Modelling Exchange in Silicon Quantum Dots

A challenge for modelling quantum dot spin qubits in silicon is the quantitative estimation of the exchange energy J over a wide range of electrostatic potentials. Approximate methods such as Heitler-London and Hund-Milliken are often applied to GaAs dots, but break down in silicon due to the larger effective mass of the electron. I will discuss our progress towards building a simulation toolbox for exchange energies based on configuration interaction (CI) methods commonly used in quantum chemistry. A finite-element solver simulates the potential landscape of silicon MOSFET double quantum dots as a function of applied gate potentials, and the results are input to a CI code to calculate the two-electron eigenstates and energies. While the present calculations assume a single valley state, the CI methods can be extended to properly account for multiple valley states. I will also give a brief overview of our group’s experimental program, including quantum transport in nanowires, carbon nanotubes, and silicon quantum dots.