Title: Dispersive optical detection of magnetic Feshbach resonances in ultracold gases,
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.