Showing papers by "Saburo Takahashi published in 2006"

Superconducting π qubit with three Josephson junctions

Abstract: We propose a qubit consisting of a superconducting ring with two zero junctions and one ferromagnetic π junction. In the system, degenerate states appear in the phase space without an external magnetic field because of a competition between the zero and π states. Quantum tunneling between the degenerate states leads to a formation of bonding and antibonding states which are used as a bit. For manipulating the states, only a small magnetic field around zero is required. This feature leads to a large-scale integration and a construction of the smaller-sized qubit which is robust to the decoherence by external noises.

Spin injection and transport in magnetic nanostructures

Abstract: We theoretically study the spin transport in a device consisting of a nonmagnetic metal (N) connected to ferromagnetic injector (F1) and detector (F2) electrodes. We solve the spin-dependent transport equations in a device with arbitrary interface resistance from a metallic-contact to tunneling regime, and obtain the conditions for efficient spin injection, accumulation, and transport in the device. In a spin-injection device containing a superconductor (F1/S/F2), we examine the effect of superconductivity on the spin transport. The spin-current induces the anomalous Hall effect in nonmagnetic conductors is also discussed.

Controllable π junction with magnetic nanostructures

Abstract: We propose a novel Josephson device in which 0 and $\pi$ states are controlled by an electrical current. In this system, the $\pi$ state appears in a superconductor/normal metal/superconductor junction due to the non-local spin accumulation in the normal metal which is induced by spin injection from a ferromagnetic electrode. Our proposal offers not only new possibilities for application of superconducting spin-electronic devices but also the in-depth understanding of the spin-dependent phenomena in magnetic nanostructures.

Magnetic impurity states and ferromagnetic interaction in diluted magnetic semiconductors

Abstract: The electronic structure of diluted magnetic semiconductors is studied, especially focusing on the hole character. The Haldane-Anderson model is extend to a magnetic impurity, and is analyzed in the Hartree-Fock approximation. Due to the strong hybridization of an impurity d-states with host p-states, it is shown that holes are created in the valence band, at the same time the localized magnetic moments are formed. These holes are weakly bound around the impurity site with the characteristic length of several lattice constants. For the case of the two impurities, it is found that when the separation of two impurities is of the order of the length of holes, the overlap of these holes favors the ferromagnetic interaction. The spatially extended holes play an essential role for the ferromagnetic exchange interaction.

Database device, database construction method, and data search method

Abstract: PROBLEM TO BE SOLVED: To provide a database device performing search at high speed without requiring a heavy load for creation and maintenance. SOLUTION: On at least one side of a map table 20 constructing a relation structure of this database device, a root table 21 and a plurality of branch tables 22-25 are arranged. The respective branch tables include data of the same kind of item. The root table 21 can individually specify multiple items covered by a plurality of branch tables 22-25. The respective data in the branch tables 22-24 are associated with the root table 21 in one-to-one correspondence. By the map table 20, the root table 21 is associated in many-to-many correspondence with a table 26 on the opposite side. One map table and a plurality of tables for the respective item types can coexist. Desirably, a reference amount of the root table 21 and that of the branch tables 22-25 are compared mutually based on a search condition, and a search sequence is decided. COPYRIGHT: (C)2007,JPO&INPIT