Sydney, Australia, 26 June 2023 – Atom-based qubits in silicon represent the most precise platform in the solid state for scalable quantum processors. Core to understanding the operation of single and two qubit gates in these processors is to observe the underlying qubit wave functions and how these are controlled by metallic gates during device operation.

In this work the atomic-scale spatial resolution of the scanning tunnelling microscope is used to directly access, and map out, the wave functions of electrons on precision placed phosphorus atoms in silicon under controlled voltage conditions. Such exquisite control of how the electron wavefunction behaves during device conditions provides direct information into how to optimise designs for high fidelity operation.

Importantly, SQC has now merged three different atomic-scale assets simultaneously: the ability to precision place phosphorus atoms in silicon to form circuit elements such as qubits and gates whilst now being able to image the wavefunction directly under device control. By combining ion implantation with STM lithography on an insulating substrate, using light to maintain STM stability, the team were able to bring together local scanning tunnelling spectroscopy with in-plane gate control of precision placed atoms for local gating.

Such a globally unique technique allows us for the first time to demonstrate in-situ control of the relative energy levels within the device using a local gate under different operating conditions. Such a breakthrough creates a distinctive solid-state quantum microscope to map qubit wavefunctions, enabling us to realise optimal device designs as we create programmable quantum processors.

Read the full paper here – A solid-state quantum microscope for wavefunction control of an atom-based quantum dot device in silicon in Nature Electronics.

Authors: B. Voisin, J. Salfi, D. D. St Médar, B. C. Johnson, J. C. McCallum, M. Y. Simmons & S. Rogge.