Entanglement plays a central role in the emerging quantum technology. With original experiments the nanoelectronics group at the University of Basel (www.nanoelectronics.ch) created a new source of spin-entangled electron pairs based on a superconductor. In this device, known as the Cooper-pair splitter (CPS), the two electrons of a Cooper-pair are made to tunnel into two different quantum dots (QDs). The splitting is induced by Coulomb interaction through the QDs. Though we could demonstrate a remarkably high splitting efficiency of > 90%, there are many device parameters that are barely controlled and understood. For example, we currently cannot control all tunneling couplings. Furthermore, there are open questions with regard to the proximity effect, the role of spin-orbit interaction and valley splitting, and additionally, no entanglement test could be realized until today.

This proposal addresses these questions using three different material system: semiconducting nanowires (NWs), carbon nanotubes (CNTs) and graphene. These low dimensional systems have attracted a growing interest in recent years due to the unique properties of charge and spin which stem from strong spin-orbit interaction in NWs and chiral, neutrino-like properties of the quasiparticles in grapheme and CNTs. The combination of high-quality low-dimensional materials with nanostructured superconducting and ferromagnetic materials in so-called hybrid devices not only allows the realization and study of CPS, but also provides versatile experimental platforms for the exploration of a wide range of novel physical phenomena, including unconventional superconductivity, proximity-induced electron correlations and Majorana fermions. Specifically, we will work on improved tunable CPS devices, entanglement measurements using non-collinear magnetic fields, proximity-induced coupling between the two QDs, where so-called “poor-man’s” Majorana states can emerge.