MMQA: MicroKelvin Molecules in a Quantum Array

All matter is governed by quantum physics. Even in bulk material, with huge numbers of particles, many important quantum phenomena persist. When the particles only interact appreciably with their nearest neighbours, it is usually possible to understand the bulk behaviour in terms of the quantum physics of the constituents. Often however, the interactions are long-range and strong, meaning that every particle interacts appreciably with every other particle. The behaviour of the bulk cannot then be understood from that of the constituents, and from a theoretical point of view the system is usually unsolvable. From such strongly interacting quantum systems emerge extraordinary and fascinating phenomena that are not at all well understood, such as high temperature superconductivity and exotic forms of magnetism.Modelling such a complex system on a computer is an impossible task. Instead, we need a physical model of strongly interacting quantum particles where the interactions can be controlled. We plan to build an instrument that cools polar molecules to microKelvin temperatures and below, arranges them in a regular array, and controls their motion, their orientation, and the way they interact. This instrument will be used as a quantum simulator - an ideal, tuneable and highly versatile tool for modelling strongly-interacting quantum systems and understanding the remarkable quantum phenomena they exhibit. This same device could also be used for quantum information processing, or as a multi-particle interferometer for making extremely sensitive measurements of electric, magnetic, gravitational and exotic forces.The use of ultracold polar molecules is crucial for realising this vision. Unlike atoms, the molecules have strong, tuneable, long-range interactions, an essential ingredient for the quantum simulator. While the techniques for cooling atoms to microKelvin temperatures are well established, methods to do the same for molecules are only now emerging. A large part of our programme focuses on developing these methods. We will follow two main routes. One is to start with trapped ultracold atoms, which are then paired up to form weakly-bound ultracold molecules. We will need to transfer them to deeply bound states without heating them up, using a sequence of carefully tailored laser pulses. In the second approach, a beam of molecules from a cryogenic source is decelerated to rest and trapped using electric, magnetic or optical forces. These molecules will be far too hot to form the quantum gas we need, but they could be brought to this regime by sympathetic cooling using ultracold atoms as a refrigerant. The final quantum array will be made by loading our ultracold molecules into a trap formed by laser beams. The configuration of the beams - orientation, polarisation and frequency - allows the quantum evolution to be studied for a wide variety of potentials. Low-frequency external electric fields will be used to control the interactions between molecules.The advances we make will also stimulate new and diverse areas of research: (i) Molecules allows one to test the fundamental symmetries of space and time through measurements of particle dipole moments and the constancy of molecular frequencies. (ii) We will study the collisions of molecules at temperatures where quantum reflection, tunnelling and Bose/Fermi statistics are all important. (iii) Polar molecules can interact with nano-mechanical structures through the long-range dipole interaction, allowing quantum states to be mapped from one to the other. The production of dense samples of ultracold molecules is the key step towards these goals.It will be a major milestone in quantum physics to demonstrate the molecular array. We bring together researchers from Physics and Chemistry at Durham and Imperial, each contributing the highest UK expertise on a key part of our joint programme, to tackle all the experimental and theoretical problems in a unified way.

Our research programme will have an impact on society and the economy both in the short term, and in the long term. 1. Immediate impact We see four ways in which industry, the wider community and schools will benefit from our programme in the short term. (i) Supply of highly trained personnel to high-tech industry. High-tech industries require professionals with exceptional levels of technical skill. Through this programme our postgraduate and postdoctoral researchers will acquire expertise in vacuum science, 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 that will be enhanced by our trainees. We expect about half of them to move into industry and other high-tech spheres such as finance and consultancy. (ii) Driving advances in high-tech equipment. Our research often requires us to extend the capabilities of commercially available equipment and sometimes to develop fundamentally new equipment. In some cases we have driven improvements to commercial equipment through consultation with manufacturers who then exploit these advances commercially. (iii) Presentation of our programme to the wider community. The wider community will benefit from our efforts to explain in a simple way what we do and why it is important. This will contribute to the growing effort, in the UK and globally, to ensure that the public is fully engaged with science and recognises its enormous importance in the economy and society. We will also promote the science in our research to policy-makers in the UK and at the European level. (iv) Outreach to schools. School pupils and teachers will benefit from the outreach activities that we will initiate. They will benefit from their contact with researchers at the cutting edge of an exciting field, who will have received high quality training in outreach work. They will also benefit from the opportunity of visiting our laboratories, which they always find inspiring and stimulating. 2. Long term impact It will take time, probably a decade or more, for the benefits of our work to reach beyond the academic community. However, on this time scale the benefits may be very great. We can identify some of them already. (i) Simulating many-body quantum physics. It is widely recognised that controlled quantum interference and entanglement in practical devices is going to be important in future technology. Our molecular array will be able to simulate important unsolved problems in the quantum physics of strongly interacting systems. This will lead to better understanding of devices that exploit many-body quantum phases, such as high-temperature superconductors and Josephson junctions. Deeper understanding of these important systems will help to enhance the competitiveness of the UK economy in the emerging area of quantum technology. (ii) Precision measurement & sensing. The device we build will be an exquisitely sensitive probe of electric, magnetic and inertial forces. In the medium term, this will be used to improve understanding of fundamental forces and symmetries of nature. In the longer term, it may have practical applications in surface science, mineral detection, navigation and metrology, all areas of importance to the UK economy. (iii) Quantum information processing. QIP is already important for secure communication in the military, government agencies, and the financial sector. Over the next 10-20 years the sophistication of quantum protocols will need to increase and our device offers that potential.