Quantum mechanics is compatible with scenarios where the relative order between two events can be indefinite. Here we show that two independent instances of a noisy process can behave as a perfect quantum communication channel when used in a coherent superposition of two alternative orders. This phenomenon occurs even if the original process has zero capacity to transmit quantum information. In contrast, perfect quantum communication does not occur when the message is sent directly from the sender to the receiver through a superposition of alternative paths, with an independent noise process acting on each path. The possibility of perfect quantum communication through independent noisy channels highlights a fundamental difference between the superposition of orders in time and the superposition of paths in space.

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Interesting connection has been established between two apparently unrelated concepts, namely, quantum nonlocality and Bayesian game theory. It has been shown that nonlocal correlations in the form of advice can outperform classical equilibrium strategies in common interest Bayesian games and also in conflicting interest games. However, classical equilibrium strategies can be of two types, fair and unfair. Whereas in fair equilibrium payoffs of different players are same, in unfair case they differ. Advantage of nonlocal correlation has been demonstrated over fair strategies. In this work we show that quantum strategies can outperform even the unfair classical equilibrium strategies. For this purpose we consider a class of two players games which as a special case includes the conflicting game proposed in [Phys. Rev. Lett. 114, 020401 (2015)]. These games can have both fair and unfair classical equilibria and also can have only unfair ones. We provide a simple analytic characterization of the nonlocal correlations that are advantageous over the classical equilibrium strategies in these games.Undoubtedly one of the most fundamental contradictions of Quantum mechanics (QM) with classical physics gets manifested in its nonlocal behavior. This bizarre feature of QM was first established in the seminal work of J. S. Bell [1], where he has shown that QM is incompatible with the local-realistic world view of classical physics. More precisely, Bell showed that measurement statistics of multipartite entangled quantum systems can violate an empirically testable local realistic inequality (in general called Bell type inequalities) which establishes the denial of local realism underlying QM. Since Bell's work, nonlocality remains at the center of quantum foundational research (see [2] and references therein) and it has been verified in numerous successful experiments, starting from the famous Aspect's experiment [3] to very recent loop-hole free tests [4]. Apart from foundational interest quantum nonlocal correlations have been proved to be the key resource in various device-independent protocols [5]. Very recently Brunner and Linden have established that Bell nonlocality has interesting connection with a seemingly different area of research, namely, theory of Bayesian game [6]. A Bayesian game can be played under classical equilibrium strategies which are of two types, fair equilibria and unfair equilibria. Whereas in fair equilibria payoffs of different parties are same, in unfair equilibria they differ. It has been shown that QM can provide advantageous strategies over the best classical strategies in common interest Bayesian games [6] and can also outperform the fair classical equilibrium strategies in conflicting games [7]. The aim of this present paper is to study whether nonlocal correlation can be advantageous over the classical unfair equilibrium strategies in such a games.Operationally Bell type inequalities can be best understood in terms of games involving several number of spatially separated parties. Each part...

Presence of correlations among the constituent quantum systems has a great relevance in thermodynamics. Significant efforts have been devoted to investigate the role of correlations in work extraction, among others. Here, we derive a bound on the difference between global and local extractable work by unitary operations (ergotropic gap), for bipartite separable states. Violation of this bound necessarily certifies the presence of entanglement. This gap is shown to be a monotone under LOCC assisted state transformations for pure bipartite quantum states. Our criterion has an implication in witnessing the dimension of a bipartite quantum state, with same local dimensions. On the other hand, our result gives an operational meaning to the Nielsen-Kempe disorder criterion. We also propose a schematic model to realize the separability bound experimentally and to detect entanglement for a restricted class of quantum states.

Quantum nonlocality without entanglement (Q-NWE) captures nonlocal behavior of multipartite product states as they may entail global operation for optimal decoding of the classical information encoded in the state ensemble that allows local preparation. In this Rapid Communication we show that the phenomena of NWE is not specific to quantum theory only, but rather a class of generalized probabilistic theories that can exhibit such behavior. In fact, several manifestations of NWE, e.g., asymmetric local discrimination, suboptimal local discrimination, the notion of separable but locally unimplementable measurements arise generically in operational theories other than quantum theory. We propose a framework to compare the strength of NWE in different theories and show that such behavior in quantum theory is limited, suggesting a specific topological feature of quantum theory, namely, the continuity of state space structure. Our work adds the erstwhile missing foundational appeal to the study of NWE phenomena along with its information-theoretic relevance.