We report the realization of an array of four tunnel coupled quantum dots inthe single electron regime, which is the first required step toward a scalablesolid state spin qubit architecture. We achieve an efficient tunability of thesystem but also find out that the conditions to realize spin blockade readoutare not as straightforwardly obtained as for double and triple quantum dotcircuits. We use a simple capacitive model of the series quadruple quantum dotscircuit to investigate its complex charge state diagrams and are able to findthe most suitable configurations for future Pauli spin blockade measurements.We then experimentally realize the corresponding charge states with a goodagreement to our model.
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