A reliable source of entangled states for use in quantum computing is highly sought after. One such source option is the Cooper pairs in a BCS superconductor. By fabricating a Cooper pair splitter using a central superconducting lead coupled to two quantum dots the hope is that the Cooper pairs can be split and continued entanglement measured. This master thesis describes the fabrication steps and complications of fabricating a Cooper pair splitter using Vanadium as the central superconducting lead. Fabrication of the precise Cooper pair splitter geometry was successfully achieved. Unforeseen obstacles in a series resistance occurring in the normal contacts convoluted the data set however. The superconducting properties of the Vanadium was difficult to observe as well. This was believed to be a consequence of impurities mixing with the Vanadium during the fabrication process. A correction for the series resistance in the normal contacts was achieved and characterization of the nanotubes showed promising results of features needed for entanglement detection. It is also believed that a change in the fabrication process of the Vanadium superconductor is possible. Cooper pair splitters using Vanadium is thus still of interest.
Spin-orbit interaction provides a spin filtering effect in carbon nanotube based Cooper pair splitters that allows us to determine spin correlators directly from current measurements. The spin filtering axes are tunable by a global external magnetic field. By a bending of the nanotube, the filtering axes on both sides of the Cooper pair splitter become sufficiently different that a test of entanglement of the injected Cooper pairs through a Bell-like inequality can be implemented. This implementation does not require noise measurements, supports imperfect splitting efficiency and disorder, and does not demand a full knowledge of the spin-orbit strength. Using a microscopic calculation we demonstrate that entanglement detection by violation of the Bell-like inequality is within the reach of current experimental setups.