Atomic-scale control of tunneling in donor-based devices
Xiqiao Wang, Jonathan E. Wyrick, Ranjit V. Kashid, Pradeep N. Namboodiri, Scott W. Schmucker, Andrew Murphy, Michael D. Stewart, Richard M. Silver
Atomically precise donor-based quantum devices are a promising candidate for scalable solid- state quantum computing. Atomically precise design and implementation of the tunnel coupling in these devices is essential to realize gate-tunable exchange coupling, electron spin initialization and readout, and ultrasensitive spin and charge sensing. Current efforts in atomically precise lithography have enabled deterministic placement of single dopant atoms into the Si lattice with sub-nm precision. However, critical challenges in atomically precise fabrication have meant an absence of systematic atomic-scale control of tunnel coupling. Here we demonstrate the exponential dependence of tunnel resistance on the junction size in atomically precise single electron transistors (SETs). Using the naturally occurring Si (100) 2x1 surface reconstruction lattice as an atomically-precise ruler, we systematically vary the number of lattice counts within the tunnel junction gaps and demonstrate exponential scaling of the tunnel resistance at the atomic limit. Combining low-temperature transport measurements with single electron tunneling simulations, we characterize the tunnel coupling asymmetry resulting from atomic scale imperfections in the tunnel junctions. Our results demonstrate the key capability to do atom-scale design and engineering of the tunnel coupling necessary for solid-state quantum computing and analog quantum simulation.