Robert W. Spekkens

Learn More
We present a quantum protocol for the task of weak coin flipping. We find that, for one choice of parameters in the protocol, the maximum probability of a dishonest party winning the coin flip if the other party is honest is 1/sqrt[2]. We also show that if parties restrict themselves to strategies wherein they cannot be caught cheating, their maximum(More)
Gilad Gour, 2, ∗ Markus P. Müller, 4, † Varun Narasimhachar, 5, ‡ Robert W. Spekkens, § and Nicole Yunger Halpern 6, ¶ Institute for Quantum Science and Technology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4 Department of Mathematics and Statistics, University of Calgary, 2500 University Drive NW, Calgary, Alberta,(More)
Quantum theory can be viewed as a generalization of classical probability theory, but the analogy as it has been developed so far is not complete. Whereas the manner in which inferences are made in classical probability theory is independent of the causal relation that holds between the conditioned variable and the conditioning variable, in the conventional(More)
We show that communication without a shared reference frame is possible using entangled states. Both classical and quantum information can be communicated with perfect fidelity without a shared reference frame at a rate that asymptotically approaches one classical bit or one encoded qubit per transmitted qubit. We present an optical scheme to communicate(More)
Two notions of nonclassicality that have been investigated intensively are: (i) negativity, that is, the need to posit negative values when representing quantum states by quasiprobability distributions such as the Wigner representation, and (ii) contextuality, that is, the impossibility of a noncontextual hidden variable model of quantum theory. Although(More)
Stephen D. Bartlett, Terry Rudolph, 3 and Robert W. Spekkens School of Physics, The University of Sydney, Sydney, New South Wales 2006, Australia Optics Section, Blackett Laboratory, Imperial College London, London SW7 2BW, United Kingdom Institute for Mathematical Sciences, Imperial College London, London SW7 2BW, United Kingdom Department of Applied(More)
Noether's theorem is a fundamental result in physics stating that every symmetry of the dynamics implies a conservation law. It is, however, deficient in several respects: for one, it is not applicable to dynamics wherein the system interacts with an environment; furthermore, even in the case where the system is isolated, if the quantum state is mixed then(More)