arXiv subjects

Arthur Lin

Publications and source records attributed to Arthur Lin.

3 recordsLinked to original sources

arXiv2026

Anisotropy reduction and tunability of hole-spin qubit g-factor in strained parabolic Ge/SiGe quantum wells

Hole-spin qubits in planar Ge/SiGe heterostructures have attracted significant attention in recent years owing to their favorable electrical characteristics and prolonged coherence times. However, the strong spin-orbit interaction also makes them susceptible to charge noise and inhomogeneous strain. This is further exacerbated by the highly anisotropic g-factor of the planar design. Although there are some known strategies to suppress charge noise, one approach is to engineer an isotropic g-factor. In this work we analyze how qubit confinement profile affects the g-factor of hole-spin qubits. We show that decreasing the characteristic in-plane qubit confinement length reduces the g-factor anisotropy. We perform analytical and numerical analysis to compare two types of quantum wells: square wells and parabolic wells. We show that square wells have limited tunability, while parabolic wells offer broader tunability, making them more promising for qubit engineering.

cond-mat.mes-hall↗

arXiv2023

Incorporation of random alloy GaBi$_{x}$As$_{1-x}$ barriers in InAs quantum dot molecules: alloy strain and orbital effects towards enhanced tunneling

Self-assembled InAs quantum dots (QDs), which have long hole-spin coherence times and are amenable to optical control schemes, have long been explored as building blocks for qubit architectures. One such design consists of vertically stacking two QDs to create a quantum dot molecule (QDM). The two dots can be resonantly tuned to form "molecule-like" coupled hole states from the hybridization of hole states otherwise localized in each respective dot. Furthermore, spin-mixing of the hybridized states in dots offset along their stacking direction enables qubit rotation to be driven optically, allowing for an all-optical qubit control scheme. Increasing the magnitude of this spin mixing is important for optical quantum control protocols. To enhance the tunnel coupling and spin-mixing across the dots, we introduce Bi in the GaAs inter-dot barrier. Previously, we showed how to model InAs/GaBiAs in an atomistic tight-binding formalism, and how the dot energy levels are affected by the alloy. In this paper, we discuss the lowering of the tunnel barrier, which results in a three fold increase of hole tunnel coupling strength in the presence of a 7% alloy. Additionally, we show how an asymmetric strain between the two dots caused by the alloy shifts the resonance. Finally, we discuss device geometries for which the introduction of Bi is most advantageous.

cond-mat.mes-hall↗

arXiv2018

Incorporation of random alloy GaBi$_x$As$_{1-x}$ barriers in InAs quantum dot molecules (I): energy levels and confined hole states

Self-assembled InAs quantum dots (QDs), which have long hole-spin coherence times and are amenable to optical control schemes, have long been explored as building blocks for qubit architectures. One such design consists of vertically stacking two QDs to create a quantum dot molecule (QDM) and using the spin-mixing properties of "molecule-like" coupled hole states for all-optical qubit manipulation. In this article, the first of two papers, we introduce the incorporation of dilute GaBiAs alloys in the barrier region between the two dots. GaBiAs is expected to increase the spin-mixing of the molecular states needed for qubit operations by raising the barrier valence band edge and spin-orbit splitting. Using an atomistic tight-binding model, we compute the properties of GaBiAs and the modification of hole states that arise when the alloy is used in the barrier of an InAs QDM. An atomistic treatment is necessary to correctly capture non-traditional alloy effects such as the band-anticrossing valence band. It also allows for the study of configurational variances and clustering effects of the alloy. We find that in InAs QDMs with a GaBiAs interdot barrier, electron states are not strongly affected by the inclusion of Bi. However, hole states are much more sensitive to the presence and configuration of Bi in the barriers. By independently studying the alloy-induced strain and electronic scattering off Bi and As orbitals, we conclude that an initial increase in QDM hole state energy at low Bi concentration is caused by the alloy-induced strain. We further find that the decrease in QDM hole energy at higher Bi concentrations can only be explained when both alloy strain and orbital effects are considered. In our second article, we use the understanding developed here to discuss how the alloyed barriers contribute to enhancement in hole spin-mixing and the implications for QDM qubit architectures.

cond-mat.mes-hall↗