Semiconductor quantum dots have optical properties similar to simple atomic systems, unlike higher dimensional semiconductor structures that are dominated by manybody physics associated with the continuum states. They also provide a potentially ideal electronic structure appropriate for quantum computing. The data shows that these structures can be coherently controlled on a time scale short compared to the quantum decoherence time and that entangled states of qubits (represented by exciton optical Bloch vectors) can be created. The system is remarkably robust against pure dephasing and we have been able to demonstrate a simple conditional quantum logic device involving multiple Rabi flops of the exciton and biexciton.

The future of this work lies in coherence engineering of the materials to provide longer coherence times for the qubits. To this end, our group is now working on single electron doped quantum dots where the spin, with long coherence time, is the qubit. Measurements show that we can coherently control the spin state of a single electron.