The Eisert way to play
The effect of entangling the initial state in the quantum version of the prisoner's dilemma game can be mimicked by including an additional quantum-mechanical strategy C to the pay-off matrix. As far as these three strategies are concerned, (C,C) is now a Nash equilibrium (purple box). Since no player can gain by lessening the others' pay-off, it is also Pareto optimal (green box). Hence the prisoner's dilemma is apparently resolved in the quantum world.