Quantum engineering at the silicon surface using dangling bonds

Individual atoms and ions are now routinely manipulated using scanning tunnelling microscopes or electromagnetic traps for the creation and control of artificial quantum states. For applications such as quantum information processing, the ability to introduce multiple atomic-scale defects deterministically in a semiconductor is highly desirable. Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface. We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image. Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy. The ability to add and move individual atoms on a surface with a scanning tunnelling microscope enables precise control over the electronic quantum states of the surface. Schofield et al. show that removing hydrogen atoms from a passivated silicon surface can be used to generate and control such states.