Transport signatures of an Andreev molecule in a quantum dot -- superconductor -- quantum dot setup

TL;DR

This paper provides a theoretical analysis of a quantum dot-superconductor-quantum dot device, identifying how different non-local mechanisms influence measurable properties, aiding experimental characterization and optimization for quantum information applications.

Contribution

It systematically studies the effects of dominant non-local mechanisms in a Cooper-pair splitter, offering clear experimental signatures for their identification.

Findings

Distinct signatures for crossed Andreev reflection, elastic cotunneling, and direct interdot tunneling.

Analysis of triplet blockade and negative differential conductance phenomena.

Guidelines for experimental characterization and device optimization.

Abstract

Hybrid devices combining quantum dots with superconductors are important building blocks of conventional and topological quantum-information experiments. A requirement for the success of such experiments is to understand the various tunneling-induced non-local interaction mechanisms, namely, crossed Andreev reflection, elastic cotunneling, and direct interdot tunneling, that are present in the device. Here, we provide a theoretical study of a simple device which consists of two quantum dots and a superconductor tunnel-coupled to the dots, often called a Cooper-pair splitter. We study the three special cases where one of the three non-local mechanisms dominates, and calculate measurable ground-state properties, as well as the zero-bias and finite-bias differential conductance characterizing electron transport through this device. We describe how each non-local mechanism controls the measurable quantities, and thereby find experimental fingerprints that allow one to identify and quantify the dominant non-local mechanism using experimental data. Finally, we study the triplet blockade effect and the associated negative differential conductance in the Cooper-pair splitter, and show that they can arise regardless of the nature of the dominant non-local coupling mechanism. Our results should facilitate the characterization of hybrid devices, and their optimization for various quantum-information-related experiments and applications.