Magneto-optical trapping and sympathetic cooling of molecules

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In a magneto-optical trap (MOT), a combination of precisely-tuned laser light and a magnetic field is used to cool atoms to temperatures below 1 milli-Kelvin and trap them for minutes at a time. For over 25 years the MOT has been at the heart of all applications that use ultracold atoms. These include state-of-the-art instruments such as atomic clocks, magnetometers, gravimeters and accelerometers, measurements of constants, and a wide range of studies into the properties and behaviour of matter in the quantum regime. The potential applications of ultracold molecules go even further. They can be used as sensitive field sensors, and for making extremely precise measurements that test our most fundamental models of physics. Because molecules interact more strongly than atoms they can be used to study how quantum matter behaves when every particle is interacting with every other. This is important for understanding and designing new materials and chemical processes. Ultracold molecules can also be used to study fundamental processes in chemistry at the quantum level, and to make components of a quantum processor. To realize these applications, we first need to learn how to make a MOT for molecules. This is more difficult than for atoms because the laser light tends to set molecules rotating and vibrating, heating them up instead of cooling them down. Our previous work has shown how to overcome these difficulties, and we are now ready to make the MOT, which is the main subject of this proposal.We will focus on calcium fluoride (CaF) molecules. These will be slowed to rest and then captured in the MOT where multiple laser frequencies will be used to cool and trap them. Our simulations show that the CaF will cool to about 1 milli-Kelvin. This is an excellent starting point for many applications, but still not cold enough for others. To reach even colder temperatures, the CaF will be mixed with Rb atoms which are easy to cool to micro-Kelvin temperatures. We will investigate the collisions between these two species in a magnetic field and in a microwave field. Under optimum conditions, the CaF will thermalize with the Rb, allowing us to reduce their temperature to about 1 micro-Kelvin.