A little quantum mechanics could provide an edge in the classic card game bridge, a team of physicists claims. Bridge is played by four people in teams of two, and the goal of the game is in part to deduce which cards your partner and your opponents hold. Players do this during bridge's pivotal bidding phase, by making terse bids such as "three hearts." The physicists wondered if the quantum world could help players convey more information without breaking bridge's stringent communication rules. This month in Physical Review X, the team presents a thought experiment in which each player receives an identical photon from an entangled pair. In such a pair, the state of each photon—say, the direction in which it’s polarized—is completely unknown, but is strongly correlated with the state of the other photon. So if one player, Alice, measures the polarization of her photon, she can instantly deduce what Bob will see when he measures his photon. Alice and Bob can then use that correlation in concert with their regular bids to better suss out each other's hand, the physicists find. The team found that the extra flexibility gave players a game-changing 2% advantage over their competition. The scheme does not break the current rules of bridge, but it would likely require a lab full of optical equipment.
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