Spectroscopy and level detuning of few-electron spin states in parallel InAs quantum dots

TL;DR

This study uses tunneling spectroscopy to explore spin states in parallel InAs nanowire double quantum dots, revealing detailed excited state transport behavior and spin-orbit effects relevant for quantum computing applications.

Contribution

It provides new insights into spin state evolution in parallel quantum dots and demonstrates the ability to resolve triplet states and their hybridization with singlets under magnetic fields.

Findings

Resolved all triplet states near avoided crossings.

Observed symmetry between electron transitions due to spin degeneracy.

Successfully modeled experimental data with a simple orbital model.

Abstract

We use tunneling spectroscopy to study the evolution of few-electron spin states in parallel InAs nanowire double quantum dots (QDs) as a function of level detuning and applied magnetic field. Compared to the much more studied serial configuration, parallel coupling of the QDs to source and drain greatly expands the probing range of excited state transport. Owing to a strong confinement, we can here isolate transport involving only the very first interacting single QD orbital pair. For the (2,0)-(1,1) charge transition, with relevance for spin-based qubits, we investigate the excited (1,1) triplet, and hybridization of the (2,0) and (1,1) singlets. An applied magnetic field splits the (1,1) triplet, and due to spin-orbit induced mixing with the (2,0) singlet, we clearly resolve transport through all triplet states near the avoided singlet-triplet crossings. Transport calculations, based on a simple model with one orbital on each QD, fully replicate the experimental data. Finally, we observe an expected mirrored symmetry between the 1-2 and 2-3 electron transitions resulting from the two-fold spin degeneracy of the orbitals.