Dispersive optical detection of magnetic Feshbach resonances in ultracold gases
  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.
