QSUM: Quantum Science with Ultracold Molecules

For over a century, scientists have been fascinated, and at times mystified, by quantum mechanics, the theory that governs atoms, molecules and, indeed, all matter at a microscopic level. Central to this theory are two concepts: (1) Wave-particle duality - the idea that particles, such as electrons in an atom, can behave like waves and that light waves can behave like particles, and (2) entanglement - the concept that once two (or more) particles have interacted, they cannot be treated as independent entities no matter how far apart they are. These inherently quantum phenomena are at the heart of a wide range of physical effects, but their role is often extremely difficult to elucidate. For example, in solid materials, where every atom interacts with many other atoms, it is very challenging to predict and understand how the quantum behaviour will manifest itself, and yet it leads to effects, such as high-temperature superconductivity and special forms of magnetism. Our Programme will advance the understanding of these complex quantum systems by studying the behaviour of molecules cooled to very low temperatures where we can isolate their quantum behaviour. In this respect, the use of molecules is crucial. Their rich internal structure means they couple strongly to electric and microwave fields, and interact with each other over a much greater distance compared with atoms. In advancing our understanding of the quantum science of molecules, we will also learn how to harness their properties to build new devices, including sensors of exceptional sensitivity, computers capable of solving previously unsolvable problems, and simulators that can design new materials, magnets and superconductors.

To study the quantum science of molecules in a controlled and systematic way, we need to develop the ability to manipulate the quantum properties of individual molecules. The first step towards this goal is to remove the thermal motion that normally hides their quantum behaviour. We have already developed methods to achieve this both using molecules in the solid state and in the gas-phase. In the solid state, we have demonstrated that certain organic dye molecules, when embedded in a suitable solid cooled to cryogenic temperatures, behave as near-ideal two-level quantum systems. Such molecules have the perfect properties to act as interfaces between quantum light and quantum matter - an essential building block of many future quantum devices. We will learn how to exploit these properties to generate single photons on demand, control individual photons, and store quantum information. In the gas phase, we have extended the methods of laser cooling and developed new techniques to cool molecules to within a millionth of a degree above absolute zero. In this quantum regime, it is possible to exert complete control over the internal state and motion of the molecules. With this control we can learn how to couple molecules to microwave and optical waveguides, to trap molecules on chips, to assemble ordered arrays of molecules that replicate the crystalline structure of real materials, and to explore how the interactions between molecules govern the behaviour of the many-particle system.

These ambitious goals calls for radical advances, which we will deliver through a set of interconnected experiments intimately linked to state-of-the-art theory. With isolated molecules we will develop the control of single molecules and their coupling to single photons; with small arrays of interacting molecules we will control interactions and entanglement in simple geometries; and with two- and three-dimensional lattices we will understand the complex behaviour of strongly interacting many-particle systems. Through these projects, our Programme will lay the foundations for a broad range of future scientific advances and technological applications based on the quantum control of molecules.

QSUM will address fundamental questions in quantum science. The primary impacts will be new knowledge, new capability, the training of people, and improved public engagement. The stimulus we provide to new quantum technologies will benefit the economy and society in the longer term.

Knowledge:
We will learn how to use molecules to build and control strongly interacting many-body quantum systems, and how to handle and exploit complexity in such systems. We will learn to entangle molecules and explore their applications in quantum information processing. We will couple molecules to nanophotonic and microwave circuits and study how this capability might be used to make devices. The scientific knowledge and new techniques we generate will feed into a chain of research and development leading to new capability and technology across a range of disciplines, including condensed-matter physics, quantum technology and metrology. Our work will impact on two of the "Physics Grand Challenges" identified by EPSRC, namely "Emergence and Physics Far From Equilibrium" and "Quantum Physics for New Quantum Technologies".

People:
Our programme spans disciplines from quantum optics to condensed matter to chemistry, couples experiment and theory, and unites world-leading researchers in a truly collaborative effort. We will attract exceptional researchers, who will develop cutting-edge methods of quantum science and the capacity to become future leaders in Quantum Science and Technology. The postgraduate and postdoctoral researchers involved in this research will acquire expertise in electronics, numerical modelling, data analysis, laser science, optics, imaging, device physics, microwave engineering, software development, and statistics. These are all areas of importance for the UK economy and we expect to supply people to high-tech industry and numerically intensive commercial sectors, such as, finance, software modelling and consultancy.

Economy & Society:
In the short term, we expect to drive advances in high-tech equipment which can be exploited by UK manufacturers, because our research often requires us to extend the capabilities of commercially available equipment and to develop new devices.
In the long term, quantum science with molecules has the potential to generate a new wave of quantum technologies with social and economic benefits. Molecular sensors offer enhanced sensitivity to electric and microwave fields with applications in surface science, field calibration and the detection of weak signals. Molecules coupled to microwave and photonic circuits will provide single photons on demand to quantum networks, and be used as quantum non-demolition photon detectors and memories. Quantum simulation with molecules will address important problems in many-body physics, such as understanding high-temperature superconductors, and will aid the design of new materials and devices. Through our Advisory Group and links with the UK academic community we will engage with the UK National Quantum Technology Programme to identify promising technological applications of our research at an early stage.

Public engagement:
Our outreach activities will help ensure that the public is fully engaged with science and recognises its importance to society. We will present simple explanations of our work to schools and the wider community, and will work with a recognised artist to develop innovative approaches to communicating the subtleties of quantum science to a general audience. We will also promote our research to policy-makers in the UK and at the European level to help maintain the support of physical sciences research.