Roger Colbeck

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In classical and quantum information theory, operational quantities such as the amount of randomness that can be extracted from a given source or the amount of space needed to store given data are normally characterized by one of two entropy measures, called smooth min-entropy and smooth max-entropy, respectively. While both entropies are equal to the von(More)
The classical asymptotic equipartition property is the statement that, in the limit of a large number of identical repetitions of a random experiment, the output sequence is virtually certain to come from the typical set, each member of which is almost equally likely. In this paper, a fully quantum generalization of this property is shown, where both the(More)
According to quantum theory, measurements generate random outcomes, in stark contrast with classical mechanics. This raises the question of whether there could exist an extension of the theory that removes this indeterminism, as suspected by Einstein, Podolsky and Rosen. Although this has been shown to be impossible, existing results do not imply that the(More)
New channel coding converse and achievability bounds are derived for a single use of an arbitrary channel. Both bounds are expressed using a quantity called the “smooth 0-divergence”, which is a generalization of Rényi's divergence of order 0. The bounds are also studied in the limit of large block-lengths. In particular, they combine(More)
It was shown by Bell that no local hidden variable model is compatible with quantum mechanics. If, instead, one permits the hidden variables to be entirely nonlocal, then any quantum mechanical predictions can be recovered. In this Letter, we consider general hidden variable models which can have both local and nonlocal parts. We show the existence of(More)
Jonathan Barrett, ∗ Roger Colbeck, † and Adrian Kent 4, ‡ Royal Holloway, University of London, Egham Hill, Egham TW20 0EX, U.K. Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland. Centre for Quantum Information and Foundations, DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA, U.K.(More)
Uncertainty relations provide constraints on how well the outcomes of incompatible measurements can be predicted, and as well as being fundamental to our understanding of quantum theory, they have practical applications such as for cryptography and witnessing entanglement. Here we shed new light on the entropic form of these relations, showing that they(More)
Device-independent quantum cryptographic schemes aim to guarantee security to users based only on the output statistics of any components used, and without the need to verify their internal functionality. Since this would protect users against untrustworthy or incompetent manufacturers, sabotage, or device degradation, this idea has excited much interest,(More)
Wilms' tumour, or nephroblastoma, is the commonest renal neoplasm found in children, but is rarely found in adults, the world literature recording only approximately 200 cases. Individual case reports continue to be published but only within the last 10 years have definitive treatment regimes been suggested. In order to determine the UK experience of adult(More)