Phys. Rev. Appl. 6, 054013 (2016)

Gate-defined quantum dots in semiconductors have been identified as hosts for high-fidelity quantum bits, storing the information in the spin state of the trapped charges. However, reproducing the physical properties of the dots is still a challenging aspect of their fabrication, undermining the realistic prospects for the implementation of quantum-computing tasks based on these devices.

Now, Zajac et al. report on the fabrication of nine collinear quantum dots with reproducible properties. The researchers pattern an undoped Si/SiGe heterostructure with aluminium-based screening layers and electrodes defining the dots, whose chemical potential and mutual tunnel coupling are tuned independently. Three additional collinear dots are also defined and used as single-electron charge detectors. By performing measurements of conductance and pulsed-gate spectroscopy, the researchers observe narrow value distributions for the charging and orbital-excited energies of the nine dots considered. Sensitive real-time detection capabilities for tunnelling events, with effective bandwidth up to 30 kHz are also demonstrated.

The researchers perform single-shot readouts of an electron spin trapped in one of the dots, quantifying spin-relaxation times in the order of hundreds of milliseconds. Remarkably, they also demonstrate a strong capacitive coupling between adjacent dot couples — a convenient property in view of the implementation of high-frequency computing tasks.