Non-local Andreev Reflection as a Source of Entangled Electrons

Cooper pairs in conventional superconductors form a robust reservoir of spin-entangled singlet ``particles''. This has led to many theoretical proposals for the realization of ``entangler'' devices --i.e. devices capable of sourcing currents carried by entangled pairs into nanoelectronic circuits- that are of fundamental interest in the field of quantum information. These proposals rely on the possibility to ``split'' Cooper pairs by injecting the two constituent electrons into two spatially separated normal metal leads attached to a superconductors. It has been shown theoretically that such a Cooper-pair ``splitting'' process is equivalent to the process of non-local Andreev reflection, in which an electron (hole) injected from a metallic electrode connected to a superconductor is transmitted into a hole (electron) into a second, spatially separated electrode. In this talk I will discuss recent experiments[1] performed in Delft that demonstrate the occurrence of non-local Andreev reflection as a quantum mechanically phase coherent process. [1] S. Russo \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 027002 (2005)