Optical single-electron spin detector.

For the exploration of electron spin in quantum information processing, a capability to detect their spin states (up/down in some basis) is essential. While there are well-established methods for electrical and optical spin detection in confined systems, a spin detection technique for travelling electrons is yet to be developed. This project will develop a spin detection technique for travelling electron wave packets, which would enable the use of single-electron wave packets as flying qubits interconnecting stationary qubit elements, as well as the generation of entangled photon pairs. The single-electron wave packets will be generated, on-demand, from a semiconductor quantum dot. These wave packets will be transported through quantum-Hall edge states to a p-type region created on the same substrate. When the electrons recombine with holes, photons will be generated and their circular polarisation states will depend on the electron spin states. Therefore, this new technology will be based on single-electron device technology and a lateral p-n junction developed jointly by the Quantum Detection Group at NPL and the Semiconductor Physics Group at the Cavendish Laboratory in Cambridge.