Non local quantum state engineering with the Cooper pair splitter beyond the Coulomb blockade regime

TL;DR

This paper explores a new regime for Cooper pair splitters where the charging energy is less than the superconducting gap, enabling the engineering of spin triplet states and enhancing non-local entanglement of electron pairs.

Contribution

It introduces a theoretical analysis of Cooper pair splitters beyond the Coulomb blockade, showing how to generate spin triplet states via superconductor-mediated inter-dot tunneling.

Findings

Superconductor mediates an inter-dot tunneling with spin symmetry influenced by Zeeman field.

Engineered quantum dots can produce entangled non-local electron pairs.

Extended the operational regime of Cooper pair splitters beyond traditional Coulomb blockade limits.

Abstract

A Cooper pair splitter consists of two quantum dots side-coupled to a conventional superconductor. Usually, the quantum dots are assumed to have a large charging energy compared to the superconducting gap, in order to suppress processes other than the coherent splitting of Cooper pairs. In this work, in contrast, we investigate the limit in which the charging energy is smaller than the superconducting gap. This allows us, in particular, to study the effect of a Zeeman field comparable to the charging energy. We find analytically that in this parameter regime the superconductor mediates an inter-dot tunneling term with a spin symmetry determined by the Zeeman field. Together with electrostatically tunable quantum dots, we show that this makes it possible to engineer a spin triplet state shared between the quantum dots. Compared to previous works, we thus extend the capabilities of the Cooper pair splitter to create entangled non local electron pairs.