Quantum dots are fast becoming the dominate discrete single and entangled photon source. They have high quantum efficiency, meaning they produce nearly one photon per pumping clock cycle. They also have fast decay rates so that the single or entangled photon emission rate can be in the GHz regime. They can be inserted into micrometre-scale optical cavities to focus photon emission into an optical that can be easily coupled into optical fibres or a free-space system. The problem is the coherence time of the spin in the ground state of the quantum dot system. Its coherence time is reduced because of the strain distribution across the quantum dot due to the indium content of the quantum dot.

Choose a quantum dot and surround material that is strain-free. This has been shown to drastically improve the spin coherence time in the quantum dot, allowing for longer quantum memory time and larger photon entanglement. This project will construct a GaAs quantum dot instead of InAs, in a host material of AlGaAs so that no strain is produced. Metallic aluminium will be used to etch nanometre-scale hole regions in the AlGaAs layer, after which GaAs will be added to fill the holes. Once these quantum dots have been developed and characterised, optical cavities will be constructed around the quantum dots to enhance their outcoupling.