Production of ultracold ${\mathrm{Cs}}^{*}\mathrm{Yb}$ molecules by photoassociation

We report the production of ultracold heteronuclear ${\mathrm{Cs}}^{*}\mathrm{Yb}$ molecules through one-photon photoassociation applied to an ultracold atomic mixture of Cs and Yb confined in an optical dipole trap. We use trap-loss spectroscopy to detect molecular states below the $\mathrm{Cs}\left({}^{2}P_{1/2}\right)+\mathrm{Yb}\left({}^{1}S_0\right)$ asymptote. For ${}^{133}\mathrm{Cs}{}^{174}\mathrm{Yb}$, we observe 13 rovibrational states with binding energies up to $\sim 500\mathrm{GHz}$. For each rovibrational state we observe two resonances associated with the Cs hyperfine structure and show that the hyperfine splitting in the diatomic molecule decreases for more deeply bound states. In addition, we produce ultracold fermionic ${}^{133}\mathrm{Cs}{}^{173}\mathrm{Yb}$ and bosonic ${}^{133}\mathrm{Cs}{}^{172}\mathrm{Yb}$ and ${}^{133}\mathrm{Cs}{}^{170}\mathrm{Yb}$ molecules. From mass scaling, we determine the number of vibrational levels supported by the 2(1/2) excited-state potential to be 154 or 155.

Figure 1

One-photon photoassociation. When $\hslash {\omega }_1=E_v$ ($\hslash {\mathrm{\Delta }}_{\mathrm{FB}}=0$) a pair of colliding ground-state Cs and Yb atoms are associated to form a CsYb molecule in a rovibrational level of the electronically excited 2(1/2) molecular potential. The molecular curves plotted here are adapted from Ref. [53]. The hyperfine splitting shown on the right is not to scale.

Figure 2

Modification of ${\mathrm{Cs}}_2$ photoassociation rate using a Feshbach resonance. The left panel shows ${\mathrm{Cs}}_2$ photoassociation rates as a function of detuning from the $0_u^{+}v=136$ line for varying magnetic field strengths. The right panel shows the Cs scattering length as a function of magnetic field [62]. For clarity, narrow Feshbach resonances at $14.4\mathrm{G}$, $15.1\mathrm{G}$, and $19.9\mathrm{G}$ are not shown. The red circles show the scattering lengths at magnetic fields corresponding to the measurements on the left.

Figure 3

Observation of the photoassociation resonance for $n^{\prime }=-11$ of $\stackrel{*}{{}^{133}\mathrm{Cs}}{}^{174}\mathrm{Yb}$. Relative number of Cs atoms remaining after a 300 ms pulse of PA light versus detuning from the $F^{\prime }=4$ line (${\mathrm{\Delta }}_{\mathrm{FB}}$). The green (red) trace shows the photoassociation spectrum of Cs with (without) Yb in the dipole trap. The red trace is offset for clarity. The statistical error in the atom number is shown by the error bars on the right-hand side. The dashed green lines shows the centers of the CsYb PA resonance for the two hyperfine components.

Figure 4

Measured hyperfine splitting as a function of the effective internuclear distance, $R_{\mathrm{eff}}$; see text for details. The horizontal dashed line shows the Cs atomic hyperfine splitting of the $m_F=+3$ levels in the $6P_{1/2}$ state at a magnetic field of $2.2\left(2\right)\mathrm{G}$ [77, 78]. The solid line is an exponential fit.

Figure 5

Binding energies of vibrational levels of ${}^{133}\mathrm{Cs}{}^{174}\mathrm{Yb}$ in the 2(1/2) excited state. Top: The binding energies as a function of the vibrational quantum number counted from dissociation, $n^{\prime }$. The solid green line shows a fit to the data using the extended Le Roy–Bernstein equation. The lower two panels compare the residuals for the fits using the standard and extended Le Roy–Bernstein equations. The error bars are much smaller than the data points.