Collisional properties of cold spin-polarized nitrogen gas: theory, experiment, and prospects as a sympathetic coolant for trapped atoms and molecules

TL;DR

This study combines experiments and quantum calculations to show that cold spin-polarized nitrogen gas has slow dipolar relaxation rates, making it a promising candidate for sympathetic cooling of molecules in ultracold physics.

Contribution

It provides the first combined experimental and theoretical analysis of nitrogen's collisional properties, demonstrating its suitability for cooling applications.

Findings

Dipolar relaxation rate of ~10^{-13} cm^3/s across 1 mK to 1 K

Calculated rates are insensitive to interaction potential variations

Experimental and theoretical results are in good agreement

Abstract

We report a combined experimental and theoretical study of collision-induced dipolar relaxation in a cold spin-polarized gas of atomic nitrogen (N). We use buffer gas cooling to create trapped samples of 14N and 15N atoms with densities 5+/-2 x 10^{12} cm-3 and measure their magnetic relaxation rates at milli-Kelvin temperatures. Rigorous quantum scattering calculations based on accurate ab initio interaction potentials for the 7Sigma_u electronic state of N2 demonstrate that dipolar relaxation in N + N collisions occurs at a slow rate of ~10^{-13} cm3/s over a wide range of temperatures (1 mK to 1 K) and magnetic fields (10 mT to 2 T). The calculated dipolar relaxation rates are insensitive to small variations of the interaction potential and to the magnitude of the spin-exchange interaction, enabling the accurate calibration of the measured N atom density. We find consistency between the calculated and experimentally determined rates. Our results suggest that N atoms are promising candidates for future experiments on sympathetic cooling of molecules.