Deterministic Atom Placement by Ion Implantation: Few and Single Atom Devices for Quantum Computer Technology

Abstract

We describe an approach to quantum computer technology based on engineered single donor atoms implanted into silicon. We exploit quantum superposition and entanglement in potentially scalable nanoscale quantum devices engineered with just a single phosphorus donor atom in a silicon nano-scale complementary metal-oxide-semiconductor device. The devices are sensitive to the variation in the position of the donor atoms and also, when cooled to 100 mK, to the quantum state of single donors. Over the past two years we have fabricated devices incorporating 31P donor atoms implanted 20 nm deep into isotopically enriched 28Si followed by rapid thermal annealing at 1000oC for 5 s to activate the donors and minimise diffusion. Measurement of a single ionized donor gives the 31P nuclear spin (I=1/2) coherence time greater than 30 seconds showing exceptional promise and the robustness of this quantum system despite the influence of the nearby gate oxide and electrode metals. To implant donor atoms in a large-scale device we have developed a deterministic ion implantation method that is cited by the 2011 International Semiconductor Roadmap. We exploit signals arising from the ion induced charge from single implants in the substrate detected by on-chip detector electrodes. We describe our approach to take this technology to the next stage by building deterministic arrays of single atoms with the goal of sub-10 nm positioning precision as a pathway to a large scale device that could form the building block of a future CMOS quantum computer fabricated with the standard tools of the industry.