A group of physicists were able to make a measurement of the Earth’s rotation using photons – the particles of light – and experienced a strange quantum phenomenon called entanglement. This allows them to increase the accuracy of the measurement a thousandfold, and it can be used to investigate questions in fundamental physics.
You may wonder why this wasn’t implemented sooner. The answer is that quantum entanglement is a very delicate state. Two particles are entangled and suddenly belong to a single state. No matter how far apart they are, the interaction with one will affect the other – but the state can be disturbed and the particles move back completely separate from each other.
One way to measure rotations using light is with an instrument called the Sagnac interferometer. Light is sent through a loop in opposite directions, and the rotation of the system causes one side to return to the start at different times. If the light in question consists of a pair of entangled photons moving in opposite directions, something very strange happens. It’s like sending the same light in both directions at the same time and doubling the time delay between the two.
To take advantage of this property, called super-resolution, researchers at the University of Vienna sent entangled photons through a 2-kilometer-long fiber optic, organized in a loop. They managed to keep the system’s noise low and stable for hours, allowing entangled photons to survive the journey through.
Such a device is made to actively measure rotation, and there is a rotation source under our feet. The earth. This device finally brings quantum mechanics to a level of sensitivity previously only achieved with standard non-entangled light.
“That represents an important milestone since, a century after the first observation of Earth’s rotation with light, the entanglement of individual light quantas has finally entered the same sensitivity regimes,” co-author Haocun Yu, who worked on this experiment as Marie. -Curie Postdoctoral Fellow, said in a statement.
But actually measuring the Earth’s rotation was not the purpose of this device. The Sagnac interferometer was designed as a way to accurately measure the rotation of systems, independent of the Earth’s rotation. For this reason, the team had to find a way to isolate the rotation that comes from being on a rotating planet.
The Sagnac interferometer in the experiment. Two kilometers of optical fibers are coiled around a square aluminum frame 1.4 meters long.
Image credit: Raffaele Silvestri
‘The heart of the matter lies in establishing a reference point for our measurement, where light is not affected by the Earth’s rotation effect. Considering our inability to stop [Earth] We came up with a solution: split the optical fiber into two coils of equal length and connect them together via an optical switch,” explains lead author Raffaele Silvestri.
This solution, which essentially involved having a switch on the device, allowed them to neutralize the Earth’s rotation signal. “We basically tricked light into thinking it was in a non-rotating universe,” Silvestri continued.
The breakthrough is the first step towards a new way to measure rotation, and not only that; the researchers have great expectations of possible future applications.
“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,” added senior author Philip Walther adds. .
The study was published in the journal Science Advances.