Observation of blue-shifted ultralong-range Cs${}_2$ Rydberg molecules

We observe ultralong-range blue-shifted Cs${}_2$ molecular states near $n{s}_{1\mathrm{/}2}$ Rydberg states in an optical dipole trap, where $31\le n\le 34$. The accidental near degeneracy of $(n-4)l$ and $ns$ Rydberg states for $l>2$ in Cs, due to the small fractional $ns$ quantum defect, leads to non-adiabatic coupling among these states, producing potential wells above the $ns$ thresholds. Two important consequences of admixing high angular momentum states with $ns$ states are the formation of large permanent dipole moments, $\sim 15-100,$Debye, and accessibility of these states via two-photon association. The observed states are in excellent agreement with theory. Both projections of the total angular momentum on the internuclear axis are visible in the experiment.