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Author |
Lydersen, Lars; Wiechers, Carlos; Wittmann, Christoffer; Elser, Dominique; Skaar, Johannes; Makarov, Vadim |
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Title |
Hacking commercial quantum cryptography systems by tailored bright illumination |
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2010 |
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Nature Photonics |
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Nat. Photon. |
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4 |
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10 |
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686 - 689 |
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quantum cryptography, hacking, QKD, APD |
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The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination. This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built of off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photodiodes to detect single photons. We believe that our findings are crucial for strengthening the security of practical QKD, by identifying and patching technological deficiencies. |
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RPLAB @ gujma @ |
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657 |
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Zhang, Qiang; Goebel, Alexander; Wagenknecht, Claudia; Chen, Yu-Ao; Zhao, Bo; Yang, Tao; Mair, Alois; Schmiedmayer, Jörg; Pan, Jian-Wei |
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Title |
Experimental quantum teleportation of a two-qubit composite system |
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Journal Article |
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Year |
2006 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
2 |
Issue |
10 |
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678-682 |
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fromIPMRAS; quantum teleportation |
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Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic or ionic qubits. However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation. Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols |
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RPLAB @ gujma @ |
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795 |
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Prevedel, Robert; Hamel, Deny R.; Colbeck, Roger; Fisher, Kent; Resch, Kevin J. |
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Title |
Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement |
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Journal Article |
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2011 |
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Nature Physics |
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Nat. Phys. |
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Volume |
7 |
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10 |
Pages |
757-761 |
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fromIPMRAS |
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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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Author |
Fuchs, G. D.; Burkard, G.; Klimov, P. V.; Awschalom, D. D. |
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Title |
A quantum memory intrinsic to single nitrogen–vacancy centres in diamond |
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Journal Article |
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Year |
2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
Issue |
10 |
Pages |
789-793 |
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fromIPMRAS |
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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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no |
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RPLAB @ gujma @ |
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823 |
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Author |
Hosseini, M.; Campbell, G.; Sparkes, B. M.; Lam, P. K.; Buchler, B. C. |
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Title |
Unconditional room-temperature quantum memory |
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Journal Article |
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Year |
2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
Issue |
10 |
Pages |
794-798 |
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Keywords |
fromIPMRAS |
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Abstract |
Just as classical information systems require buffers and memory, the same is true for quantum information systems. The potential that optical quantum information processing holds for revolutionizing computation and communication is therefore driving significant research into developing optical quantum memory. A practical optical quantum memory must be able to store and recall quantum states on demand with high efficiency and low noise. Ideally, the platform for the memory would also be simple and inexpensive. Here, we present a complete tomographic reconstruction of quantum states that have been stored in the ground states of rubidium in a vapour cell operating at around 80 °C. Without conditional measurements, we show recall fidelity up to 98% for coherent pulses containing around one photon. To unambiguously verify that our memory beats the quantum no-cloning limit we employ state-independent verification using conditional variance and signal-transfer coefficients. |
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RPLAB @ gujma @ |
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824 |
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Arcizet, O.; Jacques, V.; Siria, A.; Poncharal, P.; Vincent, P.; Seidelin, S. |
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Title |
A single nitrogen-vacancy defect coupled to a nanomechanical oscillator |
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Journal Article |
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2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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7 |
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11 |
Pages |
879-883 |
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fromIPMRAS |
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We position a single nitrogen-vacancy (NV) centre hosted in a diamond nanocrystal at the extremity of a SiC nanowire. This novel hybrid system couples the degrees of freedom of two radically different systems: a nanomechanical oscillator and a single quantum object. We probe the dynamics of the nano-resonator through time-resolved nanocrystal fluorescence and photon-correlation measurements, conveying the influence of a mechanical degree of freedom on a non-classical photon emitter. Moreover, by immersing the system in a strong magnetic field gradient, we induce a magnetic coupling between the nanomechanical oscillator and the NV electronic spin, providing nanomotion readout through a single electronic spin. Spin-dependent forces inherent to this coupling scheme are essential in a variety of active cooling and entanglement protocols used in atomic physics, and should now be within the reach of nanomechanical hybrid systems. |
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RPLAB @ gujma @ |
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819 |
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Author |
Saffman, Mark |
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Title |
Quantum computing: A quantum telecom link |
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Journal Article |
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2010 |
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Nature Physics |
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Nat. Phys. |
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6 |
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11 |
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838-839 |
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fromIPMRAS |
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Converting data-carrying photons to telecommunication wavelengths enables distribution of quantum information over long distances. |
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RPLAB @ gujma @ |
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833 |
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Author |
Raussendorf, Robert |
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Title |
Quantum computing: Shaking up ground states |
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2010 |
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Nature Physics |
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Nat. Phys. |
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Volume |
6 |
Issue |
11 |
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840-841 |
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fromIPMRAS |
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Measurement-based quantum computation with an Affleck-Kennedy-Lieb-Tasaki state is experimentally realized for the first time. |
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RPLAB @ gujma @ |
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834 |
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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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fromIPMRAS |
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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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RPLAB @ gujma @ |
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778 |
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Trabesinger, Andreas |
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Quantum mechanics: Shaken foundations |
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2009 |
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Nature Physics |
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Nat. Phys. |
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5 |
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12 |
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863 |
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RPLAB @ gujma @ |
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802 |
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