From quantum to relativity: this quantum entanglement experiment detects Earth's rotation

Quantum entangled photons have recently revealed Earth's rotation through a groundbreaking experiment conducted by a team led by Philip Walther from the University of Vienna.

This advancement opens new horizons at the intersection of quantum mechanics and general relativity, surpassing the sensitivity limits of entanglement-based sensors.


Optical Sagnac interferometers, known for their unparalleled precision, have played a crucial role in measuring rotational velocities for decades. However, interferometers using quantum entanglement promise even greater sensitivity, although their potential has been limited by the delicate nature of entanglement.

The Viennese experiment overcame this barrier by constructing a giant optical fiber Sagnac interferometer capable of maintaining a low and stable noise level for several hours. This allowed the detection of high-quality entangled photon pairs, surpassing the precision of previous interferometers by a factor of a thousand.

In a Sagnac interferometer, two particles traveling in opposite directions on a closed path reach the starting point at different times. With entangled particles, the effect is amplified, their behavior resembling that of a single particle testing both directions simultaneously and accumulating twice the time delay.

To isolate Earth's rotational signal, the researchers divided the optical fiber into two equal parts connected by an optical switch. By toggling this switch on and off, they were able to neutralize the rotation signal.

This experiment, conducted as part of the TURIS research network, demonstrated the interaction between rotating systems and quantum entanglement with precision a thousand times greater than previous experiments. This work paves the way for future improvements and new explorations of quantum entanglement in the curvatures of space-time.