Magnetic field modification of ultracold molecule-molecule collisions

TL;DR

This study provides a detailed quantum mechanical analysis of ultracold molecule-molecule collisions under magnetic fields, revealing efficient spin relaxation, dense Feshbach resonances, and the potential for tuning scattering properties in ultracold gases.

Contribution

It offers the first comprehensive quantum calculations of magnetic field effects on ultracold molecule-molecule collisions, highlighting the role of Feshbach resonances and spin state dependence.

Findings

Magnetic spin relaxation is highly efficient above 1 mT.

Feshbach resonances occur at a density of ~100 per Tesla in the ground state.

Scattering length can be widely tuned using magnetic fields.

Abstract

We present an accurate quantum mechanical study of molecule-molecule collisions in the presence of a magnetic field. The work focusses on the analysis of elastic scattering and spin relaxation in collisions of O2(3Sigma_g) molecules at cold (~0.1 K) and ultracold (~10^{-6} K) temperatures. Our calculations show that magnetic spin relaxation in molecule-molecule collisions is extremely efficient except at magnetic fields below 1 mT. The rate constant for spin relaxation at T=0.1 K and a magnetic field of 0.1 T is found to be as large as 6.1 x 10^{-11} cm3/s. The magnetic field dependence of elastic and inelastic scattering cross sections at ultracold temperatures is dominated by a manifold of Feshbach resonances with the density of ~100 resonances per Tesla for collisions of molecules in the absolute ground state. This suggests that the scattering length of ultracold molecules in the absolute ground state can be effectively tuned in a very wide range of magnetic fields. Our calculations demonstrate that the number and properties of the magnetic Feshbach resonances are dramatically different for molecules in the absolute ground and excited spin states. The density of Feshbach resonances for molecule-molecule scattering in the low-field-seeking Zeeman state is reduced by a factor of 10.