A low-disorder Metal-Oxide-Silicon double quantum dot

TL;DR

This paper reports the development of a low-disorder MOS quantum double-dot device with low critical electron densities, enabling single-electron control and demonstrating potential for scalable MOS-based spin qubits.

Contribution

The work introduces a low-disorder MOS quantum dot device with near-ideal critical densities, enabling single-electron regime operation and detailed characterization of charge traps and valley splitting.

Findings

Achieved critical electron densities comparable to high-quality Si/SiGe devices

Measured charging energies around 8 meV consistent with dot size

Detected three electron traps and characterized charge noise and valley splitting

Abstract

One of the biggest challenges impeding the progress of Metal-Oxide-Silicon (MOS) quantum dot devices is the presence of disorder at the Si/SiO$_2$ interface which interferes with controllably confining single and few electrons. In this work we have engineered a low-disorder MOS quantum double-dot device with critical electron densities, i.e. the lowest electron density required to support a conducting pathway, approaching critical electron densities reported in high quality Si/SiGe devices and commensurate with the lowest critical densities reported in any MOS device. Utilizing a nearby charge sensor, we show that the device can be tuned to the single-electron regime where charging energies of $\approx$8 meV are measured in both dots, consistent with the lithographic size of the dot. Probing a wide voltage range with our quantum dots and charge sensor, we detect three distinct electron traps, corresponding to a defect density consistent with the ensemble measured critical density. Low frequency charge noise measurements at 300 mK indicate a 1/$f$ noise spectrum of 3.4 $\mu$eV/Hz$^{1/2}$ at 1 Hz and magnetospectroscopy measurements yield a valley splitting of 110$\pm$26 $\mu$eV. This work demonstrates that reproducible MOS spin qubits are feasible and represents a platform for scaling to larger qubit systems in MOS.