Corey Ostrove, UT-Austin

"Noise Cross-Correlations and Entanglement in Superconducting Heterostructures"

Abstract: In recent years there has been a resurgence of interest in the nonlocal transport properties of superconducting heterostructures due to the possibility of their serving as a source of electronic entanglement in solid state quantum information processors. Devices designed for this purpose are called Cooper pair splitting devices. The utility of these devices as entanglement sources is known to have connections to the positivity of noise cross correlations in spatially separated leads.

Previous studies have focused primarily on devices with some variation of an NSN-type (normal-superconducting-normal) geometry. In this talk I'll be discussing our work extending this analysis using the framework of Bogoliubov-de Gennes scattering theory (without the Andreev approximation) to the more complicated NSNSN geometry. An important new feature introduced in this setting is the existence of long-lived sub-gap quasibound states. We find that these quasibound states produce strong resonances at energies below the superconducting gap energy and strongly influence the energy distributions of the cross-correlated shot noise. We compare the results of the exact scattering theory with those using the Andreev approximation and find that the Andreev approximation breaks down in the vicinity of the quasibound states.