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Author (up) Pirandola, Stefano; Mancini, Stefano; Lloyd, Seth; Braunstein, Samuel L.
Title Continuous-variable quantum cryptography using two-way quantum communication Type Journal Article
Year 2008 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 4 Issue 9 Pages 726-730
Keywords fromIPMRAS
Abstract Quantum cryptography has recently been extended to continuous-variable systems, such as the bosonic modes of the electromagnetic field possessing continuous degrees of freedom. In particular, several cryptographic protocols have been proposed and experimentally implemented using bosonic modes with Gaussian statistics. These protocols have shown the possibility of reaching very high secret key rates, even in the presence of strong losses in the quantum communication channel. Despite this robustness to loss, their security can be affected by more general attacks where extra Gaussian noise is introduced by the eavesdropper. Here, we show a `hardware solution' for enhancing the security thresholds of these protocols. This is possible by extending them to two-way quantum communication where subsequent uses of the quantum channel are suitably combined. In the resulting two-way schemes, one of the honest parties assists the secret encoding of the other, with the chance of a non-trivial superadditive enhancement of the security thresholds. These results should enable the extension of quantum cryptography to more complex quantum communications.
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Call Number RPLAB @ gujma @ Serial 798
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Author (up) Prevedel, Robert; Hamel, Deny R.; Colbeck, Roger; Fisher, Kent; Resch, Kevin J.
Title Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 10 Pages 757-761
Keywords fromIPMRAS
Abstract Heisenberg's uncertainty principle provides a fundamental limitation on the ability of an observer holding classical information to predict the outcome when one of two measurements is performed on a quantum system. However, an observer with access to a particle (stored in a quantum memory) which is entangled with the system generally has a reduced uncertainty: indeed, if the particle and system are maximally entangled, the observer can perfectly predict the outcome of whichever measurement is chosen. This effect has recently been quantified in a new entropic uncertainty relation. Here we experimentally investigate this relation, showing its effectiveness as an efficient entanglement witness. We use entangled photon pairs, an optical delay line serving as a simple quantum memory and fast, active feed-forward. Our results quantitatively agree with the new uncertainty relation. Our technique acts as a witness for almost all entangled states in our experiment as we obtain lower uncertainties than would be possible without the entangled particle.
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Call Number RPLAB @ gujma @ Serial 821
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Author (up) Raussendorf, Robert
Title Quantum computing: Shaking up ground states Type Journal Article
Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 6 Issue 11 Pages 840-841
Keywords fromIPMRAS
Abstract Measurement-based quantum computation with an Affleck-Kennedy-Lieb-Tasaki state is experimentally realized for the first time.
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Call Number RPLAB @ gujma @ Serial 834
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Author (up) Saffman, Mark
Title Quantum computing: A quantum telecom link Type Journal Article
Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 6 Issue 11 Pages 838-839
Keywords fromIPMRAS
Abstract Converting data-carrying photons to telecommunication wavelengths enables distribution of quantum information over long distances.
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Call Number RPLAB @ gujma @ Serial 833
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Author (up) Shor, Peter W.
Title Quantum information theory: The bits don't add up Type Journal Article
Year 2009 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 5 Issue Pages 247 - 248
Keywords fromIPMRAS
Abstract A counterexample to the 'additivity question', the most celebrated open problem in the mathematical theory of quantum information, casts doubt on the possibility of finding a simple expression for the information capacity of a quantum channel.
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Call Number RPLAB @ gujma @ Serial 800
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