Quantum-information processing with ferroelectrically coupled quantum dots

A proposal is described to construct a quantum-information processor using ferroelectrically coupled Ge/Si quantum dots. The spin of single electrons form the fundamental qubits. Small-diameter (<10 nm) Ge quantum dots are optically excited to create spin-polarized electrons in Si. The static polarization of an epitaxial ferroelectric thin film confines electrons laterally in the semiconductor; spin interactions between nearest-neighbor electrons are mediated by the nonlinear process of optical rectification. Single-qubit operations are achieved through ``g-factor engineering'' in the Ge/Si structures; spin-spin interactions occur through Heisenberg exchange, controlled by ferroelectric gates. A method for reading out the final state, while required for quantum computing, is not described; approaches involving single-electron transistors may prove fruitful in satisfying this requirement.