Efficient sources and strong filters for silicon quantum photonics in the mid-infrared

Lead Research Organisation: University of Bristol
Department Name: Physics


At wavelengths near the two-photon band edge of silicon (2.1um) quantum information processing applications benefit from many desirable properties. Here, silicon exhibits a minimum in the two-photon absorption rate and a maximum in the nonlinear refraction, making this band ideal for low-loss nonlinear silicon photonics. Specifically, these properties are desired in the design of photon pair sources utilising spontaneous four wave mixing (SFWM). Photon pair sources underpin many quantum technologies in computation, communications and sensing and so the development of bright, high purity, indistinguishable and high heralding efficiency photon sources is crucial. SFWM based sources are powered by an intense pump laser which must be subsequently separated from the single photon products, with suppression needed right down to the single photon level (-130dB). This project will attack this problem from above-by making SFWM sources more efficient-and from below-by making pump-rejection filters better. The use of photonic crystal cavities as photon-pair sources will be explored to produce high-quality photons with relatively low pump powers. These source designs will be combined with fresh ideas on high-extinction-ratio filters for pump rejection, integrated on-chip, and with on-chip filtering of blackbody background. These filters will be both spectral and spatial in nature. These developments will open new applications relying on the integration of heralded photon-pair sources on silicon chips.

Planned Impact

Our ambitions for the impact of the Quantum Engineering CDT are simple and clear: our PhD graduates will be the key talent that creates a new, thriving, globally-competitive quantum industry within the UK. In Bristol we will provide an entire ecosystem for innovation in quantum technologies (QT). Our strong and diverse research base includes strengths going from quantum foundations to algorithms, experimental quantum science to quantum hardware. What makes Bristol unique is our strong innovation and entrepreneurship focus that is deeply embedded in the entire culture of the CDT and beyond. This is reflected in our recent successful venture QTEC, the Quantum Technologies Enterprise Centre, and our Quantum Technologies Innovation Centre (QTIC), which are already enabling industry and entrepreneurs to set up their own QT activities in Bristol. This all occurs alongside internationally recognised incubators/accelerators SetSquared, EngineShed, and UnitDX.

At the centre of this ecosystem lies the CDT. We will not just be supplying existing industry with deeply trained talent, but they will become the CEOs and CTOs of new QT companies. We are already well along this path: 7 Bristol PhD students are currently involved in QT start-ups and 3 alumni have founded their own companies. We expect this number to rise significantly when the first CDT cohort graduates next year (2 students have already secured start-up positions). Equally, it is likely that our graduates will be the first quantum engineers to make new innovations in existing classical technology companies - this is an important aspect, as e.g. the existing photonics, aerospace and telecommunications industries will also need QT experts.

The portfolio of talent with which each CDT graduate will be equipped makes them uniquely suited to many roles in this future QT space. They will have a deep knowledge of their subject, having produced world-leading research, but will also understand how to turn basic science into a product. They will have worked with individuals in their cohort with very different skills background, making them invaluable to companies in the future who need these interdisciplinary team skills to bring about quantum innovations in their own companies. Such skills in teamworking, project management, and self-lead innovation are evidenced by the hugely successful Quantum Innovation Lab (QIL). The idea and development of QIL is entirely student-driven: it brings together diverse industrial partners such as Deutsche Bank, Hitachi, and MSquared Lasers, Airbus, BT, and Leonardo - the competition to take part in QIL shows the hunger by national industry for QT in general, and our students' skills and abilities specifically. With this in mind, our Programme has been co-developed with local, UK, and international companies which are presently investing in QT, such as Airbus, BT, Google, Heilbronn, Hitachi, HPE, IDQuantique, Keysight, Microsoft, Oxford Instruments, and Rigetti. The technologies we target should lead to products in the short and medium term, not just the longer term. The first UK-wide fibre-based quantum communication network will likely involve an academic-industrial partnership with our CDT graduates leading the way. Quantum sensing devices are likely to be the product of individual innovators within the CDT and supported by QTIC in the form of spin-outs. Our graduates will be well-positioned to contribute to the advancement of quantum simulation and computing hardware, as developed by e.g. our partners Google, Microsoft and Rigetti. New to the CDT will be enhanced training in quantum software: this is an area where the UK has a strong chance to play a key role. Our CDT graduates will be able to contribute to all aspects of the software stack required for first-generation quantum computers and simulators, the potential impact of which is shown by the current flurry of global activity in this area.


10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023607/1 01/09/2019 29/02/2028
2266060 Studentship EP/S023607/1 23/09/2019 22/09/2023 Quinn Palmer