Probing Localized Charge States in Atom-based Silicon Quantum dot Arrays using RF Reflectometry

Hydrogen-based scanning probe lithography allows for deterministic placement of individual dopant atoms which is crucial for fabricating arrayed few-donor devices used as analog quantum simulators. However, precisely controlling exact donor numbers on individual site remains a big challenge. Together with variable tunnel coupling/exchange interaction between sites, current 2D dopant quantum dot arrays in silicon still include significant disorder in the framework of the Fermi-Hubbard model. Anderson localization combined with many-body long range Coulomb effects can produce localized charge states which prevent the array from conducting even at strong tunnel coupling.

In this talk, we show transport and RF reflectometry measurements on dopant arrays (2x2 and 3x3) to extract charge occupation. Localized charge states may show little or no conductance but can be revealed by RF reflectometry measurements with a LC tank circuit attached to the source. We extract the energy addition spectrum for these states and explore the spin-filling sequence within the arrays. Using an extended Hubbard model, we simulate the spin/charge occupation, the spatial distribution of the many-body states and the electron addition energy spectrum with realistic disorder.