Current and Shot Noise Measurements in a Carbon Nanotube-Based Spin Diode

Low-temperature measurements of asymmetric carbon nanotube (CNT) quantum dots are reported. The CNTs are end-contacted with one ferromagnetic and one normal-metal electrode. The measurements show a spin-dependent rectification of the current caused by the asymmetry of the device. This rectification occurs for gate voltages for which the normal-metal lead is resonant with a level of the quantum dot. At the gate voltages at which the current is at the maximum current, a significant decrease in the current shot noise is observed

Coulomb scattering cross-section in a 2D electron gas and production of entangled electrons

We calculate the Coulomb scattering amplitude for two electrons injected with opposite momenta in an interacting 2DEG. We include the effect of the Fermi liquid background by solving the 2D Bethe-Salpeter equation for the two-particle Green function vertex, in the ladder and random phase approximations. This result is used to discuss the feasibility of producing spin EPR pairs in a 2DEG by collecting electrons emerging from collisions at a pi/2 scattering angle, where only the entangled spin-singlets avoid the destructive interference resulting from quantum indistinguishability. Furthermore, we study the effective 2D electron-electron interaction due to the exchange of virtual acoustic and optical phonons, and compare it to the Coulomb interaction. Finally, we show that the 2D Kohn-Luttinger pairing instability for the scattering electrons is negligible in a GaAs 2DEG.Comment: 19 pages, 10 figure

Semiclassical description of resonant tunneling

We derive a semiclassical formula for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The calculations idealize an experimental situation where a strong magnetic field tilted with respect to an electric field is used. The resulting semiclassical expression is written as the sum over special periodic orbits which hit both walls of the quantum well and are perpendicular to the first wall.Comment: LaTeX, 8 page

Fermi liquid parameters in 2D with spin-orbit interaction

We derive analytical expressions for the quasiparticle lifetime tau, the effective mass m*, and the Green's function renormalization factor Z for a 2D Fermi liquid with electron-electron interaction in the presence of the Rashba spin-orbit interaction. We find that the modifications are independent of the Rashba band index rho, and occur in second order of the spin-orbit coupling alpha. In the derivation of these results, we also discuss the screening of the Coulomb interaction, as well as the susceptibility and the self-energy in small alpha.Comment: 9 pages, 1 fig. Corrected the result for the effective mass, and added a section IV.B. Corrected typos and updated reference

Highly Entangled Ground States in Tripartite Qubit Systems

We investigate the creation of highly entangled ground states in a system of three exchange-coupled qubits arranged in a ring geometry. Suitable magnetic field configurations yielding approximate GHZ and exact W ground states are identified. The entanglement in the system is studied at finite temperature in terms of the mixed-state tangle tau. By adapting a steepest-descent optimization algorithm we demonstrate that tau can be evaluated efficiently and with high precision. We identify the parameter regime for which the equilibrium entanglement of the tripartite system reaches its maximum.Comment: 4 pages, 2 figure

Toy models of crossed Andreev reflection

We propose toy models of crossed Andreev reflection in multiterminal hybrid structures containing out-of-equilibrium conductors. We apply the description to two possible experiments: (i) to a device containing a large quantum dot inserted in a crossed Andreev reflection circuit. (ii) To a device containing an Aharonov-Bohm loop inserted in a crossed Andreev reflection circuit.Comment: 5 pages, 9 figures, minor modification