# Dispersive optical detection of magnetic Feshbach resonances in ultracold gases

## TL;DR

This paper introduces a rapid dispersive optical method to detect and characterize magnetic Feshbach resonances in ultracold gases, significantly reducing experimental time compared to traditional atom loss spectroscopy.

## Contribution

The authors demonstrate a novel off-resonant dispersive optical technique to efficiently locate and analyze multiple Feshbach resonances in ultracold rubidium gases, including previously unobserved p-wave features.

## Key findings

- Successfully identified four Feshbach resonances in $^{87}$Rb, including two new p-wave resonances.
- Achieved resonance detection over an 18 G magnetic field range with only 21 experimental runs.
- Characterized two-body loss dynamics directly through dispersive measurements.

## Abstract

Magnetically tunable Feshbach resonances in ultracold atomic systems are chiefly identified and characterized through time consuming atom loss spectroscopy. We describe an off-resonant dispersive optical probing technique to rapidly locate Feshbach resonances and demonstrate the method by locating four resonances of $^{87}$Rb, between the $|\rm{F} = 1, \rm{m_F}=1 \rangle$ and $|\rm{F} = 2, \rm{m_F}=0 \rangle$ states. Despite the loss features being $\lesssim0.1$ G wide, we require only 21 experimental runs to explore a magnetic field range >18 G, where $1~\rm{G}=10^{-4}$ T. The resonances consist of two known s-wave features in the vicinity of 9 G and 18 G and two previously unobserved p-wave features near 5 G and 10 G. We further utilize the dispersive approach to directly characterize the two-body loss dynamics for each Feshbach resonance.