University of Bristol Quantum Computation & Information Group

Dr Marcin Pawlowski
Department of Mathematics
University of Bristol
University Walk
Bristol BS8 1TW, U.K.
Fax: +44(0)117 928-7999
Email: dokmpa (at)
Recent publications:

  • Reply to "Comment on 'Security proof for cryptographic protocols based only on the monogamy of Bell's inequality violations' "
    M. Pawlowski
    30 May 2012

    In this reply I address the comment by W-Y. Hwang and O. Gittsovich on my paper [Phys. Rev. A {\bf 82}, 032313 (2010)]. The authors of the comment point out that I use implicit assumption that the alphabet of the eavesdropper is binary. They claim that such assumption is unrealistic. Here I show that even without this assumption the main result of my paper still holds.
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  • From Qubits to Hyperbits
    M. Pawlowski, A. Winter
    14 June 2011

    We propose to study `hyperbits' as generalizations of quantum bits: their state spaces are d-dimensional Euclidean balls (d=3 is the Bloch sphere of qubits), while they can be subjected to binary measurements corresponding to any direction in d-dimensional Euclidean space. We show that sending and using one hyperbit from one player to another one is in a certain sense equivalent to sharing arbitrary entanglement and sending 1 classical bit -- at least in the context of certain non-local games. We also demonstrate a fundamental identity for hyperbits, limiting their information processing capabilities. As a consequence, we prove a stronger form of the Information Causality inequality for messages of 1 bit; it encapsulates not only the known information limitations of quantum theory but also complementarity.
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  • Semi-device-independent security of one-way quantum key distribution
    Marcin Pawlowski, Nicolas Brunner
    22 March 2011

    By testing nonlocality, the security of entanglement-based quantum key distribution (QKD) can be enhanced to being 'device-independent'. Here we ask whether such a strong form of security could also be established for one-way QKD. While fully device-independent security is impossible, we show that security can be guaranteed against collective attacks in a semi-device-independent scenario. In the latter, the devices used by the trusted parties are non-characterized, but the dimensionality of the quantum systems used in the protocol is assumed to be bounded. Our security proof relies on the analogies between one-way QKD, dimension witnesses and random-access codes.
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  • Recovering part of the quantum boundary from information causality
    Jonathan Allcock, Nicolas Brunner, Marcin Pawlowski, Valerio Scarani
    19 June 2009
    Phys. Rev. A 80, 040103(R) (2009)

    Recently, the principle of information causality has appeared as a good candidate for an information-theoretic principle that would single out quantum correlations among more general non-signalling models. Here we present results going in this direction; namely we show that part of the boundary of quantum correlations actually emerges from information causality.
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  • A new physical principle: Information Causality
    M. Pawlowski, T. Paterek, D. Kaszlikowski, V. Scarani, A. Winter, M. Zukowski
    15 May 2009
    Nature 461, 1101 (2009)

    Quantum physics exhibits many remarkable features. For example, it gives probabilistic predictions (non-determinism), does not allow copying of unknown states (no-cloning), its correlations are stronger than any classical correlations but information cannot be transmitted faster than light (no-signaling). However, all the mentioned features do not single out quantum physics. A broad class of theories exist which share all of them with quantum mechanics and allow even stronger than quantum correlations. Here, we introduce the principle of Information Causality, stating that communication of m classical bits causes information gain of at most m bits. We show that this principle is respected both in classical and quantum physics, and that all stronger than quantum correlations violate it. We suggest that Information Causality, being a generalization of no-signaling, is one of the foundational properties of Nature.
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