Electron spins in quantum dots form ideal two-level systems for implementing quantum computation in the solid state. While spin states can have extremely long quantum coherence times, addressing single spins and coupling large arrays of spins have been formidable experimental challenges. Research over the past several decades has resulted in a variety of creative approaches to address these problems, yielded new insights into the physics of spins in semiconductors, and demonstrated many of the basic criteria for quantum computation.
This thesis presents a systematic study of the physics and quantum control of spins in few-electron Si/SiGe quantum dots. We present novel designs for quantum dot devices that yield improved control of single electron wavefunctions. We demonstrate full control of single electron spin states by placing a quantum dot in the vicinity of a strong magnetic field gradient produced by a micron-scale ferromagnet, and quantify the control fidelity using randomized benchmarking. Utilizing the exchange interaction between neighboring spins in combination with arbitrary single-spin rotations, we present one of the first demonstrations of all the criteria for universal quantum computation (initialization, readout, and a universal set of gates) with electron spins in a single device. Finally, we take the first steps towards controlling a large array of quantum dots by deterministically shuttling single electrons through an array of nine quantum dots.