Double quantum dot Cooper-pair splitter at finite couplings

TL;DR

This paper analyzes the transport and entanglement properties of a double quantum dot Cooper-pair splitter, revealing how Coulomb interactions, tunneling, and spin-orbit coupling influence nonlocal entanglement and current symmetry.

Contribution

It provides an exact treatment of dot-superconductor coupling and explores how Coulomb interactions and spin-orbit effects control nonlocal entanglement in the device.

Findings

Inter-dot tunneling affects particle-hole symmetry of currents.

Spin-orbit interaction enables control over nonlocal entanglement.

Nonlocal entanglement can be generated without direct nonlocal coupling.

Abstract

We consider the sub-gap physics of a hybrid double-quantum dot Cooper-pair splitter with large single-level spacings, in the presence of tunnelling between the dots and finite Coulomb intra- and inter-dot Coulomb repulsion. In the limit of a large superconducting gap, we treat the coupling of the dots to the superconductor exactly. We employ a generalized master-equation method which easily yields currents, noise and cross-correlators. In particular, for finite inter- and intra-dot Coulomb interaction, we investigate how the transport properties are determined by the interplay between local and nonlocal tunneling processes between the superconductor and the dots. We examine the effect of inter-dot tunneling on the particle-hole symmetry of the currents with and without spin-orbit interaction. We show that spin-orbit interaction in combination with finite Coulomb energy opens the possibility to control the nonlocal entanglement and its symmetry (singlet/triplet). We demonstrate that the generation of nonlocal entanglement can be achieved even without any direct nonlocal coupling to the superconducting lead.