Strategies for Automated Tune-up of Quantum Dot Arrays

As quantum dot qubit devices grow beyond two or three dots, computer-aided tools for calibration and control become essential. The first stage in tuning up any quantum dot spin qubit is determining an appropriate set of voltage biases such that all dots are loaded in the desired charge configuration, a task which is already complex at the three-dot level. In this talk we describe an automated process, based on single-dot measurements, simple image analysis, and linear compensation modeling of the device, which enables estimation of arbitrary charge states for a multi-dot system. Crucially, the desired bias state is estimated in a way that keeps all inter-dot tunneling rates within an acceptable range. This ensures relevant charge transitions remain visible, even for dots far away from the electron reservoir, and allows navigation of subsequent charge stability diagrams using image processing techniques. We demonstrate that this method can fully automate tuning of a six dot Si/SiGe device into a configuration appropriate for exchange-only qubit operation, including location of appropriate bias windows for spin preparation and measurement, and a validating demonstration of coherent spin rotations.