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