QTCAD (Quantum-Technology Computer-Aided-Design) is a finite-element (FEM) simulator used to predict the performance of spin-qubit devices before their production. QTCAD simulations can lead to huge savings in both time and money since they allow users to explore many design scenarios before their implementation in the lab.
Gated geometries can be imported directly from standard layout (.gds) files used to design integrated circuits [layout.png]. Heterostructure stacks are defined through our simple Python API. This approach captures the geometry of most gated quantum dots. For expert users, arbitrary 2D and 3D geometries and their corresponding mesh can be defined and customized at will using Gmsh.
QTCAD’s non-linear Poisson solver can predict the confinement potential of quantum dots in semiconductor nanostructures under split gates. QTCAD is designed to converge at sub-Kelvin temperatures in many practical spin-qubit designs. Low-temperature convergence is notoriously difficult with other currently available TCAD software.
QTCAD’s Schrödinger solver calculates the wave functions of electrons or holes in realistic confinement potentials. These confinement potentials are determined by applying QTCAD’s non-linear Poisson solver to specific device geometries. Thus the computed wavefuntions can be used to predict if a given candidate device can host bound states.
QTCAD can assemble and exactly diagonalize the many-body Hamiltonian for few-electron or few-hole systems under quantum confinement using a truncated basis built from real-space single-body eigenfunctions of the device. This approach yields accurate chemical potentials and addition-energy spectra for realistic quantum dots accounting for the Coulomb interaction between confined electrons or holes.
Our master equation solver leverages QTCAD’s many-body physics capabilities to calculate the current flowing through quantum-dot systems in the sequential tunneling regime. This enables the treatment of Coulomb blockade and the prediction of charge stability diagrams used to demonstrate the few-electron or few-hole regime in experiments.
For silicon-based devices, lifting the valley degeneracy is a vital step to isolate well-defined qubit eigenstates. QTCAD includes a module that calculates valley splitting due to sharp heterostructure interfaces using matrix elements in the basis of Bloch states calculated with our atomistic simulation software RESCU.
Ultimately, QTCAD determines the system Hamiltonian, accounting for realistic device geometry. Once the system Hamiltonian is known, qubit time-evolution can be evaluated using third-party time-dependent Schrödinger solvers (e.g., QuTiP). In this figure, we show Rabi oscillations for a spin-qubit device under electric-dipole spin resonance. We account for a realistic inhomogeneous magnetic field, and for the precise geometry of electric fields acting on the quantum dot due to applied and charge-noise-induced gate potentials.
Interface with our large scale DFT software RESCU to calculate material parameters that enter the k.p theory.
QTCAD can easily be deployed on Linux, MacOS, and Windows machines, on personal computers and clusters alike.
Current beta version of QTCAD is 0.7.0.
To access to QTCAD user documentation, click the link below: installation and user manuals, tutorials, theory and technical information pages are all there for your support and to get you up to speed as quickly as possible.
