## Science is one step closer to demonstrating “quantum pseudotelepathy” (and Spain has done its part)

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Quantum entanglement is one of the most curious phenomena in nature. As we have heard many times (every time someone refers to the famous Schrödinger’s cat) particles can exist in two states at the same time. Once we observe them, these particles begin to “collapse” or fold, that is, they decide on one state or another. Quantum entanglement occurs when two particles become connected in such a way that the “collapsed” state of one gives us information about the state of the other.

**Pseudotelepathy.**

Schrödinger’s cat thought experiment serves to give us an idea at the macroscopic level of this quantum phenomenon, but it is still a thought experiment. Quantum game theory, for its part, proposes cooperative games, similar to the prisoner’s dilemma made famous by John Nash, as a way to show that entangled particles can cooperate. The objective of this game is to demonstrate quantum pseudo-telepathy, the phenomenon by which these entangled particles appear (hence “pseudo”) to communicate and agree on strategies.

A team of researchers in China has used one of these quantum games to try to demonstrate this quantum pseudo-telepathy, and the results, published in the magazine *Physical Review Letters*they are positive.

**The magic square.**

The experiment is based on a proposal by the Spanish physicist Adán Cabello, which in turn is based on the game designed by David Mermin and Asher Peres, from whom it receives its name (Mermin-Peres). The dynamics of the game is simple: Alice and Bob (the names are a reference to other research on the subject) must fill in the boxes of a nine-box square (3×3) with one of two values, 1 or -1.

Alice must fill her box so that, multiplied by the cells of her rows, the result is always 1 (that is, 1,1,1 is a valid option as well as -1,1-1 and variations of this last combination) . Bob must fill in her square taking into account her columns, the result of multiplying the boxes by columns must always be -1 (that is, -1, -1, -1 or 1, -1,1 and similar combinations ).

a referee will take a row and a column of the players’ boxes. Alice and Bob win the game if, without communicating with each other, they fill in the box common to Alice’s row and Bob’s column with the same number.

**Win the game.**

If Alice and Bob were human beings, they could design a strategy that would lead them to win almost eight out of nine games, being able to build almost identical squares, but they must always be different in at least one square. This is where the work of Jia-Min Xu and his companions comes into play: using pseudo quantum telepathy Alice and Bob can exceed your expectations. Almost as if they communicated telepathically for real.

The key is in a principle derived from the quantum: nothing is until it is observed. The boxes that Alice and Bob fill in only come into existence when they are evaluated by the judge, and the values that appear in the row and column are linked. The rest of Alice and Bob’s boxes don’t even exist, because they are not observed.

**A step towards quantum computing.**

This experiment can open doors to quantum computing. For Anne Broadbent, from the University of Ottawa (who was not part of the team that carried out the study), for example, this experiment could be used to create programs that allow verifying the correct functioning of a quantum computer.

Xi-Lin Wang, for his part, stressed that the work would serve to “show the potential of our team’s favorite technology: photons entangled in polarization and angular momentum.” And it is that part of the success of the team was based on having made a double link of the same pair of photons (instead of the alternative, making a simple link of two pairs of photons).

**Without a lens that tells us the future.**

Putting experiments like this into practice is not an easy task, Cabello himself admitted. Quantum computing and related technologies such as quantum cryptography are making headlines thanks to the speed at which new discoveries are being produced. In any case, as usual, only time will tell the exact speed and direction in which these promising technologies are taking us.

Image | IBM, CC BY-ND 2.0

Quantum entanglement is one of the most curious phenomena in nature. As we have heard many times (every time someone…

Quantum entanglement is one of the most curious phenomena in nature. As we have heard many times (every time someone…