• Dr Mike Tarbutt
  • Dr Jony Hudson

 Laser Cooling of Molecules

Ultracold molecules are highly desirable for a diverse range of applications in physics and chemistry. These applications include precision measurements, quantum simulation and information processing, quantum chemistry, and the physics of strongly correlated quantum matter. Although laser cooling has been enormously successful in cooling certain atomic species to extremely low temperatures, the method has never been applied to molecules. For laser cooling to work, each atom/molecule needs to scatter many photons.This is only possible when the energy level structure is `closed', meaning that the cycle of absorption followed by spontaneous emission always returns the particle to its original quantum state. Molecules do not possess a closed energy structure because they are able to rotate and vibrate. A molecule, resonant with a laser, typically scatters just one, or a few, photons before decaying to a state of vibration and rotation that is not resonant with the laser.

The key to make cooling work is to find a molecule whose energy level structure is not too far from closed,and then to close it by using several laser frequencies at once. In the best cases, the set of frequencies needed can be generated using a small number of diode lasers and acousto-optic modulators and the experimental complexity, though high, is not unfeasible. This project aims to cool molecules to low temperatures using such a multi-frequency laser cooling technique.