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The BIG Bell Test Results Published

100.000 volunteers collaborate in a quantum physics experiment that challenges Einstein.

A collective physics experiment was conducted simultaneously in 11 laboratories around the world. Participants contributed to the experiment by generating over 90 million bits and unpredictably choosing how to perform measurements in their laboratories. The study was published on Nature.

On November 30, 2016, more than 100,000 people around the world contributed to a series of cutting-edge quantum physics experiments, known as The BIG Bell Test. Using an online video game, participants generated sequences of zeroes and ones (bit), in the most random way, which determines what measurements to perform on quantum objects such as atoms, photons and superconducting devices. The results have been now analysed and published in the NatureJournal.

In a Bell Test (named after the physicist John Stewart Bell), pairs of entangled particles are generated and sent to different places where their properties, such as the polarization of photons, are measured. In the BIG Bell Test, the bits produced by the participants were communicated via internet to the experiments conducted in Rome, Brisbane (Australia), Shanghai (China), Vienna (Austria), Munich (Germany), Zurich (Switzerland), Nice (France), Barcelona (Spain), Buenos Aires (Argentina), Concepción (Chile) and Boulder (USA), where they were used to set the angles of polarizers and other laboratory elements with the aim of determining what measurements to perform on the entangled particles.

"In the laboratory we observe that the results of measurements on two physically separate particles are correlated, regardless of which properties we choose to measure,” points out Fabio Sciarrino, Group Leader at the Sapienza Quantum Information Lab. “This implies something very surprising:  the measurement of one particle instantly influences the other one (although it is very far away), or the observed properties never existed, but rather were created by the measurement itself. Both these possibilities contradict local realism, Einstein's worldview, according to which the nature of the universe is independent from our observations."

Under the guidance of the ICFO-The Institute of Photonic Sciences in Barcelona, the BIG Bell Test requested the participation of volunteers from around the world – referred to as Bellsters- to choose what measures to carry out in order to close the so-called "Loophole of freedom choice" (i.e. the possibility that the particles themselves influence the choice of measurement). The existence of this kind of influence would invalidate the Bell test. It would be as if students were allowed to write their own exam questions.

"This Loophole,” explains Sciarrino, “cannot be eliminated by using dice or random number generators, because there is always the possibility that these physical systems are, in some form, connected with the entangled particles. Human choices introduce the element of free will, through which people can choose independently what the particles could do. Thus, for the first time, human unpredictability played a key role in a range of quantum physics experiments, some of which have never been carried out before."

In particular, the group headed by Fabio Sciarrino from the Sapienza Physics Department, the only Italian partner directly involved in the BIG Bell Test project, experimentally observed, for the first time, a new type of non-locality within a quantum network. The team, composed by young researchers, implemented a network with three interconnected nodes and two independent sources of quantum states, each of which produced a pair of entangled photons in their polarization. The experiment exploited human randomness for the choice of the settings in the measurements performed on each of these nodes.

This collective experiment allowed a Bell test and other similar tests on realism and locality in quantum mechanics to be performed, free from some strong assumptions that were previously needed. "The results,” concludes Sciarrino, “are not in line with Einstein's worldview. They close the Loophole of Freedom of Choice for the first time and demonstrate several new methods in the study of entanglement and local realism. Furthermore, this global experiment represents a demonstration of the maturity of emerging quantum technologies with implications ranging from cryptography to quantum networks."