11 research outputs found

    Time-convolutionless reduced-density-operator theory of a noisy quantum channel: a two-bit quantum gate for quantum information processing

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    An exact reduced-density-operator for the output quantum states in time-convolutionless form was derived by solving the quantum Liouville equation which governs the dynamics of a noisy quantum channel by using a projection operator method and both advanced and retarded propagators in time. The formalism developed in this work is general enough to model a noisy quantum channel provided specific forms of the Hamiltonians for the system, reservoir, and the mutual interaction between the system and the reservoir are given. Then, we apply the formulation to model a two-bit quantum gate composed of coupled spin systems in which the Heisenberg coupling is controlled by the tunneling barrier between neighboring quantum dots. Gate Characteristics including the entropy, fidelity, and purity are calculated numerically for both mixed and entangled initial states

    Large dielectric constant and giant nonlinear conduction in the organic conductor theta-(BEDT-TTF)_2CsZn(SCN)_4

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    The dielectric constant and ac conductivity have been measured for the layered organic conductor theta-(BEDT-TTF)_2CsZn(SCN)_4 along the out-of-plane direction, which show a relaxation behavior similar to those in the charge-density-wave conductor. Most unexpectedly, they exhibit a large bias dependence with a hysteresis, and changes in magnitude by 100-1000 times at a threshold. These findings are very similar to the collective excitation of the charge density wave. theta-$(BEDT-TTF)_2CsZn(SCN)_4 has collective excitations associated with charge ordering, though it shows no clear indication of long range order.Comment: 8 pages, 6 figures, in RevTeX format, submitted to J. Phys. Soc. Jp
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