Flip a coin in the quantum realm and the outcome won't be heads or tails. The quantum coin can also settle on heads and tails. The same holds true for a bit in a quantum computer, called a qubit. For this reason, scientists expect that quantum computers will be able to use entirely new algorithms to solve a variety of problems more efficiently than conventional machines. To test what these new approaches might look like, they are studying how the strategies of standard games change under quantum rules. In the September issue of Physical Review A, Patrick Hayden and his colleagues at the University of Oxford describe a quantum version of a typical Dilemma game, in which three players must decide whether to betray each other in the hope of increasing their own chances of winning.

Hayden and his team found that the players' strategies needed to be quite different in the quantum dilemma game. The scientists represented each player's approach with a qubit: the player could try to win (given a value of 0); they could settle for not winning (1); or they could try for some combination of the two. Because the qubits were entangled, or interlinked in way unique to quantum laws, the choices of each player heavily affected the others. And Hayden's group discovered that this entanglement actually removed the dilemma. In other words, it eliminated the incentive a player would have in the real world to betray his opponents