350,925 research outputs found

    Fourth Order Gradient Symplectic Integrator Methods for Solving the Time-Dependent Schr\"odinger Equation

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    We show that the method of splitting the operator eϵ(T+V){\rm e}^{\epsilon(T+V)} to fourth order with purely positive coefficients produces excellent algorithms for solving the time-dependent Schr\"odinger equation. These algorithms require knowing the potential and the gradient of the potential. One 4th order algorithm only requires four Fast Fourier Transformations per iteration. In a one dimensional scattering problem, the 4th order error coefficients of these new algorithms are roughly 500 times smaller than fourth order algorithms with negative coefficient, such as those based on the traditional Ruth-Forest symplectic integrator. These algorithms can produce converged results of conventional second or fourth order algorithms using time steps 5 to 10 times as large. Iterating these positive coefficient algorithms to 6th order also produced better converged algorithms than iterating the Ruth-Forest algorithm to 6th order or using Yoshida's 6th order algorithm A directly.Comment: 11 pages, 2 figures, submitted to J. Chem. Phy

    Electro-optic scanning of light coupled from a corrugated LiNbO3 waveguide

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    Light diffracted from a grating output coupler in a Ti-diffused LiNbO3 waveguide is scanned electro-optically. Using a coupling length of 2.5 mm in our arrangement we have demonstrated a scanning capability of one resolved spot per 3 V/µm applied field

    Mixed Qubit Cannot Be Universally Broadcast

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    We show that there does not exist any universal quantum cloning machine that can broadcast an arbitrary mixed qubit with a constant fidelity. Based on this result, we investigate the dependent quantum cloner in the sense that some parameter of the input qubit ρs(θ,ω,λ)\rho_s(\theta,\omega,\lambda) is regarded as constant in the fidelity. For the case of constant ω\omega, we establish the 121\to2 optimal symmetric dependent cloner with a fidelity 1/2. It is also shown that the 1M1\to M optimal quantum cloning machine for pure qubits is also optimal for mixed qubits, when λ\lambda is the unique parameter in the fidelity. For general NMN\to M broadcasting of mixed qubits, the situation is very different.Comment: 5 pages, Revte

    Study of free-piston Stirling engine driven linear alternators

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    The analysis, design and operation of single phase, single slot tubular permanent magnet linear alternator is presented. Included is the no-load and on-load magnetic field investigation, permanent magnet's leakage field analysis, parameter identification, design guidelines and an optimal design of a permanent magnet linear alternator. For analysis of the magnetic field, a simplified magnetic circuit is utilized. The analysis accounts for saturation, leakage and armature reaction
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