Characterization of accumulation-mode Si/SiGe triple quantum dots

The transition from quantum dots fabricated from doped Si/SiGe quantum wells to undoped accumulation-mode structures has greatly improved the performance of few-electron quantum dots. Our accumulation-mode devices\footnote{D. M. Zajac \textit{et al.}, Appl. Phys. Lett. \textbf{106}, 223507 (2015).} are reconfigurable and allow for operation as single, double, or triple quantum dots. In these devices, we measure typical charging energies $E_{\mathrm{c}}= 5.7$ meV, orbital excited state energies as large as $E_{\mathrm{o}}$ = 2.9 meV, and valley splittings of up to $E_{\mathrm{v}}= 80$ $\mu$eV. With the device configured as a triple quantum dot, we easily reach the (1,1,1) charge configuration. The gate architecture allows the interdot tunnel coupling to be tuned over a wide range, which is important for operation as an exchange-only spin qubit.\footnote{ J. Medford \textit{et al.}, Phys. Rev. Lett. \textbf{111}, 050501 (2013).}