Progress in silicon-based quantum computing

The progress at the Australian Centre for Quantum Computer Technology towards the fabrication and demonstration of spin qubits and charge qubits based on phosphorus donor atoms embedded in intrinsic silicon is reviewed. Fabrication is being pursued via two complementary pathways: a `top-down' approach for near-term production of few-qubit demonstration devices and a `bottom-up' approach for large-scale qubit arrays with sub-nanometre precision. The `top-down' approach employs a low-energy (keV) ion beam to implant the phosphorus atoms. Single-atom control during implantation is achieved by monitoring on-chip detector electrodes, integrated within the device structure. In contrast, the `bottom-up' approach uses scanning tunneling microscope lithography and epitaxial silicon overgrowth to construct devices at an atomic scale. In both cases, surface electrodes control the qubit using voltage pulses, and dual single-electron transistors operating near the quantum limit provide fast read-out with spurious-signal rejection