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06-16-2024

Quantum entangled photons used to measure the Earth's rotation

In a remarkable feat of scientific exploration, a team of researchers has successfully measured the effect of Earth’s rotation on quantum entangled photons.

This pioneering experiment, conducted by a group led by Philip Walther at the University of Vienna, pushes the boundaries of rotation sensitivity in entanglement-based sensors.

These brilliant scientists have brought the world a step closer to the fascinating intersection between quantum mechanics and general relativity.

Their research represents a significant milestone in our understanding of the intricate relationship between rotating reference systems and quantum entanglement.

Sagnac sensation from optical interferometers

By employing a giant optical fiber Sagnac interferometer and maintaining low and stable noise levels for several hours, the team achieved a thousand-fold improvement in rotation precision compared to previous quantum optical Sagnac interferometers.

Optical Sagnac interferometers have long been recognized as the most sensitive devices for measuring rotations.

These instruments have played a crucial role in shaping our understanding of fundamental physics since the early years of the last century, contributing to the establishment of Einstein’s special theory of relativity.

Illustration showing Earth's rotation measured by quantum entangled photons. Credit: Marco Di Vita
Illustration showing Earth’s rotation measured by quantum entangled photons. Credit: Marco Di Vita

Today, their unparalleled precision makes them the ultimate tool for measuring rotational speeds, limited only by the boundaries of classical physics.

However, interferometers employing quantum entanglement to measure Earth’s rotation have the potential to break those bounds.

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 unique property can be harnessed to obtain more information per measurement than would be possible without entanglement.

Overcoming the delicate nature of entanglement

Despite the immense potential of entanglement-based sensors, their practical implementation has been hindered by the extremely delicate nature of entanglement.

This is where the Vienna experiment made a significant breakthrough.

The researchers constructed a massive optical fiber Sagnac interferometer, with two entangled photons propagating inside a 2-kilometer-long optical fiber wound onto a huge coil.

This setup realized an interferometer with an effective area of more than 700 square meters.

By keeping the noise low and stable for several hours, the team was able to detect enough high-quality entangled photon pairs to outperform the rotation precision of previous quantum optical Sagnac interferometers by a thousand times.

Tricking light in a spinning universe

One of the major challenges faced by the researchers was isolating and extracting Earth’s steady rotation signal.

“The core of the matter lays in establishing a reference point for our measurement, where light remains unaffected by Earth’s rotational effect,” lead author Raffaele Silvestri explains.

“Given our inability to halt Earth’s from spinning, we devised a workaround: splitting the optical fiber into two equal-length coils and connecting them via an optical switch.”

By toggling the switch on and off, the researchers could effectively cancel the rotation signal at will, allowing them to extend the stability of their large apparatus.

“We have basically tricked the light into thinking it’s in a non-rotating universe,” Silvestri concluded.

Quantum photons and Earth’s rotation

In a Sagnac interferometer, two particles traveling in opposite directions of a rotating closed path reach the starting point at different times.

However, when two entangled particles are involved, something extraordinary happens: they behave like a single particle testing both directions simultaneously while accumulating twice the time delay compared to the scenario where no entanglement is present.

This unique property is known as super-resolution.

The experiment, conducted as part of the research network TURIS hosted by the University of Vienna and the Austrian Academy of Sciences, successfully observed the effect of Earth’s rotation on a maximally entangled two-photon state.

This confirmation of the interaction between rotating reference systems and quantum entanglement, as described in Einstein’s special theory of relativity and quantum mechanics, represents a thousand-fold precision improvement compared to previous experiments.

“That represents a significant milestone since, a century after the first observation of Earth’s rotation with light, the entanglement of individual quanta of light has finally entered the same sensitivity regimes,” says Haocun Yu, who worked on this experiment as a Marie-Curie Postdoctoral Fellow.

Exploring the curves of spacetime

The successful demonstration of this methodology opens up exciting possibilities for future research.

Philip Walther, the lead researcher, believes that their result and methodology will set the ground for further improvements in the rotation sensitivity of entanglement-based sensors.

“This could open the way for future experiments testing the behavior of quantum entanglement through the curves of spacetime,” he adds.

Earth’s rotation unites Einstein with the quantum realm

This fascinating experiment marks a significant milestone in our understanding of the intricate relationship between quantum entanglement and the effects of Earth’s rotation.

By successfully measuring the influence of our planet’s spin on entangled photons with unprecedented precision, this research confirms the predictions of Einstein’s special theory of relativity and quantum mechanics while opening the door to a new era of exploration at the fascinating intersection of these two fundamental fields.

As scientists continue to push the boundaries of entanglement-based sensors, we stand on the brink of unraveling the mysteries of spacetime and gaining a deeper understanding of the universe’s most fundamental workings.

The full study was published in the journal Science Advances.

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