Voltage controlled exchange energies of a two electron silicon double quantum dot with and without charge defects in the dielectric

Quantum dots are artificial atoms used for a multitude of purposes. Charge defects are commonly present and can significantly perturb the designed energy spectrum and purpose of the dots. Voltage controlled exchange energy in silicon double quantum dots (DQD) represents a system that is very sensitive to charge position and is of interest for quantum computing. We calculate the energy spectrum of the silicon double quantum dot system using a full configuration interaction that uses tight binding single particle wavefunctions. This approach allows us to analyze atomic scale charge perturbations of the DQD while accounting for the details of the complex momentum space physics of silicon (i.e., valley and valley-orbit physics). We analyze how the energy levels and exchange curves for a DQD are affected by nearby charge defects at various positions relative to the dot, which are consistent with defects expected in the metal-oxide-semiconductor system.

Coherent electron transport by adiabatic passage in an imperfect donor chain

Coherent Tunneling Adiabatic Passage (CTAP) has been proposed as a long-range physical qubit transport mechanism in solid-state quantum computing architectures. Although the mechanism can be implemented in either a chain of quantum dots or donors, a 1D chain of donors in Si is of particular interest due to the natural confining potential of donors that can in principle help reduce the gate densities in solid-state quantum computing architectures. Using detailed atomistic modeling, we investigate CTAP in a more realistic triple donor system in the presence of inevitable fabrication imperfections. In particular, we investigate how an adiabatic pathway for CTAP is affected by donor misplacements, and propose schemes to correct for such errors. We also investigate the sensitivity of the adiabatic path to gate voltage fluctuations. The tight-binding based atomistic treatment of straggle used here may benefit understanding of other donor nanostructures, such as donor-based charge and spin qubits. Finally, we derive an effective 3 times 3 model of CTAP that accurately resembles the voltage tuned lowest energy states of the multi-million atom tight-binding simulations, and provides a translation between intensive atomistic Hamiltonians and simplified effective Hamiltonians while retaining the relevant atomic-scale information. This method can help characterize multi-donor experimental structures quickly and accurately even in the presence of imperfections, overcoming some of the numeric intractabilities of finding optimal eigenstates for non-ideal donor placements.