Quantum computing with hot silicon and fast germanium qubits

The prospect of building quantum circuits using advanced semiconductor manufacturing positions quantum dots as an attractive platform for quantum information processing. Extensive studies on various materials have led to demonstrations of two-qubit logic in gallium arsenide, silicon, and germanium. However, interconnecting larger numbers of qubits in semiconductor devices has remained an outstanding challenge. Here, I will present our group efforts based on silicon and germanium quantum dots and wills show the realization of a two-dimensional four-qubit quantum processor based on hole spins in germanium quantum dots. Qubit logic is implemented all-electrically and the exchange interaction can be pulsed to freely program one-qubit, two-qubit, three-qubit, and four-qubit operations, resulting in a compact and high-connectivity circuit. A quantum logic circuit that generates a four-qubit Greenberger-Horne-Zeilinger state is executed and coherent evolution is obtained by incorporating dynamical decoupling. I will furthermore discuss opportunities and challenges for quantum dot qubits, such as operation at comparatively high temperatures as a step toward integrated quantum circuits.