Universal Dipolar Scattering

Understanding and controlling the interactions between particles in ultracold matter constitutes one of the most important goals in quantum atom optics. Interactions are fundamental to the many body properties of an ultracold system and lead to behaviour such as superfluidity. Furthermore, there is an increasingly urgent need to understand the interactions of polar molecules as experiments rapidly progress toward the production of ultracold molecular gases. Aiming to address this need, Dr. Christopher Ticknor at the Swinburne node of ACQAO, has studied the scattering properties of ultracold polar molecules in the presence of an external electric field. The work shows that there will be limited collisional control of polar molecules, but very large scattering cross sections. The presence of the dipolar interactions dominate the scattering and prevent the particles from get close to each other where short range resonances can occur. This is in strong contrast to magnetic Feshbach resonances used in ultracold atomic systems.

Dr. Christopher Ticknor

The work further shows that when a strong dipolar system is rescaled in terms of the length and energy scale defined by the dipoles, all dipolar scattering has the same form. Thus all dipolar systems have the same scattering behavior, irrespective of the details of the scatterers. This is universal dipolar scattering. Illustrating universal dipolar scattering through numerous computational scattering calculations, the scaling behavior is extracted. Then the scaling is compared to experimental scattering data in Rydberg atoms, and there is remarkably good agreement even over many orders of magnitude. To see more about this work, see the paper Phys. Rev. Lett. 100, 133202 (2008), entitled "Collisional Control of Ground State Polar Molecules and Universal Dipolar Scattering”, or Phys Rev. A 76, 052703 (2007).

This figures shows thousands of scattering calculations transitioning from highly variable in the threshold regime to uniform as the systems enter the universal dipolar scattering regime. Once the system has reached the universal dipolar scattering regime, all the scattering behaves the same, irrespective of the conditions or the finer details of the scatterers. To illustrate this, experimental Rydberg scattering data is shown as an inset with the same scaling behavior as the molecular scattering data.