Scaleable integration of electronic and Photonic integrated circuits for quantum optics in silicon

The majority of this PhD will be undertaken with Josh in The Big Photon group looking at scalable integration of electronic and photonic integrated circuits for quantum optics in silicon. Another project will be undertaken with Jorge looking at frequency multiplexed control of phase modulators in order to reduce wiring requirements into the cryostat and onto the chip. These projects fall under the same banner of scalability in silicon photonics with both supervisors eager to collaborate.

Photonic integrated circuits (PICs) represent a promising platform for classical and quantum information processing. Information can be encoded into different properties of the light confined to waveguides lithographically fabricated on the PICs. Manipulation of the light, and thus the encoded information, is typically achieved using beam splitters and phase modulators. Reck et al. showed that any NxNunitary operation can be expressed as some linear combination of 2x2 unitary operations achieved using simple Mach-Zehnder Interferometers. These Reck schemes, and other large-scale manipulation of quantum states on chip, will require>1000 phase modulators thus be requiring a number of electrical control wires of the same order. To reduce this wiring bottleneck multiplexing techniques can be used to allow for the control of multiple phase modulators from a single, or few, control wires. Designing the phase modulators to be frequency dependent would allow for all modulators to be controlled froma single control wire with the phase modulating voltages superimposed. This scheme would allow for simultaneous and independent control of all modulators. This scheme is of particular importance for photonic systems operating at cryogenic temperatures where the cooling system imposes strict limitations on the number of control wires available. Many quantum optic schemes in silicon photonics are non-deterministic and require the use of feed-forward signals to correctly route heralded events. Single-photons in silicon photonics are generated through parametric processes that are non-deterministic, requiring the heralding of the idler photon through detection of the signal photon. Additionally, in order to reduce the chances of undesired multi-photon generation events the pump power is reduced, further reducing the likelihood of photon-pair production. In order to achieve pseudo-deterministic production of heralded single-photons multiple sources are multiplexed together such that a successful single-photon generation even at one source can be switched to the output. When completely integrated on chip, the short time available for switching the single-photon requires highly integrated and fast electronics. Design of this electronics architecture and the way in which it is integrated in a scalable manner requires additional research.

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.