Collisions and reactions between atoms and molecules are fundamental to many parts of physics and chemistry. They control, for example, the rate at which gasses approach thermodynamic equilibrium or the production efficiency with which desired molecules can be created. In the domain of the ultra-cold, typically defined as temperatures less than 1 mK above absolute zero, quantum physics determines the "threshold" limit of these rate coefficients and classical models fail. The best atomic clocks, based on cesium and rubidium at microkelvin temperatures, are affected by these threshold collisions, while many quantum phase transition would not feasible without them.
We investigate by first-principle theoretical simulations both room-temperature and ultracold collisions of atoms and molecules. For ultracold temperatures we focus on resonant phenomena, the Fano-Feshbach resonance, controllable with external magnetic fields. These resonance have been instrumental in the observation of evidence for superfluid Cooper pairing of fermionic atoms as well as the study of Efimov trimers in bosonic atoms. Recently, it was realized that the distribution of the locations of these resonances is chaotic for highly magnetic lanthanide atoms. For room temperature collisions we focus on characterizing forward scattering processes that impart small momenta.
This research is done in collaboration with scientists at the Joint Quantum Institute (JQI), a research partnership between NIST and the University of Maryland.
Directions (in random order):
Selected Recent Publications:
K. Jachymski, M. Krych, P. S. Julienne, and Z. Idziaszek, Quantum-defect model of a reactive collision at finite temperature, Physical Review A 90, 042705 (2014).
Y. Wang, and P. S. Julienne, Universal van der Waals physics for three cold atoms near Feshbach resonances, Nature Physics 10, 768–773 (2014).
A. Petrov, E. Tiesinga, and S. Kotochigova, Anisotropy-Induced Feshbach Resonances in a Quantum Dipolar Gas of Highly Magnetic Atoms, Physical Review Letters 109, 103002 (2012).
T. M. Hanna, E. Tiesinga, W. F. Mitchell, and P. S. Julienne, Resonant control of polar molecules in individual sites of an optical lattice, Phys. Rev. A 85, 022703 (2012).