Microwave-frequency scanning gate microscopy of a Si/SiGe double quantum dot

TL;DR

This paper introduces a microwave-frequency scanning gate microscopy technique for Si/SiGe double quantum dots, combining spatial resolution with microwave energy sensitivity to study quantum states and valley splittings.

Contribution

It demonstrates the use of a scanning probe with microwave excitation to resolve energy levels and photon-assisted tunneling in quantum dots, enhancing spatial and energy resolution.

Findings

Resolved ~65 μeV excited states in the double dot

Demonstrated charge occupancy control with a dc-biased tip

Measured photon-assisted tunneling resonance conditions

Abstract

Conventional quantum transport methods can provide quantitative information on spin, orbital, and valley states in quantum dots, but often lack spatial resolution. Scanning tunneling microscopy, on the other hand, provides exquisite spatial resolution of the local electronic density of states, but often at the expense of speed. Working to combine the spatial resolution and energy sensitivity of scanning probe microscopy with the speed of microwave measurements, we couple a metallic probe tip to a Si/SiGe double quantum dot that is integrated with a local charge detector. We first demonstrate that a dc-biased tip can be used to change the charge occupancy of the double dot. We then apply microwave excitation through the scanning tip to drive photon-assisted tunneling transitions in the double dot. We infer the double dot energy level diagram from the frequency and detuning dependence of the photon-assisted tunneling resonance condition. These measurements allow us to resolve $\sim$65 $\mu$eV excited states, an energy scale consistent with typical valley splittings in Si/SiGe. Future extensions of this approach may allow spatial mapping of the valley splitting in Si devices, which is of fundamental importance for spin-based quantum processors.