Few-Electron Quantum Dot Circuit with Integrated Charge Read-Out
  We report on the realization of a few-electron double quantum dot defined in a two-dimensional electron gas by means of surface gates on top of a GaAs/AlGaAs heterostructure. Two quantum point contacts (QPCs) are placed in the vicinity of the double quantum dot and serve as charge detectors. These enable determination of the number of conduction electrons on each dot. This number can be reduced to zero while still allowing transport measurements through the double dot. Microwave radiation is used to pump an electron from one dot to the other by absorption of a single photon. The experiments demonstrate that this quantum dot circuit can serve as a good starting point for a scalable spin-qubit system. 
J. M. Elzerman, R. Hanson, J. S. Greidanus, L. H. Willems van Beveren,   S. De Franceschi, L. M. K. Vandersypen, S. Tarucha,...