HomePhysicsFirst experiment of quantum contextuality 'without loopholes'

First experiment of quantum contextuality ‘without loopholes’

Contextuality is essential to explain the power of quantum computers. It is also essential for the security of quantum communications. The study was published in the journal Science Advances.

Scientists have used a game to explain this. Sergio and Mario show us their hands with their fists clenched. We ask them to open one hand each for a moment. We check whether the hand contains something or not. In each round of the game, we can ask to open the same hand as many times as we want.

After playing many rounds, the hand that Sergio has opened either always has something in it or is always empty. The same goes for Mario. If we assume that, Sergio and Mario have or do not have something in each of their hands, it can be shown that the sum of certain probabilities has a limit. If we call this sum S, S cannot be greater than 2. However, in our experiment, S is 2.5.

Here Sergio is an ytterbium ion and Mario is a barium ion. An ion is an electrically charged atom. The two ions are caught in a trap and different lasers are used to make the measurements. In quantum physics, systems have no properties when they are not measured.

This experiment is very important because it is the first time that, questions to Sergio do not alter Mario’s answers and vice versa. When using ions, Sergio and Mario always respond. In other experiments, they sometimes do not respond. We can repeat the measurements in any order we wish.

It is a unique experiment that allows us to prove that everything happens exactly as quantum physics predicts. The fact that we have such precise control over such sensitive systems shows how far we have come. The phenomenon shown in the experiment is what physicists refer to as “contextuality”. It is behind the power of quantum computers to solve problems impossible for today’s computers.


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