Impact of the valley orbit coupling on exchange gate for spin qubits in silicon quantum dots

TL;DR

This paper investigates how valley phase differences in silicon quantum dots influence exchange interactions, revealing suppression effects critical for spin qubit gate performance.

Contribution

It provides a detailed analysis of valley phase effects on exchange splitting using configuration interaction calculations, highlighting the role of higher orbital states.

Findings

Exchange splitting is suppressed at a valley phase difference of π.

Higher orbital states significantly influence exchange energy.

Valley-phase-dependent dressing affects singlet and triplet states.

Abstract

The presence of degenerate conduction band valleys and how they are mixed by interfaces play critical roles in determining electron interaction and spectrum in a silicon nanostructure. Here we investigate how the valley phases affect the exchange interaction in a symmetric two-electron silicon double quantum dot. Through a configuration interaction calculation, we find that exchange splitting is suppressed at a finite value of valley phase difference between the two dots, and reaches its minimum value ({\sim} 0) when the phase difference is {\pi}. Such a suppression can be explained using the Hubbard model, through the valley-phase-dependent dressing by the doubly occupied states on the ground singlet and triplet states. The contributions of the higher orbital states also play a vital role in determining the value of the exchange energy in general, which is a crucial parameter for applications such as exchange gates for spin qubits.