Games with incomplete information are formulated in a multi-sector probability matrix formalism that can cope with quantum as well as classical strategies. An analysis of classical and quantum strategy in a multi-sector extension of the game of Battle of Sexes clarifies the two distinct roles of nonlocal strategies, and establish the direct link between the true quantum gain of game's payoff and the breaking of Bell inequalities.KEYWORDS: quantum Harsanyi game, nonlocality, entanglement, battle of sexes
IntroductionAlthough Bell's inequalities 1, 2) are usually discussed in the context of quantum Bell experiments with spins and observers, they can be established in a far wider variety of settings. Here we bring one such example in a rather unexpected field of the theory of games of incomplete information.3) Game theory now occupies a central place in areas of applied mathematics, economics, sociology, and in mathematical biology. It is well known that Bell inequality can be broken only when the assumption of local realism is abandoned. This result, when considered in the context of game theory of incomplete information, links together the breaking of Bell inequality and the existence of nonlocal correlation between players. To explore this further, a consideration of quantum strategies 4-8) in games of incomplete information becomes both relevant and interesting.With rapid advancement of quantum information technologies, playing games with quantum resources is within the technical reach of advanced laboratories.9, 10) It is quite conceivable that playing games with quantum strategies, using properly coordinated quantum devices, becomes commonplace in the near future. It is therefore timely that we analyze the physical contents of quantum strategies, and examine the relevance of Bell inequality breaking. It is now generally agreed that quantum strategy can shift the classical outcome of the game in favor of all players, but how much of it is due to truly quantum effect, never achievable classically, is still under debate.11) Games with incomplete information synergetic to Bell experiment setup appears to be a good candidate to settle this issue, which is one of the basic unanswered question of quantum game theory.To study quantum strategies in games of incomplete information, we develop a formalism of game theory based on multi-sector probability matrix. We then analyze a game of incomplete information which is an extension of the well known game of Battle of Sexes and find the classical and the quantum Bayesian Nash equilibria. We find two distinct effects of quantum entanglement in games of incomplete information: