Progress towards two double-dot qubits in Si/SiGe: quadruple quantum dots

We present the fabrication and electrical characterization of two types of gate-defined quadruple quantum dot devices formed in Si/SiGe heterostructures. We compare two designs, one which uses three layers of tightly overlapping gates and is similar to the work found in [1], and one which uses only two layers of gates and has significantly more open space between neighboring gates [2]. We demonstrate charge-state conditional quantum oscillations in the more open device, we compare the tunability of both devices with each other, and we discuss the implications of these measurements on a path towards larger numbers of coupled quantum dot qubits. This work is supported in part by ARO (W911NF-12-1-0607), NSF (DMR-1206915, PHY-1104660), ONR (N00014-15-1-0029) and the Department of Defense. Development and maintenance of the growth facilities used for fabricating samples supported by DOE (DE-FG02-03ER46028). DK acknowledges support from the Korea Institute of Science and Technology Institutional Program (Project No. 2E26681). This research utilized facilities supported by the NSF (DMR-0832760, DMR-1121288). [1] D. M. Zajac \textit{et al}., \textit{Appl. Phys. Lett. }\textbf{106}, 223507 (2015). [2] D. R. Ward \textit{et al.}, \textit{npj Quant. Inf.} \textbf{2}, 16032 (2016).