# Multichannel interactions of two atoms in an optical tweezer

## TL;DR

This paper investigates Na-Cs atom interactions in an optical tweezer using multichannel quantum defect theory, measuring scattering lengths and Feshbach resonances, advancing understanding of complex atomic interactions.

## Contribution

It introduces a methodology combining optical tweezer experiments with MQDT to characterize multichannel atomic interactions, including Feshbach resonances.

## Key findings

- Measured triplet and singlet scattering lengths via Raman spectroscopy.
- Observed magnetic Feshbach resonances consistent with MQDT predictions.
- Demonstrated the effectiveness of optical tweezer-based measurements for complex interactions.

## Abstract

The multichannel Na-Cs interactions are characterized by a series of measurements using two atoms in an optical tweezer, along with a multichannel quantum defect theory (MQDT). The triplet and singlet scattering lengths are measured by performing Raman spectroscopy of the Na-Cs motional states and least-bound molecular state in the tweezer. Magnetic Feshbach resonances are observed for only two atoms at fields which agree well with the MQDT. Our methodology, which promotes the idea of an effective theory of interaction, can be a key step towards the understanding and the description of more complex interactions. The tweezer-based measurements in particular will be an important tool for atom-molecule and molecule-molecule interactions, where high densities are experimentally challenging and where the interactions can be dominated by intra-species processes.