Quantum entanglement defies weightlessness

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Experiments in weightlessness
Experiments in weightlessness
The ÖAW and TU Vienna were able to show during a parabolic flight: A change in gravity has no influence on quantum experiments.

A team from the Austrian Academy of Sciences and the Vienna University of Technology was able to prove this during a flight with the European Space Agency: Quantum entanglement also works when the strength of gravity changes. Their quantum system was built so robustly that even changing gravity and vibrations during the flight had no effect on quantum entanglement. The results are an important starting point for future experiments at the interface between quantum physics and general relativity.

During a parabolic flight, the occupants of an airplane experience alternating phases in which they are exposed to increased G-forces and weightlessness, or more precisely microgravity. Researchers from the Austrian Academy of Sciences (ÖAW) and TU Vienna have taken advantage of this to test the influence of these alternating forces on a quantum system of entangled photons. They carried out their experiment on board an aircraft from Novespace, which performed a parabolic flight from Bordeaux in France on behalf of the European Space Agency (ESA).

Extreme conditions

"Although quantum states are very sensitive, thanks to considerable progress in experimental physics, we can now carry out exciting experiments outside the laboratory that are even robust enough to withstand the extreme conditions of a parabolic flight," explains Julius Bittermann from the Institute of Quantum Optics and Quantum Information at the Austrian Academy of Sciences, who also conducts research at the Atomic Institute at TU Wien.

The research team’s experiment consists of a source of entangled photon pairs, which are measured to determine the strength of the entanglement. "Through entanglement, both individual photons become part of a larger quantum system that can only be completely described as a whole. If I measure the polarization of a photon, the chance of obtaining one of the two possible states "horizontal" or "vertical" is 50 to 50. But no matter which result I get, I always know the state of the other photon, which must always have the other polarization in our entangled systems," explains Bittermann.

Entanglement remains stable

With their experiment, the researchers wanted to test whether the acceleration forces that occur during a parabolic flight have an influence on the sensitive entanglement of two photons. "We still have no unification between quantum physics and the general theory of relativity, which is our best description of gravity. This is why experiments that investigate the influence of so-called non-inertial motion on quantum systems are so interesting," says Bittermann. The result of the experiment was negative in this case. Neither microgravity nor hypergravity or the changes between the phases during the flight had a statistically significant effect on the quality of the entanglement of the photons.

A positive result would probably have been worthy of a Nobel Prize, but this was not the researchers’ expectation. "We provide another reference point for the interaction between acceleration forces and quantum systems. Our experiment shows that neither forces between 0 g and 1.8 g nor the change between them have any influence on polarization-entangled photons," says Bittermann.

In addition, the researchers from the Austrian Academy of Sciences and Vienna University of Technology have provided further proof that even very sensitive quantum experiments can now be handled so well that they function reliably outside the strictly controlled conditions of a laboratory.

Original publication

J.A. Bittermann et al, Photonic entanglement during a zero-g flight, Quantum 8, 1256 (2024).