The Search for Quantum Coherence in a Semiconductor

Semiconductors have underpinned the revolution in classical information technology. Semiconductors, particularly high quality heterostructures, have also underpinned the discovery of new physics in less than three dimesions. Improvements and refinements in both fields are on-going. But the next major challenge is the development of truly quantum devices, relying on the exploitation of a quantum mechanical superposition. Are semiconductors up to the job? Or is it time to abandon semiconductors in favour of another class of material?

Answering this question poses an immediate physics challencge with two fundamental aspects. First, dephasing the processes by which information stored in quantum superpositions is lost, must be understood. Secondly, devices need to be designed in which the dephasing is minimalized. In the solid-state, dephasing is rich and varied, reflecting the complexity of the solid state. However, particularly in a semiconductor, advanced heterostructure technology and post-growth nano-fabrication can be used to suppress the main dephasing mechanism, an interaction with the phonons. Furthermore, state-of-the-art experimental techniques can be applied to probe the complex interactions in the solid-state with unprecedented precision. The end point of there experiments is presently wide open.

Results will be presented which suggest that the key advantages of semiconductors (heterostructures, nano-fabrication) can result in coherent, optically-active quantum states. The key concept is to manipulate a single spin. The possibilities for shielding the single spin from charge noise and spin noise will be discussed. It will also be argued that future progress in the physics depends not just on semiconductor design but also on novel instrumentation and on an integration with other classes of materials; this too is a likely paradigm for a future quantum technology based on solid-state materials.