Hole-spin mixing in InAs quantum dot molecules

The spin state of holes confined in single InAs quantum dots have recently emerged as a promising system for the storage or manipulation of quantum information. These holes are often assumed to have no mixing between orthogonal heavy-hole-spin projections (in the absence of a transverse magnetic field). The same assumption has been applied to InAs quantum dot molecules formed by two stacked InAs quantum dots that are coupled by coherent tunneling of the hole between the two dots. We present experimental evidence of the existence of a hole-spin-mixing term obtained with magnetophotoluminescence spectroscopy on such InAs quantum dot molecules. We use a Luttinger spinor model to explain the physical origin of this hole-spin-mixing term: misalignment of the dots along the stacking direction breaks the angular symmetry and allows mixing of the heavy-hole components through the light-hole component of the spinor. We discuss how this spin-mixing mechanism may offer new spin manipulation opportunities that are unique to holes.