Sensitive detection of cold cesium molecules formed on Feshbach resonances

We observe the dynamic formation of quasibound Cs2 molecules near Feshbach resonances in a cold sample of atomic cesium. Using an external probe beam, more than 15 weakly coupled molecular states are detected with high sensitivity, whose collisional formation cross sections are as small as σ=2x10-16 cm2. By modeling the molecule formation and dissociation processes with rate equations, we conclude that at an atomic density of 1013 cm-3 and temperature of 5 μK, more than 5(1)x105 Cs2 molecules in a single rovibrational state coexist with 108 Cs atoms in our trap