Density of States (Gate) - Controlled Andreev Molecule and Sensor

TL;DR

This paper presents a gate-controlled Andreev molecule platform that enhances tunability and scalability in topological quantum devices, enabling noninvasive charge sensing and advancing toward topological qubits.

Contribution

It introduces a novel gate-controlled Andreev molecule that removes the need for magnetic flux, improving control and scalability in topological quantum systems.

Findings

Gate control nonlocally enhances critical current

Eliminates superconducting loops for better tunability

Enables single-Cooper-pair charge sensing

Abstract

Topological quantum computing typically relies on topological Andreev bound states (ABSs) engineered in hybrid superconductor-semiconductor devices, where gate control offers key advantages. While strong Zeeman fields can induce such states, an alternative approach emerges through Andreev molecules -- closely spaced, coupled ABSs, also key building-block for Kitaev chain -- that enable topological behavior without high magnetic fields. However, existing Andreev molecules are controlled via magnetic flux in superconducting loops, limiting scalability. Here, we introduce a gate-controlled Andreev molecule, where electrostatic tuning of the density of states in one site nonlocally enhances the critical current of another. This eliminates superconducting loops, offering superior tunability, scalability, and sensitivity. We further extend such an Andreev molecule to a multi-site Kitaev chain, and a noninvasive sensor resolving single-Cooper-pair charge for parity readout. This platform bridges the gap between scalable ABS engineering and high-sensitivity quantum sensing, advancing the development for constructing and parity-readout in topological ABSs and long Kitaev chains towards topological qubits.