’s stable rotation signal.
“The crux of the problem lies in establishing a measurement reference point where light is not affected by the Earth’s rotation,” said Dr Raffaele Silvestri, lead author of the study.
“Since we can’t stop the Earth’s rotation, we devised a workaround: split the optical fiber into two equal-length coils and connect them through an optical switch.”
“By switching it on and off, we were able to effectively cancel the rotation signal, which also increased the stability of larger equipment.”
“We’re basically tricking light into thinking it’s in a non-rotating universe.”
The research team succeeded in observing the effect of the Earth’s rotation on a maximally entangled two-photon state.
This confirms the interplay between rotating reference systems and quantum entanglement, as described in Einstein’s special theory of relativity and quantum mechanics, and represents a thousand-fold improvement in precision compared to previous experiments.
“A century after the first observations of the Earth’s rotation using light, this is an important milestone in that the entanglement of individual quanta of light is finally in the same region of sensitivity,” said co-first author Dr Haokun Yu.
“We believe that our findings and methods lay the foundation for further improving the rotational sensitivity of entanglement-based sensors.”
“This could pave the way for future experiments to test the behaviour of quantum entanglement through curves in space-time,” Dr Walther said.
Team work Published in a journal Scientific advances.
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Raffaele Silvestri others2024. Experimental Observation of Earth’s Rotation through Quantum Entanglement. Science Advances 10(24); doi: 10.1126/sciadv.ado0215
Source: www.sci.news
