We use photoassociation of spin polarized ($F=3$, $m_f=3$), ultracold cesium atoms confined in a 1D optical lattice to confirm the existence of the two lowest lying vibrational levels in the $0^-_g$ pure long-range molecular potential of Cs$_2$. The observation of these two levels confirms the theoretical predictions of Bouloufa et al.  postulating that the numbering of vibrational levels of this potential needs to be shifted by two in order to agree theory with experimental data. We also provide unambiguous evidence that the work of Zhang et al.  which claimed priority of observing these new levels, in fact observed levels belonging to the $0^+_u$ molecular potential.
Due to the expected low molecular formation rate we have implemented Feshbach resonance-enhanced association of molecules in $v = 0$ and $v = 1$. Several of such resonances are present at fields below 70 G but the newly discovered vibrational levels could be detected only in the vicinity of the Feshbach resonance at 19.9 G .
We have determined the binding energies of the ($v$,$J$) = $(0,2)$, $(1,0)$, $(1,2)$ and $(1,4)$ with absolute accuracy better than 1 MHz by referencing the photoassociation laser to a frequency comb. For the $v = 1$ level we have extracted the rotational constant of ~56 MHz.
 Bouloufa, N., Crubellier, A., & Dulieu, O. Phys. Rev. A, 75(5), 052501(2007)
 Zhang, Y., Ma, J., Wu, J., Wang, L., Xiao, L., & Jia, S. . Phys. Rev. A, 87(3), 030503(2013)
 Tolra, B. Laburthe, et al. EPL (Europhysics Letters) 64.2 (2003): 171
|Presenter name||Mariusz Semczuk|
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