3 research outputs found

    Minimal measurements of the gate fidelity of a qudit map

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    We obtain a simple formula for the average gate fidelity of a linear map acting on qudits. It is given in terms of minimal sets of pure state preparations alone, which may be interesting from the experimental point of view. These preparations can be seen as the outcomes of certain minimal positive operator valued measures. The connection of our results with these generalized measurements is briefly discussed

    Effect of noise on geometric logic gates for quantum computation

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    We introduce the non-adiabatic, or Aharonov-Anandan, geometric phase as a tool for quantum computation and show how it could be implemented with superconducting charge qubits. While it may circumvent many of the drawbacks related to the adiabatic (Berry) version of geometric gates, we show that the effect of fluctuations of the control parameters on non-adiabatic phase gates is more severe than for the standard dynamic gates. Similarly, fluctuations also affect to a greater extent quantum gates that use the Berry phase instead of the dynamic phase.Comment: 8 pages, 4 figures; published versio

    State transfer in dissipative and dephasing environments

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    By diagonalization of a generalized superoperator for solving the master equation, we investigated effects of dissipative and dephasing environments on quantum state transfer, as well as entanglement distribution and creation in spin networks. Our results revealed that under the condition of the same decoherence rate Îł\gamma, the detrimental effects of the dissipative environment are more severe than that of the dephasing environment. Beside this, the critical time tct_c at which the transfer fidelity and the concurrence attain their maxima arrives at the asymptotic value t0=π/2λt_0=\pi/2\lambda quickly as the spin chain length NN increases. The transfer fidelity of an excitation at time t0t_0 is independent of NN when the system subjects to dissipative environment, while it decreases as NN increases when the system subjects to dephasing environment. The average fidelity displays three different patterns corresponding to N=4r+1N=4r+1, N=4r−1N=4r-1 and N=2rN=2r. For each pattern, the average fidelity at time t0t_0 is independent of rr when the system subjects to dissipative environment, and decreases as rr increases when the system subjects to dephasing environment. The maximum concurrence also decreases as NN increases, and when N→∞N\rightarrow\infty, it arrives at an asymptotic value determined by the decoherence rate Îł\gamma and the structure of the spin network.Comment: 12 pages, 6 figure
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