Quantum Many-Body Physics with Ultracold Polar Molecules

One of the greatest challenges in modern physics is to understand the behaviour of interacting many-body quantum systems. Such systems are important in condensed-matter physics, nuclear and particle physics, cosmology, chemistry and biology. In many cases they are poorly understood because they are too complex to simulate on classical devices and the systems found in nature are difficult to control on a particle-by-particle basis. This has prompted the development of quantum simulators as an alternative route to understanding many-body quantum phenomena.
Our vision is to use ensembles of ultracold polar molecules to explore the physics of many-body quantum systems and understand the emergent phenomena they exhibit. Our approach exploits the long-range anisotropic dipolar interactions and rich internal structure of diatomic molecules, combined with the exquisite control of ultracold platforms. Every element of the systems we study will be under our control – the quantum states of the molecules, the sign and strength of their interactions, their mobility in each spatial dimension, the number of internal states involved, the degree of disorder, and their coupling to the environment. This level of control and versatility is unique, allowing us to access parameter regimes that are not attainable in other systems.
We have devised a programme that spans multiple quantum platforms and a wide range of interconnected many-body phenomena. We will use small ensembles of individually controlled molecules held in optical tweezers where the geometry of the array and the states of individual molecules are controlled dynamically.  We will also use larger ensembles in optical lattices where the interactions are stronger and there is controlled tunnelling between sites, leading to more complex many-body phenomena. We will address and detect individual molecules in lattices using quantum-gas microscopy to reveal further details of the behaviour of the system. We will exploit the long-lived rotational and hyperfine states of our molecules to encode interacting pseudo-spins and to engineer synthetic lattices. Finally, we will create molecular Bose-Einstein condensates with strong dipolar interactions and explore their rich properties. The synergies between these research strands and experimental platforms will be fundamental to accelerating progress and mitigating risk, allowing us to cement the UK's leading position in this field.
We will collaborate at the interface between few-body physics, many-body physics, molecular quantum gases, quantum simulation and precision measurement to reveal how new phenomena emerge in ensembles of interacting quantum particles. By bringing together our expertise from across these fields, we will make transformative advances that we could never make alone. We will connect the few-body theory needed to understand the microscopic interactions of our molecules with the many-body theory needed to understand the emergent properties. We will engineer and quantify the entanglement that is central to all many-body quantum phenomena, study the behaviour of strongly interacting quantum fluids, explore spin dynamics, quantum magnetism and the exotic phases that emerge when spins tunnel between sites of a lattice, and use synthetic lattices to extend our exploration into new territories. We will harness the strongly correlated many-body phases of molecules to demonstrate quantum-enhanced sensors with future applications in quantum technologies and tests of fundamental physics. Our work will challenge state-of-the-art theoretical methods and cast light on the physics of many-body phenomena in other settings. As such, our arrays of polar molecules will be powerful and versatile platforms for simulating many-body quantum systems.