Optical shaping of the polarization anisotropy in a laterally coupled quantum dot dimer.

We find that the emission from laterally coupled quantum dots is strongly polarized along the coupled direction [1$$\bar 1$$0], and its polarization anisotropy can be shaped by changing the orientation of the polarized excitation. When the nonresonant excitation is linearly polarized perpendicular to the coupled direction [110], excitons (X1 and X2) and local biexcitons (X1X1 and X2X2) from the two separate quantum dots (QD1 and QD2) show emission anisotropy with a small degree of polarization (10%). On the other hand, when the excitation polarization is parallel to the coupled direction [1$$\bar 1$$0], the polarization anisotropy of excitons, local biexcitons, and coupled biexcitons (X1X2) is enhanced with a degree of polarization of 74%. We also observed a consistent anisotropy in the time-resolved photoluminescence. The decay rate of the polarized photoluminescence intensity along the coupled direction is relatively high, but the anisotropic decay rate can be modified by changing the orientation of the polarized excitation. An energy difference is also observed between the polarized emission spectra parallel and perpendicular to the coupled direction, and it increases by up to three times by changing the excitation polarization orientation from [110] to [1$$\bar 1$$0]. These results suggest that the dipole–dipole interaction across the two separate quantum dots is mediated and that the anisotropic wavefunctions of the excitons and biexcitons are shaped by the excitation polarization. New information storage technologies could use polarized light to control the optical properties of coupled quantum dots. The idea of combining quantum dots – nanoscale semiconductor crystals – into coupled pairs has attracted great attention due to the increased number of exotic quantum states that can be realized for storing data. Robert Taylor at the University of Oxford, UK, with co-workers in China and Korea, directed polarized laser light onto coupled gallium arsenide quantum dots to induce photoluminescence. They found that the emitted light showed very different characteristics depending on whether the excitation was parallel or at right angles to the line formed by the two dots. This ‘optical shaping’ reflects different arrangements of excitons – bound states of electrons and holes – in the coupled dots, and could open new avenues for data storage and thermoelectric energy harvesting.