Semiconductor Devices for Entangled Light Generation

Measurement of one of the photons in an entangled pair alters the quantum state of the other, even if they are separated by 1000's of km. Einstein described this peculiar property as 'spooky action at a distance'. As well as allowing the postulates of quantum theory to be tested, sources of entangled photons are an essential resource for applications in quantum information technology. For example, they enable quantum teleportation, the protocol used to transfer quantum information in a quantum communication system or quantum computer.
Though entanglement has many potential uses, there is currently no 'off-the-shelf' source of entangled photons. Lab experiments on entanglement often rely on pumping weak, non-linear processes in an insulating crystal with a powerful laser. However, recent work has shown that entangled photons can be produced by simple optically or electrically-driven semiconductor devices.[1,2]
The project will begin by characterizing individual quantum dots by micro-photoluminescence spectroscopy. The quantum dots are produced by the droplet epitaxy method, which is promising for use in entangled photon sources, due to their symmetric shape. The project will measure the exciton transition energies and polarisation splittings and relate this to the electronic structure of the dots.
The PhD will conduct research on novel semiconductor devices for generating entangled photons. The objective will be to develop sources that are useful for quantum information applications, ie. displaying high entanglement fidelity, photon indistinguishability and emission efficiency. The sources will be optimized and applied to different applications in quantum communications, such as quantum teleportation,[3,4] entanglement swapping and quantum repeaters. In the latter stages the sources will be implemented on installed fibre in the UK Quantum Network.
The work is mostly experimental, although could involve a significant amount of theory. It will involve fabrication of semiconductor devices using e-beam and photolithography, as well as the characterisation of these devices by optical spectroscopy, quantum state tomography and other experiments in quantum optics. The project will use state-of-the-art facilities at Toshiba Research Europe Ltd in Cambridge.