State-conditional coherent charge qubit oscillations in a Si/SiGe quadruple quantum dot

TL;DR

This paper demonstrates state-conditional coherent oscillations in a Si/SiGe quadruple quantum dot, showcasing fast two-qubit control and strong capacitive coupling, advancing the development of scalable quantum computing architectures.

Contribution

First demonstration of coherent two-axis control of a charge qubit in undoped Si/SiGe quadruple quantum dots with measured strong capacitive coupling.

Findings

Measured detuning energy shift of ~75 μeV due to capacitive coupling.

Achieved conditional π phase flip in about 80 ps.

Demonstrated fast conditional Landau-Zener-Stückelberg interference.

Abstract

Universal quantum computation requires high fidelity single qubit rotations and controlled two qubit gates. Along with high fidelity single qubit gates, strong efforts have been made in developing robust two qubit logic gates in electrically-gated quantum dot systems to realize a compact and nano-fabrication-compatible architecture. Here, we perform measurements of state-conditional coherent oscillations of a charge qubit. Using a quadruple quantum dot formed in a Si/SiGe heterostructure, we show the first demonstration of coherent two-axis control of a double quantum dot charge qubit in undoped Si/SiGe, performing Larmor and Ramsey oscillation measurements. We extract the strength of the capacitive coupling between double quantum dots by measuring the detuning energy shift ($\approx$ 75 $\mu$eV) of one double dot depending on the excess charge configuration of the other double dot. We further demonstrate that the strong capacitive coupling allows fast conditional Landau-Zener-Stuckelberg interferences with conditonal $\pi$ phase flip time about 80 ps, showing promising pathways toward multi-qubit entanglement control in semiconductor quantum dots.