A team of researchers, led by Philip Walther at the University of Vienna, conducted an experiment to measure the effect of Earth’s rotation on quantum entangled photons. The results of the experiment were published in Science Advances, showcasing a breakthrough in rotation sensitivity in entanglement-based sensors. This achievement has the potential to pave the way for further exploration at the intersection of quantum mechanics and general relativity. Interferometers using quantum entanglement have the ability to surpass the limitations of classical physics, providing more information per measurement compared to traditional methods. The delicacy of entanglement has hindered progress in this area, but the Vienna experiment managed to overcome this challenge by building a large optical fiber Sagnac interferometer that maintained low and stable noise levels for extended periods, resulting in a thousand-fold improvement in rotation precision compared to previous experiments.
Optical Sagnac interferometers have been crucial in our understanding of fundamental physics since the early 20th century and have played a key role in establishing Einstein’s special theory of relativity. These devices are currently the most accurate tools for measuring rotational speeds, limited only by classical physics. However, interferometers utilizing quantum entanglement have the potential to exceed these boundaries and offer a quantum leap in sensitivity. In a Sagnac interferometer, two entangled particles traveling in opposite directions behave as a single particle testing both directions simultaneously, leading to super-resolution. The Vienna experiment involved two entangled photons propagating inside a 2-kilometer-long optical fiber, creating an interferometer with an effective area of over 700 square meters.
One of the challenges faced by the researchers was isolating Earth’s steady rotation signal from the experiment. To overcome this, they split the optical fiber into two equal-length coils and connected them using an optical switch. By toggling the switch on and off, they could cancel the rotation signal at will, tricking the light into behaving as though it was in a non-rotating universe. This approach allowed the researchers to extend the stability of their apparatus and successfully observe the effect of Earth’s rotation on a maximally entangled two-photon state. This breakthrough confirms the interaction between rotating reference systems and quantum entanglement, aligning with Einstein’s special theory of relativity and quantum mechanics.
The Vienna experiment was part of the TURIS research network hosted by the University of Vienna and the Austrian Academy of Sciences, showcasing a thousand-fold improvement in rotation precision compared to previous experiments. This milestone marks a significant achievement, as the entanglement of individual quanta of light has now entered the same sensitivity regimes as the observation of Earth’s rotation with light over a century ago. The researchers believe that their results and methodology will lay the groundwork for further advancements in rotation sensitivity using entanglement-based sensors, possibly leading to future experiments exploring quantum entanglement behavior through spacetime curves. Philip Walther, the lead researcher, anticipates that these findings will open up new avenues for research at the intersection of quantum mechanics and general relativity.
