59 research outputs found
The equivalence of Bell's inequality and the Nash inequality in a quantum game-theoretic setting
The interaction of competing agents is described by classical game theory. It
is now well known that this can be extended to the quantum domain, where agents
obey the rules of quantum mechanics. This is of emerging interest for exploring
quantum foundations, quantum protocols, quantum auctions, quantum cryptography,
and the dynamics of quantum cryptocurrency, for example. In this paper, we
investigate two-player games in which a strategy pair can exist as a Nash
equilibrium when the games obey the rules of quantum mechanics. Using a
generalized Einstein-Podolsky-Rosen (EPR) setting for two-player quantum games,
and considering a particular strategy pair, we identify sets of games for which
the pair can exist as a Nash equilibrium only when Bell's inequality is
violated. We thus determine specific games for which the Nash inequality
becomes equivalent to Bell's inequality for the considered strategy pair.Comment: 18 pages, revise
Belief-Invariant and Quantum Equilibria in Games of Incomplete Information
Drawing on ideas from game theory and quantum physics, we investigate
nonlocal correlations from the point of view of equilibria in games of
incomplete information. These equilibria can be classified in decreasing power
as general communication equilibria, belief-invariant equilibria and correlated
equilibria, all of which contain the familiar Nash equilibria. The notion of
belief-invariant equilibrium has appeared in game theory before, in the 1990s.
However, the class of non-signalling correlations associated to
belief-invariance arose naturally already in the 1980s in the foundations of
quantum mechanics.
Here, we explain and unify these two origins of the idea and study the above
classes of equilibria, and furthermore quantum correlated equilibria, using
tools from quantum information but the language of game theory. We present a
general framework of belief-invariant communication equilibria, which contains
(quantum) correlated equilibria as special cases. It also contains the theory
of Bell inequalities, a question of intense interest in quantum mechanics, and
quantum games where players have conflicting interests, a recent topic in
physics.
We then use our framework to show new results related to social welfare.
Namely, we exhibit a game where belief-invariance is socially better than
correlated equilibria, and one where all non-belief-invariant equilibria are
socially suboptimal. Then, we show that in some cases optimal social welfare is
achieved by quantum correlations, which do not need an informed mediator to be
implemented. Furthermore, we illustrate potential practical applications: for
instance, situations where competing companies can correlate without exposing
their trade secrets, or where privacy-preserving advice reduces congestion in a
network. Along the way, we highlight open questions on the interplay between
quantum information, cryptography, and game theory
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