Full control of quadruple quantum dot circuit charge states in the   single electron regime
  We report the realization of an array of four tunnel coupled quantum dots in the single electron regime, which is the first required step toward a scalable solid state spin qubit architecture. We achieve an efficient tunability of the system but also find out that the conditions to realize spin blockade readout are not as straightforwardly obtained as for double and triple quantum dot circuits. We use a simple capacitive model of the series quadruple quantum dots circuit to investigate its complex charge state diagrams and are able to find the most suitable configurations for future Pauli spin blockade measurements. We then experimentally realize the corresponding charge states with a good agreement to our model. 
M. R. Delbecq, T. Nakajima, T. Otsuka, S. Amaha, J. D. Watson, M. J.   Manfra, S. Tarucha
cond-mat.mes-hall