Robert W. Spekkens

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A controversy that has arisen many times over in disparate contexts is whether quantum co-herences between eigenstates of certain quantities are fact or fiction. We present a pedagogical introduction to the debate in the form of a hypothetical dialogue between proponents from each of the two camps: a factist and a fictionist. A resolution of the debate can(More)
Received (received date) Revised (revised date) It is well known that no quantum bit commitment protocol is unconditionally secure. Nonetheless, there can be non-trivial upper bounds on both Bob's probability of correctly estimating Alice's commitment and Alice's probability of successfully unveiling whatever bit she desires. In this paper, we seek to(More)
Recently, there has been much interest in a new kind of " unspeakable " quantum information that stands to regular quantum information in the same way that a direction in space or a moment in time stands to a classical bit string: the former can only be encoded using particular degrees of freedom while the latter are indifferent to the physical nature of(More)
The Kochen-Specker theorem demonstrates that it is not possible to reproduce the predictions of quantum theory in terms of a hidden variable model where the hidden variables assign a value to every projector deterministically and noncontextually. A noncontextual value assignment to a projector is one that does not depend on which other projectors-the(More)
Extended abstract for the article " A quantum advantage for inferring causal structure " , Nature Physics (2015) [9]. Causal explanations are a singularly useful way of organizing one's knowledge about the world. This has long been recognized by philosophers and, in recent decades, motivated the development of a rigorous mathematical framework, which proved(More)
Many seemingly paradoxical effects are known in the predictions for outcomes of measurements made on pre-and post-selected quantum systems. A class of such effects, which we call " logical pre-and post-selection paradoxes " , bear a striking resemblance to proofs of the Bell-Kochen-Specker theorem, which suggests that they demonstrate the contextuality of(More)
To make precise the sense in which nature fails to respect classical physics, one requires a formal notion of classicality. Ideally, such a notion should be defined operationally, so that it can be subject to direct experimental test, and it should be applicable in a wide variety of experimental scenarios so that it can cover the breadth of phenomena(More)