Creating ultra-cold molecules by sympathetic cooling

Laser cooling has been of primary importance in the exploration of ultra-cold interactions between trapped atoms, for quantum atom optics, and for precision metrology through high-resolution spectroscopy. It has also provided a well-controlled testing ground for condensed matter physics, and more recently quantum information. Attention has now turned to molecules because of the quite different interactions that can occur between ultra-cold molecules. They are seen as ideal candidates in the search for CPT violation, for exploring ultra-cold chemistry, and for the creation of novel quantum fluids using dipolar molecules. Unfortunately, laser cooling, which has been so successful for many atomic species cannot be applied to molecules and thus new methods are required to reach this new regime in molecular and ultra-cold physics. This proposal aims address this problem by utilising the very general techniques of sympathetic and evaporative cooling to create ultra-cold molecules from cold stationary molecules that have been created by optical Stark deceleration. To undertake this work we will bring ultra-cold laser cooled xenon atoms into thermal contact with stationary cold molecules initially at temperatures in the 10 mK to 1 K range. We will use elastic collisions between the cold xenon atoms and the molecules co-trapped within an optical field to thermalise the mixture, bringing it to a common temperature below the 1 mK bottleneck that currently exists. Although in principle sympathetic and evaporative cooling are applicable to many molecular species, this project will explore the cooling of molecular hydrogen and benzene by collisions with ultra cold xenon, producing molecules in the 100 microkelivn temperature range and below. An important part of this programme will be the study, via experiment and theory, the atom-molecule collisions that are vitally important for sympathetic and evaporative cooling, as well as for the potential ultra-cold molecular chemistry that can be studied once the molecules are cooled into the microkelvin temperature regime. This research will utilise our optical Stark decelerator and will build a magneto-optical trap for producing ultra-cold xenon atoms. We will also build a deep optical trap that will be capable of holding atomic or molecular species for the long periods (seconds) required for thermalisation.