Fast reprogrammable photonic experiments for quantum foundational studies

My PhD project will study quantum foundations using a hybrid approach of both experiment and theory. The aim is to work on foundational studies, whilst considering applications to quantum technologies, thus working on the overlap between these fields. I will focus on fast reprogrammable integrated photonics for use in quantum foundations experiments. I will also do theoretical work, some of which will be closely linked to experimental but also some
stand-alone theory projects. One of the areas in quantum foundations that I will be looking at is quantum causality. In quantum mechanics, the causal relations between events can have an uncertainty in a similar way to other physical properties of a quantum system, resulting in an indefinite casual order [1]. This could have a significant impact on our understanding of the notion of time, but it could also be utilised in quantum technology. For example, a potential
computational advantage from using a quantum superposition of qubit gate orders has been demonstrated [2]. Possible applications to quantum metrology [3] and communications [4] have also been investigated. Processes with indefinite causal order have been demonstrated experimentally [5], but superpositions of more complex processes will need to be created for technological applications. The first project I will work on is a direct extension of my project B, which is a chip experiment on higher order quantum causal structures, i.e., more parties and more permutations of order than any experimentally achieved so far. I will finish off characterising chip components, design the PCB, and then carry out the experiment. This will likely take up my first year. Another project we have planned is an experiment on reversing unknown unitaries. The evolution of a quantum system described by a unitary operation is in principle
reversible, but this is only possible if the unitary is known. However, we often do not have a complete description of a physical system in order to determine this unitary. Being able to reverse a unitary operation without the need to fully understand the system would be useful for studying irreversibility in quantum mechanics, and for practical applications such as removing noise by reversing unwanted evolutions of a system. Protocols for reversing unitaries have been investigated, I will work on how such protocols can be implemented experimentally. The project will involve designing a chip, having it manufactured, and then carrying out the experiment. Finally, I also plan to do a theoretical project on the energy consumption of quantum computing. This area has gained a lot of interest recently, with the need to consider the potential negative impacts and resource costs of quantum computing [6]. It requires understanding the quantum thermodynamics of quantum computation operations, and how this relates to the energy consumption of macroscopic components. This could also include studying possible fundamental limits on energy consumption at the quantum level.

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.