Quantum entanglement measures Earth’s rotation like never before

The experiment is depicted by plotting an interferogram of Sagnac fibers within a magnified frame starting at a local position (Vienna, Austria) of the rotating Earth. Two indistinguishable photons fall on a beamsplitter cube, are entangled, and are then coupled in a fiber interferometer. Credit: Marco De Vita

A quantum physics experiment at the University of Vienna has achieved groundbreaking accuracy in measuring Earth’s rotation using entangled photons.

The study uses an improved Sagnac optical interferometer that leverages quantum entanglement to detect spin effects with unprecedented precision, offering potential breakthroughs in both quantum mechanics and general relativity.

Pioneering quantum experiment

A team of researchers conducted a pioneering experiment in which they measured the effect of the Earth’s rotation on quantum entangled photons. The work, led by Philipp Walter of the University of Vienna, has just been published in the journal Advancement of science. It represents a major breakthrough that pushes the limits of spin sensitivity in entanglement-based sensors, paving the way for further exploration at the intersection between quantum mechanics and general relativity.

Advances in Sagnac interferometers

Sagnac optical interferometers are among the most sensitive to rotation. It has been central to our understanding of fundamental physics since the early years of the last century, contributing to the establishment of Einstein’s theory of special relativity. Today, its unparalleled accuracy makes it the ideal tool for measuring rotational speeds, which are limited only by the limits of classical physics.

The Sagnac interferometer is made of 2 km long optical fibers wrapped around a 1.4 m long square-sided aluminum frame. Credit: Rafael Silvestri

Quantum entanglement enhances sensitivity

Interferometers that use quantum entanglement have the potential to break those limits. If two or more particles are entangled, only the aggregate state is known, while the state of the individual particle remains undetermined until measurement. This can be used to obtain more information for each measurement than would be possible without it. However, the promised quantum leap in sensitivity has been hampered by the extremely precise nature of entanglement.

Here the Vienna experience made the difference. They built a giant Sagnac fiber-optic interferometer and kept the noise low and stable for several hours. This enabled the detection of sufficient high-quality entanglement Photon Such pairs outperform the spin resolution of previous Sagnac quantum optical interferometers by a thousand times.

Innovative techniques in quantum measurement

In a Sagnac interferometer, two particles move in opposite directions of a closed, rotating path and arrive at the starting point at different times. With two entangled particles, it gets scary: they behave like a single particle experiencing both directions simultaneously while accumulating twice the delay compared to a scenario where there is no entanglement. This unique property is known as ultra-precision. In the actual experiment, two entangled photons were propagating within a 2-kilometre-long optical fiber wrapped in a huge coil, creating an interferometer with an effective area of ​​more than 700 square metres.

Overcoming challenges in quantum experiments

One of the big hurdles the researchers faced was isolating and extracting the Earth’s fixed rotation signal. “The essence of the matter is to create a reference point for our measurements, where the light remains unaffected by the influence of the Earth’s rotation,” explains lead author Raffaele Silvestri. “Since we cannot stop the Earth’s rotation, we devised an alternative solution: splitting the optical fiber into two coils of equal length and connecting them via an optical switch.” .

By toggling the switch on and off, the researchers were able to effectively cancel the rotation signal at will, which also allowed them to extend the stability of their larger device. “We basically tricked the light into thinking it existed in a non-rotating universe,” Silvestri says.

Confirm quantum mechanics and relativistic interactions

The experiment, conducted as part of the TURIS research network hosted by the University of Vienna and the Austrian Academy of Sciences, succeeded in observing the effect of Earth’s rotation on the maximally entangled photon state. This confirms the interaction between rotating reference systems and quantum entanglement, as described in Einstein’s special theory of relativity and quantum mechanics, with accuracy improved a thousand-fold compared to previous experiments.

“This represents a significant event in a century since the first observation of the Earth’s rotation with light, where the entanglement of individual quanta of light finally entered the same sensing systems,” says Haokun Yu, who worked on the experiment as a researcher at Marie Curie University. Postdoctoral fellow.

“I believe our results and methodology will pave the way for further improvements in the spin sensitivity of entanglement-based sensors. This may open the way for future experiments testing the behavior of quantum entanglement across space-time curves,” adds Philipp Walther.

Reference: “Experimental observation of the Earth’s rotation with quantum entanglement” by Raffaele Silvestri, Haokun Yu, Theodor Stromberg, Christopher Helwig, Robert W. Peterson, and Philip Walther, June 14, 2024, Advancement of science.
doi: 10.1126/sciadv.ado0215