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  1. Einstein, Incompleteness, and the Epistemic View of Quantum States.Nicholas Harrigan & Robert W. Spekkens - 2010 - Foundations of Physics 40 (2):125-157.
    Does the quantum state represent reality or our knowledge of reality? In making this distinction precise, we are led to a novel classification of hidden variable models of quantum theory. We show that representatives of each class can be found among existing constructions for two-dimensional Hilbert spaces. Our approach also provides a fruitful new perspective on arguments for the nonlocality and incompleteness of quantum theory. Specifically, we show that for models wherein the quantum state has the status of something real, (...)
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    Evidence for the Epistemic View of Quantum States: A Toy Theory.Robert W. Spekkens - 2007 - Physical Review A 75:032110.
    We present a toy theory that is based on a simple principle: the number of questions about the physical state of a system that are answered must always be equal to the number that are unanswered in a state of maximal knowledge. Many quantum phenomena are found to have analogues within this toy theory. These include the noncommutativity of measurements, interference, the multiplicity of convex decompositions of a mixed state, the impossibility of discriminating nonorthogonal states, the impossibility of a universal (...)
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    The Inflation Technique for Causal Inference with Latent Variables.Elie Wolfe, Robert W. Spekkens & Tobias Fritz - 2019 - Journal of Causal Inference 7 (2).
    The problem of causal inference is to determine if a given probability distribution on observed variables is compatible with some causal structure. The difficult case is when the causal structure includes latent variables. We here introduce the inflation technique for tackling this problem. An inflation of a causal structure is a new causal structure that can contain multiple copies of each of the original variables, but where the ancestry of each copy mirrors that of the original. To every distribution of (...)
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    Picturing Classical and Quantum Bayesian Inference.Bob Coecke & Robert W. Spekkens - 2012 - Synthese 186 (3):651 - 696.
    We introduce a graphical framework for Bayesian inference that is sufficiently general to accommodate not just the standard case but also recent proposals for a theory of quantum Bayesian inference wherein one considers density operators rather than probability distributions as representative of degrees of belief. The diagrammatic framework is stated in the graphical language of symmetric monoidal categories and of compact structures and Frobenius structures therein, in which Bayesian inversion boils down to transposition with respect to an appropriate compact structure. (...)
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    The Status of Determinism in Proofs of the Impossibility of a Noncontextual Model of Quantum Theory.Robert W. Spekkens - 2014 - Foundations of Physics 44 (11):1125-1155.
    In order to claim that one has experimentally tested whether a noncontextual ontological model could underlie certain measurement statistics in quantum theory, it is necessary to have a notion of noncontextuality that applies to unsharp measurements, i.e., those that can only be represented by positive operator-valued measures rather than projection-valued measures. This is because any realistic measurement necessarily has some nonvanishing amount of noise and therefore never achieves the ideal of sharpness. Assuming a generalized notion of noncontextuality that applies to (...)
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