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The BIG Bell Test in Nature: cooperative science to test quantum physics

An international collaboration established by the Institute of Photonic Sciences in Barcelona, which brought together 12 laboratories on 5 continents, including the Nice Institute of Physics (INPHYNI at the Université Côte d’Azur), has led to an unprecedented, joint, scientific experiment related to quantum physics. The results were published in the journal Nature on 10 May 2018.

Publication : 30/07/2018
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Quantum randomness is inherently different than classical randomness. This is what the violation of Bell’s inequalities shows and which was a turning point in the understanding of quantum physics. There is a downside though: testing these inequalities still relies on experimental configurations established using data generated by quantum systems. Thus, quantum physics must be tested with quantum physics. To alleviate this problem, an international collaboration established by the Institute of Photonic Sciences in Barcelona brought together twelve laboratories on five continents, including the Nice Institute of Physics (a joint CNRS / University of Nice Sophia Antipolis lab), to perform an unprecedented, collaborative, scientific experiment. By uniting approximately 100,000 people around the world with a video game, the researchers succeeded in both obviating the problem of data generation and rigorously validating their experimental observations regarding the violation of Bell’s inequalities. The results were published in Nature on 10 May 2018.

In physics, the principle of local realism requires that two, distant objects can only have limited correlations: events experienced by one of the two cannot be correlated to the other one beyond a certain extent. In the 1960s, John Stewart Bell formulated this limit between physical objects with mathematical inequalities. However, quantum objects do not obey this rule. In fact, events in between entangled quantum particles are correlated, regardless of their position in the universe. This observation violated Bell’s inequalities and thus the principle of local realism. To explain this phenomenon, conservative physicists at the beginning of the twentieth century – including Einstein – hypothesized that there are unknown physical parameters, which are of a form such that the constraint imposed by the inequalities would still be met.

Until today, researchers had only been able to show the violation of Bell’s inequalities by using data generated by quantum systems for their experiments. To test the correlation between entangled particles, it is necessary to observe each one in a random manner, without having the measurements of the two particles linked in any way. Random bit quantum generators allow this to be accomplished by giving instructions to observation instruments. This is a means to test quantum physics with a quantum system itself. To find a way out of this paradox, 100,000 people contributed to generating random bits by a non-quantum method. The data thereby created allowed the generation of a code to arbitrarily configure the instruments measuring the entangled particles in 13 experiments spread over 12 laboratories in as many countries.

To generate the bits, the participants were invited to play a video game: The BIG Bell Quest. The game asked players to randomly touch the numbers 1 and 0 on the keyboard. These bits were then sent directly to the laboratories. On 30 November 2016, the players generated more than 97 million bits, which continually supplied the experiments for 12 hours straight. During the game’s progression, the players could find explanations on scientific topics, such as details on Bell’s inequalities and the way they are tested. In addition, there were videos from the laboratories receiving the data.

The results obtained by the experiments confirm the violation of Bell’s inequalities using a more consistent and rigorous methodology than before and also open the way to furthering quantum applications in physics. The fundamental principles of quantum entanglement play an essential role in the development of quantum cryptography and quantum computing. The methodology used for the BIG Bell Test shows that participatory science has a place in fundamental physics.

• Sébastien Tanzilli -
• Challenging local realism with human randomness. The BIG Bell Test Collaboration, Nature, 10 May 2018, DOI:

Listen to the interview with Sébastien Tanzilli on France Culture on “Le journal des sciences”: