Abstract
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.
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We acknowledge partial funding by NSA/ARO and ONR.
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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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DOI: https://doi.org/10.1038/nphys882
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