45,041 research outputs found

    Deterministic Controlled-NOT gate for single-photon two-qubit quantum logic

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    We demonstrate a robust implementation of a deterministic linear-optical Controlled-NOT (CNOT) gate for single-photon two-qubit quantum logic. A polarization Sagnac interferometer with an embedded 45^{\circ}-oriented dove prism is used to enable the polarization control qubit to act on the momentum (spatial) target qubit of the same photon. The CNOT gate requires no active stabilization because the two spatial modes share a common path, and it is used to entangle the polarization and momentum qubits.Comment: 10 pages, 4 figures. Typos corrected, referee comments and correction

    Attacking quantum key distribution with single-photon two-qubit quantum logic

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    The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual attack on Bennett-Brassard 1984 quantum key distribution (BB84 QKD) by means of a single controlled-NOT (CNOT) gate. This paper describes a complete physical simulation of the FPB-probe attack on polarization-based BB84 QKD using a deterministic CNOT constructed from single-photon two-qubit quantum logic. Adding polarization-preserving quantum nondemolition measurements of photon number to this configuration converts the physical simulation into a true deterministic realization of the FPB attack.Comment: 8 pages, 9 figures; references added, 1 new figure, appendix expanded; accepted for publication in Phys. Rev.

    Application of Pad\'{e} interpolation to stationary state problems

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    If the small and large coupling behavior of a physical system can be computed perturbatively and expressed respectively as power series in a coupling parameter gg and 1/g1/g, a Pad\'{e} approximant embracing the two series can interpolate between these two limits and provide an accurate estimate of the system's behavior in the generally intractable intermediate coupling regime. The methodology and validity of this approach are illustrated by considering several stationary state problems in quantum mechanics.Comment: RevTeX4, 7 pages (including 7 tables); v4 typos correcte

    Implementation of uniform perturbation method for potential flow past axisymmetric and two-dimensional bodies

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    The aerodynamic characteristics of potential flow past an axisymmetric slender body and a thin airfoil are calculated using a uniform perturbation analysis method. The method is based on the superposition of potentials of point singularities distributed inside the body. The strength distribution satisfies a linear integral equation by enforcing the flow tangency condition on the surface of the body. The complete uniform asymptotic expansion of its solution is obtained with respect to the slenderness ratio by modifying and adapting an existing technique. Results calculated by the perturbation analysis method are compared with the existing surface singularity panel method and some available analytical solutions for a number of cases under identical conditions. From these comparisons, it is found that the perturbation analysis method can provide quite accurate results for bodies with small slenderness ratio. The present method is much simpler and requires less memory and computation time than existing surface singularity panel methods of comparable accuracy
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