Singly doped colloidal quantum dots as optically addressed nanopositionable qubits

Colloidal quantum dots (CQDs) are isolated semiconductor nanocrystals with a size-tunable bandgap that can be prepared and processed by well-established solvent-based chemistry, and are currently used for a number of optoelectronic applications. When doped with a single atom, they also have great potential as a platform for optically addressable spin qubits. This perspective first describes the process by which doped CQDs can be made and the electronic structure produced in them by doping with a single atom. The properties that make them particularly well-suited as a spin-photon interface are identified: a local environment for the dopant that is free of unwanted spins; an optical cross-section for the dopant that can be enhanced by orders of magnitude via an exchange interaction with the band edge exciton of the dot; and, as an isolated nanocrystal, the scope for nano-positioning and hence precise incorporation into device structures. Lastly, two areas for development are discussed which would enhance the impact of singly doped quantum dots on quantum technology. The first of these is a synthetic method that ensures deterministic doping with single atoms and the second is to expand the range of dopants available.