# Study of loss dynamics of strontium in a magneto-optical trap

## TL;DR

This paper measures the collision cross section between strontium atoms and nitrogen in a magneto-optical trap, and analyzes how these collisions affect atomic losses and frequency shifts in optical atomic clocks.

## Contribution

It provides the first experimental measurement of the Sr-N2 collision cross section and links it to the C6 coefficient, improving understanding of loss mechanisms in Sr optical clocks.

## Key findings

- Collision cross section: 8.1(4)×10^{-18} m^2
- Dominant loss mechanism: temperature-induced atomic losses
- Estimated impact on clock frequency shift

## Abstract

Collisions with background atoms are known to induce a significant shift in the frequency of state-of-the-art optical atomic clocks and contribute to state decoherence in cold atom experiments. The effects of these collisions can be quantified by measuring their cross sections. We experimentally measured the collision cross section between $^{88}$Sr$-$N$_{2}$ in a Magneto-Optical Trap (MOT). The measurement was carried out by monitoring the atom number loss rate as a function of background pressure of N$_{2}$ and the cross section thus obtained was 8.1(4)$\times 10^{-18}$ m$^{2}$. The measured collision cross section has been utilized for the determination of C$_{6}$ coefficient of the ground state (${^1S}_0$) of $^{88}$Sr atom, which can be useful to estimate the relative frequency shift in the clock transition. We also estimate the loss rate induced by the combined effect of the decay of atoms in the long-lived ${^3P}_0$ state and temperature-induced atomic losses from the capture volume of the MOT. We find that the contribution due to the latter is dominant in comparison to the other atomic loss channels and must be included in the studies that rely on the total loss rate measurement.