# Effects of Interface Steps on the Valley Orbit coupling in a Si/SiGe quantum dot

## TL;DR

This study investigates how interface steps influence the magnitude and phase of valley-orbit coupling in silicon quantum dots, revealing significant suppression and phase shifts caused by atomic-scale interface roughness, with implications for silicon-based quantum computing.

## Contribution

It provides a detailed analysis of the impact of interface steps on valley-orbit coupling in Si/SiGe quantum dots, highlighting the importance of interface roughness in qubit performance.

## Key findings

- Valley-orbit coupling magnitude can be suppressed by up to 75% by a single atomic step.
- The phase of valley-orbit coupling can change by nearly π due to interface steps.
- Presence of two steps can reduce valley-orbit coupling close to zero.

## Abstract

Valley-orbit coupling is a key parameter for a silicon quantum dot in determining its suitability for applications in quantum information processing. In this paper we study the effect of interface steps on the magnitude and phase of valley-orbit coupling for an electron in a silicon quantum dot. Within the effective mass approximation, we find that the location of a step on the interface is important in determining both the magnitude and the phase of the valley-orbit coupling in a Si/SiGe quantum dot. Specifically, our numerical results show that the magnitude of valley orbit coupling can be suppressed up to 75\% by a step of one atomic monolayer, and its phase can change by almost $\pi$. When two steps are present, the minimum value of the valley-orbit coupling can even approach zero. We also clarify the effects of an applied external magnetic field and the higher orbital states on the valley-orbit coupling. Overall, our results illustrate how interface roughness affect the valley-orbit coupling in silicon, and how spin qubits in silicon may be affected.