We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling quantum devices, particularly Si double quantum dots (DQDs) developed for quantum computing. The simulator core includes Poisson, Schrodinger, and Configuration Interaction solvers which can be run individually or combined self-consistently. The simulator is built upon Sandia-developed Trilinos and Albany components, and is interfaced with the Dakota optimization tool. It is being developed for seamless integration, high flexibility and throughput, and is intended to be open source. The QCAD tool has been used to simulate a large number of fabricated silicon DQDs and has provided fast feedback for design comparison and optimization.
We have compared simulations using solutions of Poisson's equation to detailed capacitance measurements on a double quantum dot structure. We tabulate the results and show which cases show good agreement and which do not. The capacitance values are also compared to those calculated by a solution of Laplace's equation. Electron density is plotted and discussed. In order to understand relevant potential barriers we compare simulations at 50 Kelvin to simulations at 15 Kelvin. We show that the charge density does not differ greatly, but that the conduction band potential does. However, a method of estimating the potential at 0 Kelvin based on the charge distribution at 50 Kelvin is shown to be close to the potential at 15 Kelvin. This method was used to estimate potential barriers at 0 Kelvin in two quantum dot structures.