Incorporation of random alloy GaBixAs1−x barriers in InAs quantum dot molecules: Energy levels and confined hole states

Abstract

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 paper, the first of two papers, we introduce the incorporation of dilute GaBixAs1−x alloys in the barrier region between the two dots. GaBixAs1−x 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 GaBixAs1−x 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 paper, 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. arXiv:1810.09483v2 [cond-mat.mes-hall]

Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies

“…As discussed in Section 8, hole spin mixing originates in the spin–orbit interactions within the valence band and requires symmetry breaking. In a vertically coupled CQD, this symmetry breaking arises naturally from lateral misalignment between the two QDs; the magnitude of the hole spin mixing parameter is proportional to the magnitude of the misalignment . As reported by Doty et al., randomly grown CQDs often have a lateral misalignment between 0 and 4 nm.…”

“…For example, lowering the potential barrier for hole confinement would lead to increased tunneling rates for the heavy hole/light hole wavefunctions. Lin et al . recently calculated the state energies that could be realized if Bi were introduced into the GaAs barrier separating the two QDs, lowering the valence band edge.…”

The magneto-optics in quantum wires comprised of vertically stacked quantum dots: A calling for the magnetoplasmon qubits

“…Immediately upon being noticed due to the device potential, this discovery ignited an explosion in investigation into the physics of quantum dots and a large number of groups became active embarking on a variety of research interests. The result was a long list of experimental [29][30][31][32][33][34][35][36][37][38] and theoretical [39][40][41][42][43][44][45][46][47][48] works dealing with elastic, thermal, electrical, magnetic, electronic, and optical phenomena, which motivated authors to envisage various solid-state devices. Early efforts had largely focused on the pairs of VSQD separated by thin barrierstermed quantum dot molecules (QDM) -because of their importance in realizing the short-distance quantum-state transfer, which is essential for the future quantum communication networks.…”