Controlling Number of Dopants per Site in Si:P Quantum Devices

STM-based fabrication of atomically precise Si:P structures has been demonstrated as a promising platform for the realization of dopant-based qubit quantum computing. There is a growing broader interest in applying this technique to other quantum systems in Si, for example artificial lattices to engineer band structure, as well as arrays of atoms acting as tunable Hubbard simulators. We present results from a single-atom transistor and few-atom cluster transistors demonstrating the effect that the number of dopants per site has on the energy spectrum of these devices, with the important implication that for many applications of interest it will be necessary to control this parameter with absolute precision. We detail our efforts using STM-based feedback-controlled techniques to engineer placement and number of dopants per site with the goal of reducing the fabrication uncertainty of dopants per site to zero.