Directly visualizing the energy level structure of quantum dot molecules

TL;DR

This paper presents a spectroscopy method to map the energy level structure of silicon quantum dot molecules, revealing atom-like and molecular-like states, valley splitting, and singlet-triplet splitting.

Contribution

It introduces a spectroscopy technique capable of directly visualizing the energy spectrum of double quantum dots across various parameters.

Findings

Transition from atom-like to molecular-like energy levels observed.

Zeeman splitting of valley states resolved in magnetic field.

Detuning-dependent singlet-triplet splitting measured.

Abstract

The orbital, spin and valley degrees of freedom in silicon quantum dots support many modes of spin qubit operation. However, it is generally challenging to obtain information about the energy level spectrum over large ranges of parameter space. We demonstrate a form of spectroscopy that is capable of mapping the energy level structure of a double quantum dot as a function of level detuning, interdot tunnel coupling, and magnetic field. In the one electron regime, we directly observe the transition from the atom like energy levels of isolated quantum dots to molecular like bonding and anti bonding states with increasing interdot tunnel coupling. We also resolve the Zeeman splitting of ground and excited valley states in a magnetic field. In the two electron regime, we gain access to the detuning dependent singlet triplet splitting. Our work may be extended to a broader class of systems, such as strong spin-orbit materials or proximitized quantum dots, allowing the direct extraction of various energy gaps.