Master's Defense: Morten Hels – University of Copenhagen

Master's Defense: Morten Hels

Toward entanglement detection
Non-collinear spin-orbit magnetic fields in a bent carbon nanotube

Abstract: In a Cooper pair splitter device Cooper pairs are made to split into two parallel quantum dots connected to a superconductor. Previous experiments have shown that such devices can show non-local charge correlations indicating that Cooper pairs are, indeed, responsible for the transport. What remains to be seen is that the Cooper pairs are actually entangled when they split. Recently Braunecker et al. (PRL 111, 136806 (2013)) have made a proposal for realizing entanglement detection.

This master thesis presents low-temperature measurements of a carbon nanotube Cooper pair splitter device. The device is shown to satisfy almost all the requirements of the above proposal. Specifically, the spin-orbit magnetic fields in the device are shown to be non-collinear and spin-orbit coupling dominates disorder in one of the nanotube segments. A non-local current signal is also measured in the device, but due to Kondo resonances analyzing it is not straightforward. These results are promising for the entanglement detection scheme above and for other proposals involving spin-filtering.