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Register a new userExploring the limits of no backward in time signalling
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We present an operational and model-independent framework to investigate the concept of no-backwards-in-time signaling. We define no-backwards-in-time signaling conditions, closely related to the spatial no-signaling conditions. These allow for theoretical possibilities in which the future affects the past, nevertheless without signaling backwards in time. This is analogous to non-local but no-signaling spatial correlations. Furthermore, our results shed new light on situations with indefinite causal structure and their connection to quantum theory.
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Steering is a physical phenomenon which is not restricted to quantum theory, it is also present in more general, no-signalling theories. Here, we study steering from the point of view of no-signalling theories. First, we show that quantum steering involves a collection of different aspects, which need to be separated when considering steering in no-signalling theories. By deconstructing quantum steering, we learn more about the nature of the steering phenomenon itself. Second, we introduce a new concept, that we call blind steering, which can be seen as the most basic form of steering, present both in quantum mechanics and no-signalling theories.
We show that non-local resources cannot be used for probabilistic signalling even if one can produce exact clones with the help of a probabilistic quantum cloning machine (PQCM). We show that PQCM cannot help to distinguish two statistical mixtures at a remote location. Thus quantum theory rules out the possibility of sending superluminal signals not only deterministically but also probabilistically. We give a bound on the success probability of producing multiple clones in an entangled system.
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It is known that if one could clone an arbitrary quantum state one could send signal faster than the speed of light. However it remains interesting to see that if one can perfectly self replicate an arbitrary quantum state, does it violate the no signalling principle? Here we see that perfect self replication would also lead to superluminal signalling.
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