Optically mapping the electronic structure of coupled quantum dots

Abstract

Arrays of quantum dots can be useful for building ‘artificial molecules’, and potentially as elements of quantum information networks. But in practice, no two dots are the same. An optical technique provides the means for in situ characterization of individual dots, and their collective properties. In a network of quantum dots1 embedded in a semiconductor structure, no two are the same, and so their individual and collective properties must be measured after fabrication. Here, we demonstrate a ‘level anti-crossing spectroscopy’ (LACS) technique in which the ladder of orbital energy levels of one quantum dot is used to probe that of a nearby quantum dot. This optics-based technique can be applied in situ to a cluster of tunnel-coupled dots, in configurations similar to that predicted for new photonic or quantum information technologies2,3,4,5. Although the lowest energy levels of a quantum dot are arranged approximately in a shell structure6,7,8,9,10, asymmetries or intrinsic physics—such as spin–orbit coupling for holes—may alter level splittings significantly11. We use LACS on a diatomic molecule composed of vertically stacked InAs/GaAs quantum dots and obtain the excited-state level diagram of a hole with and without extra carriers. The observation of excited molecular orbitals, including σ and π bonding states, provides fresh opportunities in solid-state molecular physics. Combined with atomic-resolution microscopy and electronic-structure theory for typical dots, the LACS technique could also enable ‘reverse engineering’ of the level structure and the corresponding optical response12.

Cite this article

Scheibner, M., Yakes, M., Bracker, A. et al. Optically mapping the electronic structure of coupled quantum dots. Nature Phys 4, 291–295 (2008). https://doi.org/10.1038/nphys882

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