Hole spins in an InAs/GaAs quantum dot molecule subject to lateral electric fields

Abstract

There has been tremendous progress in manipulating electron and hole spin states in quantum dots or quantum dot molecules (QDMs) with growth-direction (vertical) electric fields and optical excitations. However, the response of carriers in QDMs to an in-plane (lateral) electric field remains largely unexplored. We computationally explore spin-mixing interactions in the molecular states of single holes confined in vertically-stacked InAs/GaAs QDMs using atomistic tight-binding simulations. We systematically investigate QDMs with different geometric structure parameters and local piezoelectric fields. We observe both a relatively large Stark shift and a change in the Zeeman splitting as the magnitude of the lateral electric field increases. Most importantly, we observe that lateral electric fields induce hole spin mixing with a magnitude that increases with increasing lateral electric field over a moderate range. These results suggest that applied lateral electric fields could be used to fine-tune and manipulate, in situ, the energy levels and spin properties of single holes confined in QDMs.

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

“…The orange line and dots in Figure a show how the magnitude of hole spin mixing (Δ sm ) and the vertical electric field of the hole spin mixing resonance ( F sm ) change as a function of the x ‐direction lateral electric field. The results show that Δ sm increases linearly from zero with the lateral electric field, while F sm shifts due to reduced Zeeman splitting . Further calculations show that lateral electric field can also tune the hole spin mixing magnitude in a CQD with a 1 nm lateral offset.…”

“…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.…”

“…Ma et al. then show that hole spin mixing can be turned on in a perfectly symmetric quantum dot by applying a constant lateral electric field . The orange line and dots in Figure a show how the magnitude of hole spin mixing (Δ sm ) and the vertical electric field of the hole spin mixing resonance ( F sm ) change as a function of the x ‐direction lateral electric field.…”

“…Even if hole spin mixing can be maximized via barrier composition and controlled lateral offsets between QDs, post‐growth tuning of the hole spin mixing magnitude is needed to actively enhance or suppress the coupling rate during quantum device operations. Ma et al . recently shown that externally applied electric fields provide a means to realize this in situ control.…”

“…The value of the electric field where hole spin mixings happen is labeled as F sm , and the magnitude is labelled as Δ sm . Adapted with permission . Copyright 2016, American Physical Society.…”