This project aims to use photonic quantum simulators to investigate key open questions in particle physics involving, separately, neutrinos and mesons. The project will tackle the existence of 'sterile' flavours of neutrino, how flavour oscillations are modified by neutrino interactions, and neutral B-meson oscillations (between themselves and their antiparticle) that violate CP symmetry by a greater degree than allowed by the Standard Model. Photonics is a versatile platform for simulating fermionic and anyonic statistics, and non-Hermitian Hamiltonians. Quantum photonics experiments have progressed to the point where >100 photons can be generated, coherently manipulated, and detected. Leveraging the mature fabrication capabilities of the telecoms and microelectronics industries has allowed ~1000 optical components to be co-integrated into a single photonic quantum processor. In this project we aim to use the reconfigurability afforded by photonics to map complex systems studied in particle physics into the controllable and well understood platform of quantum photonics. Such analogue quantum simulators, where there is a one-to-one mapping between the dynamics of both systems, have been shown to be a promising avenue to useful but specific quantum computation without a fault tolerant quantum computer. Bristol University hosts an esteemed group in particle physics with longstanding links to the LHCb and CERN; the university also hosts extensive and world leading expertise and infrastructure in photonic quantum technologies. This project aims to foster interdisciplinary research, bringing the benefits of quantum computing and simulation to the high energy and particle physics community. Our ambition is for new fundamental physics to be discovered by UK particle physics researchers through modelling carried out on UK quantum computing and simulation technologies.

Computer simulations of physical models have become a vital tool in science and engineering. For example, the aerodynamics and chassis integrity for a new car design will be fully simulated on a computerised model, long before production begins, while biologists will use a simplified computer model to simulate the dynamics involved in protein folding. In both of these cases, the physics underlying the model to be simulated is that of the familiar, classical world, as is the information that is processed. In contrast, chemists working with systems at the microscopic scale (quantum chemists) must incorporate quantum physics into their physical models. But these models come up against the intractability of simulating even modestly sized quantum systems on classical computers. The number of possible configurations of any system grows exponentially with its degrees of freedom, just like the number of heads/tails configurations of a row of coins doubles with each additional coin. Since a quantum system can exist simultaneously across all of its configurations, its evolution is too large to be simulated with a classical computer. Therefore, quantum mechanical models for classical computers are necessarily limited while more compete models are fundamentally intractable to classical simulation. Yet increasingly, scientists need to understand the role of quantum physics, for example in biological molecules. The famous physicist and Nobel Laureate, Richard Feynman, identified this problem in a seminal lecture in 1982. He also proposed a solution. Feynman suggested using one controllable quantum system to simulate the model for the quantum system one wishes to study. The ultimate realisation of this ingenious concept is a digital quantum simulator that theoretically can be programmed to simulate any quantum system. Building this device is the focus of an increasingly intensive international effort, or competition. This effort is likely to be long term since isolating, digitising, and coherently controlling large quantum systems has proved to be highly challenging, due to their inclination to couple to the environment, decohere, and behave classically. After all, the world we see around us is classical, not quantum. Therefore, the road to a quantum simulator that surpasses the capabilities of classical computers seems, long and difficult, and is an ultimate goal to scientists working in quantum information science. This fellowship proposes a smart route to large-scale quantum simulations that is intrinsically scalable, and can be implemented with manufacturable technologies. The project aims to simulate quantum physical models at a scale that surpasses the capabilities of conventional computers. This is possible because a mapping has been identified between an established model for the quantum vibrational behaviour of molecules, which cannot be simulated with a conventional computer, and the description of photons in manufacturable optical chips. By injecting ensembles of single photons into a versatile optical chip, the evolution of a large molecule can be tracked. The direction of the research is to then make improvements to the molecular mathematical model with a series of perturbations, which, in loose terms, are matched by perturbations to the optical circuits in the form of weak interactions between the photons. The difficulty in getting single photons to strongly interact is the main challenge for optical quantum computers. However, developing successive generations of devices that build up layers of weak interactions allows interesting and complex simulations to be performed on an increasingly tailored and accurate molecular model. As these devices progress, they will develop additional computational capabilities, such as the calculation of factors involved in chemical transitions and characteristic properties of biotic molecules.