Electrical identification of single dopant atoms

Is it possible to design a solid-state electronic device with functionality based on the electronic occupancy, orbital-state or spin-state of a single atom? A positive answer could enable the ultimate miniaturisation of semiconductor devices. With this question in mind we will identify individual dopant atoms (intentionally added impurities) in silicon nanostructures and then determine the lifetime of their quantum mechanical spin states.Our main experimental technique to detect dopant atoms is ultra-sensitive charge detection using the single electron transistor. This will enable us to determine whether an electron resides on a randomly positioned dopant, or if the dopant is in its ionised state. Using radio-frequency techniques we will be able to measure this occupancy in a millionth of a second. On its own, this would only tell us that a dopant atom (or charge trap) is present but nothing of its identity. The key is to combine our charge detection technique with a means of spectroscopy. Electron spin resonance is a suitable technique, capable of identifying the unique spin environment of each species of impurity atom. To aid us we will collaborate with an expert in electron spin resonance, Prof. Martin Brandt at Walter Schottky Institute.Once we have identified a dopant atom we will use electron spin resonance not as a spectroscopy technique but to control its electron spin state. A similar technique has already been used in the case of electrons bound in quantum dots - devices often known as 'artificial atoms'. In this way we will be able to measure the quantum mechanical spin lifetimes of a single electron in silicon. Electron spins in silicon are known, from ensemble measurements, to be long-lived when compared to most other materials. Due to this longevity they are excellent candidates to be qubits - the building blocks of a quantum mechanical computer.