Creation and precise spectroscopy of $^{86}$Sr$_2$ halo molecules

Abstract

We report on the creation of $^{86}$Sr$_2$ molecules in the halo state and neighboring weakly bound states. Efficient molecule production via one-photon photoassociation relies on sufficient wavefunction overlap between the target vibrational states in the electronic excited- and ground-state potentials. Using Autler-Townes spectroscopy, transition strengths are measured to identify optimal pathways for production of weakly bound molecules. Vibrational splittings for the three least-bound vibrational states are measured, and dominant systematic uncertainties are evaluated with uncertainties below 100 Hz. From these splittings, absolute binding energies for these weakly bound vibrational states are determined. The results pave the way to a molecular isotope shift measurement with Sr$_2$.

Figures (6)

• Figure 1: Observation of $^{86}$Sr$_2$ molecule samples via photodissociation and subsequent absorption imaging of the resultant atomic fragments. Images are captured slightly off-axis from the optical lattice. Horizontal axis is along the direction of gravity, and both axes are in units of $\mu$m. Color bars represent optical density in arbitrary units. (a) The halo state, $v=-1$. Only the state with total angular momentum $J=0$ is bound. (b) The $v=-2$ molecules, with $J = 0$ dissociation at the center and $J = 2$ molecules receiving a greater kinetic energy and forming the outer ring; odd values of $J$ are forbidden by bosonic quantum statistics.
• Figure 2: (a) The ground-state electronic potential $X^{1}\Sigma_g^+$ asymptotes to the $^{1} S _{0}$+$^{1} S _{0}$ atomic threshold, and the excited-state potentials $1_{u}$ and $0_{u}^{+}$ asymptote to the $^{1} S _{0}$+$^{3} P _{1}$ intercombination threshold. The weakly bound vibrational states are displayed ($v$, $v'$, and $v"$ for the three potentials, as labeled). (b) The Rabi frequency ($\Omega_1$, $\Omega_2$) and detuning ($\delta_1$, $\delta_2$, $\delta$) scheme for photoassociative Autler-Townes spectroscopy.
• Figure 3: Autler-Townes doublet peak positions for the $1_u(-1)$ and $X(-3)$ pair of states. Example scans are shown in insets.
• Figure 4: All Autler-Townes doublet separation parabolas. The minima of the parabolas are proportional to the relative transition strengths. The quantum numbers in parentheses correspond to ($v,J$).
• Figure 5: Spectra of Raman transitions between weakly bound states at operational intensities for (a) $v=-2\rightarrow v=-1$ and (b) $v=-2\rightarrow v=-3$. Black points are (a) natural logarithm of normalized signal and (b) normalized signal versus $\delta$. Fitted curves have (a) Lorentzian and (b) Rabi lineshapes. The error bars display standard error of the mean.