Lateral Quantum Dot molecule - towards electric field controlled quantum gate

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The goal of this project is the controlled positioning and optical characterisation of interacting semiconductor quantum dots closely spaced in lateral direction, i.e. of lateral quantum dot molecules (QDMs). The exact positioning of the lateral QDMs will be achieved by growth on pre-patterned GaAs (001) substrates, which we plan to produce by ex-situ lithography and reactive ion etching. The lateral QDMs consist of InAs/GaAs as well as GaAs/AlGaAs quantum dots (QDs). By means of single QD luminescence and tunnelling spectroscopy the electronic coupling between charge carriers in neighbouring QDs will be investigated. The coupling strength will be systematically studied by applying an electric field in lateral direction. In order to tune the strength of the interaction between the QDs composing a QDM, a gate electrode will be accurately positioned above the QDM. The QDM properties will be then investigated as a function of gate voltage. This is a necessary step towards the demonstration of basic logic operations and the fabrication of a semiconductor quantum gate.