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Pirandola, Stefano; Mancini, Stefano; Lloyd, Seth; Braunstein, Samuel L. |
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Continuous-variable quantum cryptography using two-way quantum communication |
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2008 |
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Nature Physics |
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Nat. Phys. |
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4 |
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9 |
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726-730 |
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fromIPMRAS |
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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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798 |
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Author |
Capmany, José; Gasulla, Ivana; Sales, Salvador |
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Title |
Microwave photonics: Harnessing slow light |
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2011 |
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Nature Photonics |
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Nat. Photon. |
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5 |
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12 |
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731-733 |
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Slow-light techniques originally conceived for buffering high-speed digital optical signals now look set to play an important role in providing broadband phase and true time delays for microwave signals. |
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778 |
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Hannay, Timo |
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A new kind of science? |
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2011 |
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Nature Physics |
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Nat. Phys. |
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7 |
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742 |
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818 |
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Prevedel, Robert; Hamel, Deny R.; Colbeck, Roger; Fisher, Kent; Resch, Kevin J. |
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Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement |
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2011 |
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Nature Physics |
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Nat. Phys. |
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7 |
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10 |
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757-761 |
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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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RPLAB @ gujma @ |
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821 |
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Fuchs, G. D.; Burkard, G.; Klimov, P. V.; Awschalom, D. D. |
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A quantum memory intrinsic to single nitrogen–vacancy centres in diamond |
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2011 |
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Nature Physics |
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Nat. Phys. |
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7 |
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10 |
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789-793 |
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A quantum memory, composed of a long-lived qubit coupled to each processing qubit, is important to building a scalable platform for quantum information science. These two qubits should be connected by a fast and high-fidelity operation to store and retrieve coherent quantum states. Here, we demonstrate a room-temperature quantum memory based on the spin of the nitrogen nucleus intrinsic to each nitrogen–vacancy (NV) centre in diamond. We perform coherent storage of a single NV centre electronic spin in a single nitrogen nuclear spin using Landau–Zener transitions across a hyperfine-mediated avoided level crossing. By working outside the asymptotic regime, we demonstrate coherent state transfer in as little as 120 ns with total storage fidelity of 88±6%. This work demonstrates the use of a quantum memory that is compatible with scaling as the nitrogen nucleus is deterministically present in each NV centre defect. |
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RPLAB @ gujma @ |
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823 |
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