Entanglement of two delocalised electrons

Several convenient formulae for the entanglement of two indistinguishable delocalised spin-1/2 particles are introduced. This generalizes the standard formula for concurrence, valid only in the limit of localised or distinguishable particles. Several illustrative examples are given.Comment: 4 page

Non-adiabatically driven electron in quantum wire with spin-orbit interaction

An exact solution is derived for the wave function of an electron in a semiconductor quantum wire with spin-orbit interaction and driven by external time dependent harmonic confining potential. The formalism allows analytical expressions for various quantities to be derived, such as spin and pseudo-spin rotations, energy and occupation probabilities for excited states. It is demonstrated how perfect spin and pseudo-spin flips can be achieved at high frequencies of order \omega, the confining potential level spacing. By an appropriately chosen driving term, spin manipulation can be exactly performed far into the non-adiabatic regime. Implications for spin-polarised emission and spin-dependent transport are also discussed.Comment: 11 pages, 3 figure

General Green's function formalism for transport calculations with spd-Hamiltonians and giant magnetoresistance in Co and Ni based magnetic multilayers

A novel, general Green's function technique for elastic spin-dependent transport calculations is presented, which (i) scales linearly with system size and (ii) allows straightforward application to general tight-binding Hamiltonians (spd in the present work). The method is applied to studies of conductance and giant magnetoresistance (GMR) of magnetic multilayers in CPP (current perpendicular to planes) geometry in the limit of large coherence length. The magnetic materials considered are Co and Ni, with various non-magnetic materials from the 3d, 4d, and 5d transition metal series. Realistic tight-binding models for them have been constructed with the use of density functional calculations. We have identified three qualitatively different cases which depend on whether or not the bands (densities of states) of a non-magnetic metal (i) form an almost perfect match with one of spin sub-bands of the magnetic metal (as in Cu/Co spin valves); (ii) have almost pure sp character at the Fermi level (e.g. Ag); (iii) have almost pure d character at the Fermi energy (e.g. Pd, Pt). The key parameters which give rise to a large GMR ratio turn out to be (i) a strong spin polarization of the magnetic metal, (ii) a large energy offset between the conduction band of the non-magnetic metal and one of spin sub-bands of the magnetic metal, and (iii) strong interband scattering in one of spin sub-bands of a magnetic metal. The present results show that GMR oscillates with variation of the thickness of either non-magnetic or magnetic layers, as observed experimentally.Comment: 22 pages, 9 figure

Crystallization of the glassy phase of grain boundaries in silicon nitride

Three types of hot-pressed silicon nitride specimens (containing 5wt% Y2O3 and 2wt% Al2O3 additives) which were subjected to different temperature heat treatments were studied by X-ray diffraction, X-ray microanalysis and high resolution electron microscopy. The results indicated that there were phase changes in the grain boundaries after heat treatment and the glassy phase at the grain boundaries was crystallized by heat treatment

Spin detection at elevated temperatures using a driven double quantum dot

We consider a double quantum dot in the Pauli blockade regime interacting with a nearby single spin. We show that under microwave irradiation the average electron occupations of the dots exhibit resonances that are sensitive to the state of the nearby spin. The system thus acts as a spin meter for the nearby spin. We investigate the conditions for a non-demolition read-out of the spin and find that the meter works at temperatures comparable to the dot charging energy and sensitivity is mainly limited by the intradot spin relaxation.Comment: 8 pages, 6 figure

Entanglement between static and flying qubits in a semiconducting carbon nanotube

Entanglement can be generated by two electrons in a spin-zero state on a semiconducting single-walled carbon nanotube. The two electrons, one weakly bound in a shallow well in the conduction band, and the other injected into the conduction band, are coupled by the Coulomb interaction. Both transmission and entanglement are dependent on the well characteristics, which can be controlled by a local gate, and on the kinetic energy of the injected electron. Regimes with different degrees of electron correlation exhibit full or partial entanglement. In the latter case, the maximum entanglement can be estimated as a function of width and separation of a pair of singlet-triplet resonances.Comment: 17 pages and 12 figures, accepted to J. Phys. Cond. Ma