Multiqubit operation in arrays of gate defined semiconductor quantum dots

Building a fault-tolerant quantum computer will require integrating millions of high-quality qubits. Among the leading approaches, semiconductor spin qubits are particularly attractive because they combine long coherence times [1], high-fidelity operation [2], and compatibility with industrial Complementary Metal-Oxide-Semiconductor (CMOS) manufacturing processes [3-5]. By leveraging the same fabrication technologies that enabled classical integrated circuits to scale to billions of transistors, we can foresee a path toward large-scale quantum processors with high yield and integration with classical electronics. In this seminar, I will discuss recent progress in using the spin states of single electrons confined in semiconductor gate-defined quantum dots as qubits. I will begin by reviewing the principles of spin control and readout, highlighting how high-fidelity single- and two-qubit operations can be achieved in these systems [2]. I will then discuss how quantum dots can be assembled into larger arrays capable of multiqubit operations [6]. Finally, I will outline the key engineering challenges (and opportunities) that must be overcome (explored) to transform these nanoscale devices into large-scale quantum processors. [1] Veldhorst, Menno, et al. "An addressable quantum dot qubit with fault-tolerant control-fidelity." Nature nanotechnology 9.12 (2014): 981-985. [2] Xue, Xiao, et al. "Quantum logic with spin qubits crossing the surface code threshold." Nature 601.7893 (2022): 343-347. [3] Zwerver, Anne-Marije J., et al. "Qubits made by advanced semiconductor manufacturing." Nature Electronics 5.3 (2022): 184-190. [4] George, Hubert C., et al. "12-spin-qubit arrays fabricated on a 300 mm semiconductor manufacturing line." Nano Letters 25.2 (2024): 793-799.   [5] Steinacker, Paul, et al. "Industry-compatible silicon spin-qubit unit cells exceeding 99% fidelity." Nature 646.8083 (2025): 81-87.   [6] Fernández de Fuentes, I., et al. "Running a Six-Qubit Quantum Circuit on a Silicon Spin-Qubit Array." PRX Quantum 7.1 (2026): 010308.