We investigate quantum teleportation through noisy quantum channels by solving analytically and numerically a master equation in the Lindblad form. We calculate the fidelity as a function of decoherence rates and angles of a state to be teleported. It is found that the average fidelity and the range of states to be accurately teleported depend on types of noises acting on quantum channels. If the quantum channels are subject to isotropic noise, the average fidelity decays to 1/2, which is smaller than the best possible value of 2/3 obtained only by the classical communication. On the other hand, if the noisy quantum channel is modeled by a single Lindblad operator, the average fidelity is always greater than 2/3. Quantum teleportation ͓1,2͔ is a process by which a sender, called Alice, transmits an unknown quantum state to a remote recipient, called Bob, via dual classical and quantum channels. Here a pair of maximally entangled particles, forming a quantum channel, should be used for the perfect quantum teleportation. However, while being distributed and kept by Alice and Bob, an entangled state may lose its coherence and become a mixed state due to the interaction with its environment.Bennett et al. ͓1͔ noted that the quantum channel that is less entangled reduces the fidelity of teleportation, and/or the range of states that can be accurately teleported. Popescu ͓3͔ investigated the relations among teleportation, Bell's inequalities, and nonlocality. It was demonstrated that there are mixed states that do not violate any Bell-type inequality, but still can be used for teleportation. Horodecki et al. ͓4͔ showed that any two mixed spin-1 2 states that violate the Bell-CHSH inequality are useful for teleportation. Also Horodecki et al. ͓6͔ proved the relation between the optimal fidelity of teleportation and the maximal singlet fraction of the quantum channel. Banaszek ͓7͔ investigated the fidelity of quantum teleportation using nonmaximally entangled states. Ishizaka ͓8͔ studied the quantum channel subject to local interaction with two-level environment. Although the studies cited above reveal the important relations between the degree of entanglement of the quantum channel and quantum teleportation, there seem to be little studies on the direct connection between the quantum teleportation and decoherence rates. Thus it might be interesting to know how the type and strength of noise acting on quantum channels affect the fidelity of quantum teleportation.In this paper, we investigate quantum teleportation through noisy channels by solving analytically and numerically a master equation in the Lindblad form. We obtain the fidelity of quantum teleportation as a function of decoherence time and angles of an unknown state to be teleported. Thus we explicitly demonstrate Bennett et al.'s argument that noisy quantum channels reduce the range of states to be accurately teleported. We also examine the characteristic dependence of the average fidelity on types of noises acting on qubits at each stage of the teleportatio...

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Fe- and Cu-codoped ZnO was previously reported as a room-temperature dilute magnetic semiconductor. We have investigated the origin of the ferromagnetism in Zn0.95−xFe0.05CuxO using the zero-field Fe57 nuclear magnetic resonance and neutron diffraction. These measurements reveal that some Fe ions of Zn0.95−xFe0.05CuxO form a secondary phase, ZnFe2O4. Detailed comparison of nuclear magnetic resonance spectra of Zn0.95−xFe0.05CuxO, bulk ZnFe2O4 with normal spinel structure, and nanocrystalline ZnFe2O4 with inverted spinel structure shows that the secondary phase possesses an inverted spinel structure and is ferrimagnetic at room temperature, while normal zinc ferrite is nonmagnetic. The ferromagnetism in Fe- and Cu-codoped ZnO stems from the secondary phase, while the majority of Fe ions substituted into the ZnO lattice appears to remain magnetically inert.

In this research, we investigated the migration of particles in the tube flow of suspension for a wide range of particle loading (φ0) and particle Reynolds number (Rep), using a magnetic resonance imaging (MRI) technique. The suspension consisted of nearly monodisperse polymethylmethacrylate spheres in a density matched Newtonian fluid. The volume fraction of the solid was 0.06–0.40. Both the velocity and the concentration distributions were measured under fully developed conditions. It has been found that, when φ0 was small (⩽0.1) and Rep was not small (>≈0.2), the particles moved toward the position at a distance of 0.5–0.6 R (tube radius) from the tube axis and the velocity profile was parabolic. When φ0=0.4, particles always moved toward the center of the tube and the velocity profile was blunted. The degree of blunting was larger for smaller Rep. Between these two limiting cases, the particle migration was dependent on Rep. When Rep is small the particles move toward the tube axis regardless of φ0. When φ0 is 0.2–0.3 and Rep>≈0.2, particles are concentrated both at the center and at the middle of the tube axis and tube wall. The velocity profile keeps the parabolic form unless the particles are concentrated regardless of Rep. Apparent wall slip is not observed except for the case of φ0=0.40. It is suggested that, when the particle Reynolds number is larger than 0.1, the inertial effect cannot be neglected regardless of the average particle concentration.