Final Report Summary - ISSIS (Integrated Single-photon Sources in Silicon) Nonlinear pair photon sources that utilise four-wave mixing can have the advantage of producing photons of a well-controlled spectrum—an essential prerequisite for the indistinguishability required to achieve the high-fidelity quantum interference and that lies at the heart of all photonic based approaches to quantum information science. Lithographically described architectures such as silicon-on-insulator waveguides increase the generation efficiency by means of their very small mode area, and enable precise dispersion engineering of emission (allowing the spectral characteristics to be tailored) which combined with their integrated nature makes them ideal for systems-integration with waveguide circuits. The fundamental facts that emission from these sources is spontaneous and uncontrollable, and they suffer from intrinsic contributions from higher-order non-linear photon states currently limit these sources to few photon-number experiments. The approach known as source multiplexing was posited in 2002 and can in principle achieve near-unit efficiency of generating pure single photons, providing a route to going far beyond the present limit of bulk optical experiments. The multiplexed approach of this programme requires the integration of heralded photon sources with optical delay lines, fast switching and control electronics, and has been broadly very successful.The principle achievements have been the demonstration of near-perfect quantum interference between on-chip photon sources, the development of stable optical delay lines, the introduction of a revolutionary switch / routing technology to the field of quantum photonics with industrial partners IBM, and the development of the electronic interfaces and systems required for high-speed feed-forward and routing. Further details are outlined in the mid-term and periodic reports.This project has been successful not only in its scientific achievements but also its outreach activities in bringing the field of quantum information science to greater society, and in its legacy of ongoing projects and applications. The packaging and chip based architectures developed in this programme have been used to create a unique teaching / educational tool call the ‘Quantum in the Cloud’. With this app’ external web-users can register to access a programmable on-line quantum optics chip and perform quantum optics experiments through a web browser. The activity is primarily intended to serve as a teaching resource for 16+ year olds and has received considerable media attention including press reports in publications such as New Scientist [No. 2934 14/09/13 “Entangled internet”] and has featured on about 20,000 news, technology and computing websites and blogs. In addition the chip based architectures that Dr Marshall has developed in this Fellowship also featured in the New Scientist article “Honey, I shrunk the quantum computer” [No. 2945 30/11/14] which outlined the scope and breadth of the impact that quantum computing is likely to have on society. Most significantly though, the work that this Marie Curie project began will continue in a number of different forms. The results from Dr Marshall’s Marie Curie IFF work formed the basis of a subsequent EPSRC Early Career Fellowship application (announcement of outcome Oct. 2014) and many related themes and ideas have featured in the successfully funded EPSRC Programme Grant “Engineered Photonic Quantum Technologies” [EP/L024020/1 value £4.8M] where the programme on multiplexed source development forms a major work-package. Finally Dr Marshall is a Co-investigator on the recently submitted University of Bristol lead EPSRC Quantum Technology Hub proposal [EP/M013502/1 value £47.5M] which builds on many of the principles Dr Marshall founded during his Marie Curie Fellowship and attempts to take photonic quantum technologies to the marketplace by virtue of the demonstration that the field can outperform classical computing approaches to problems relevant to society.
