Spin qubits: Control, calibration and readout in multi-qubit arrays*

Encoding quantum information in the spins of electrons or holes confined in semiconductor quantum dots is a promising technology, due to their long coherence times, inherent gate-voltage tunability and compatibility with industrial foundry fabrication. As these quantum systems are scaled up in linear and two-dimensional arrays to form NISQ processors, the density of gate electrodes can lead to more and more operational complexity. In this talk, I will present four directions of active research. First, I will present advances in multi-gate-layer fabrication of qubits implemented in academic facilities, as well as in industrial foundries focusing on spin-based quantum processors. Second, I will present our work on implementing fast, high-fidelity and simultaneous qubit readout, in particular involving RF-reflectometry, across small arrays of quantum dots. Third, I will discuss the importance of methods such as the implementation of automated tuning, loading and calibration of gate-voltage controlled arrays of quantum dots. Lastly, I will showcase functionalities enabled by new techniques of quantum control, such as real-time fast feedback using FPGA-based machinery that enables online, closed-loop control and calibration of quantum systems. These efforts utlize high-quality heterostructures in silicon, germanium, and gallium arsenide quantum wells, as well as devices made using industrial CMOS processes on large-scale 300mm wafers. I will also discuss the current need, and future prospects, for techniques such as crosstalk mitigation, multi-qubit pulse calibration, sensor compensation, virtual gating, and adaptive readout. The near-term goal is to engineer scalable spin qubit networks demonstrating stable and coherent qubit arrays for computation, as well as for the simulation of phenomena relevant for fundamental physics and chemistry applications.