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In classical and quantum information theory, operational quantities such as the amount of ran-domness 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)

— New channel coding converse and achievability bounds are derived. Both bounds are expressed using a quantity called the " smooth 0-divergence ". As the block-length tends to infinity and the error probability is required to tend to zero, the bounds coincide to give a capacity formula which is equivalent to the one derived by Verdú and Han.

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)

Device-independent quantum key distribution is the task of using uncharacterized quantum devices to establish a shared key between two users. If a protocol is secure regardless of the device behaviour, it can be used to generate a shared key even if the supplier of the devices is malicious. To date, all device-independent quantum key distribution protocols… (More)

- Roger Colbeck
- 2007

We present attacks that show that unconditionally secure two-party classical computation is impossible for many classes of function. Our analysis applies to both quantum and relativistic protocols. We illustrate our results by showing the impossibility of oblivious transfer.

Alice is a charismatic quantum cryptographer who believes her parties are unmissable; Bob is a 1 glamorous string theorist who believes he is an indispensable guest. To prevent possibly traumatic collisions of self-perception and reality, their social code requires that decisions about invitation or acceptance be made via a cryptographically secure variable… (More)

- Stefan Wolf, Prof, Artur Ekert, Renato Renner, Daniel Burgarth, Roger Colbeck +30 others
- 2010

2010 ii Acknowledgments This thesis would never have been possible without the support of many people. First of all I would like to thank Stefan Wolf who has been a great advisor, giving us a lot of freedom in our research. Still, his door was always open for discussions. I would like to thank Renato Renner for an intense and fruitful collaboration which… (More)

- Matthew Saul Leifer, Klaas Landsman, Roger Colbeck, Terry Rudolph
- 2014

T owards the end of 2011, Pusey, Barrett and Rudolph derived a theorem that aimed to show that the quantum state must be ontic (a state of reality) in a broad class of realist approaches to quantum theory. This result attracted a lot of attention and controversy. The aim of this review article is to review the background to the Pusey–Barrett– Rudolph… (More)

- Raban Iten, Roger Colbeck, Ivan Kukuljan, Jonathan Home, Matthias Christandl
- 2015

—Every quantum operation can be decomposed into a sequence of single-qubit and Controlled-NOT (C-NOT) gates. In many implementations, single-qubit gates are simpler to perform than C-NOTs, and it is hence desirable to minimize the number of C-NOT gates required to implement a circuit. Previous work has looked at C-NOT-efficient synthesis of arbitrary… (More)