Master theses defense by Kathrine Bjørn Knudson

Simulating operations of mobile hole spins in Germanium

Quantum mechanical spins confined in semiconductor structures exhibit spin-orbit coupling properties of great interest for their potential technological applications. However, achieving precise control over these properties is often limited by an incomplete understanding of the semiconductor environment. Simulations play a crucial role in guiding experimental efforts, by providing information on key device parameters and identifying optimal regimes of operation. In this thesis, we present a numerical simulation framework of planar semiconductor devices hosting gate-confined double quantum dots. The framework is based on open-source software, and provides features for numerical estimations of various metrics, along with a range of visualization tools. We show numerically a dependence of the spin-orbit coupling on the voltage applied on the plunger gates, across difference device configurations. However, the magnitude of spin-orbit couplings presented here, are not opportune for performing spin-orbit based operations, as they are quite small. We attribute this to the limited types of device configurations investigated, and an extended analysis of the model parameters and their influence on the magnitude of spin-orbit coupling, is necessary to provide further insights into how to enhance these effects. As a use case of the simulated data, we demonstrate a numerical time simulation of a hopping protocol, using tunneling accompanied by spin rotation for implementation of single-spin manipulation. We estimate fidelities and corresponding appropriate optimal gate operation times, along with estimates of the charge noise impact on the protocol due to different state transitions. Due to the low spin-orbit coupling predicted from the simulated data, the protocols performed are predicted to be inefficient.

This thesis provides a numerical approach to gaining insights into the behavior of the semiconductor environments, supplementing previous theoretical work on spin-orbit based qubit operations.