Assembly of a Rovibrational Ground State Molecule in an Optical Tweezer

We demonstrate the coherent creation of a single NaCs molecule in its rotational, vibrational, and electronic (rovibronic) ground state in an optical tweezer. Starting with a weakly bound Feshbach molecule, we locate a two-photon transition via the $|c^3{\mathrm{\Sigma }}_1,v^{\prime }=26⟩$ excited state and drive coherent Rabi oscillations between the Feshbach state and a single hyperfine level of the NaCs rovibronic ground state $|X^1\mathrm{\Sigma },v^{\prime \prime }=0,N^{\prime \prime }=0⟩$ with a binding energy of $D_0=h\times 147044.63(11)\mathrm{GHz}$. We measure a lifetime of $3.4\pm 1.6\mathrm{s}$ for the rovibronic ground state molecule, which possesses a large molecule-frame dipole moment of 4.6D and occupies predominantly the motional ground state. These long-lived, fully quantum-state-controlled individual dipolar molecules provide a key resource for molecule-based quantum simulation and information processing.

Figure 1

Schematic overview of assembling rovibronic ground state molecules in optical tweezers. (a) Sequence of molecular assembly from individually trapped atoms to ground state molecule. This work focuses on the outlined final step of internal state transfer. (b) Selected potential curves of the NaCs molecule, showing the Raman transfer scheme from the Feshbach state to the rovibronic ground state via $|c^3{\mathrm{\Sigma }}_1,v^{\prime }=26⟩$. Pump and Stokes laser Rabi frequencies are labeled ${\mathrm{\Omega }}_P$ and ${\mathrm{\Omega }}_S$, respectively. Inset: Geometry of the optical tweezer, magnetic bias field, and Raman transfer lasers.

Figure 2

Characterization of the $|c^3{\mathrm{\Sigma }}_1,v^{\prime }=26⟩$ state of NaCs by depletion of Feshbach molecules. (a) Depletion spectrum near 325 130 GHz using ${\sigma }^{+}+{\sigma }^{-}$ polarization, showing $J^{\prime }=1$, 2 rotational levels and Zeeman structure with approximate quantum number assignments. The curve is a theory prediction based on a model of the Feshbach and $c^3{\mathrm{\Sigma }}_1$ states [48]. (b) Linewidth characterization of the $J^{\prime }=1,M_J^{\prime }=1$ level of $|c^3{\mathrm{\Sigma }}_1,v^{\prime }=26⟩$ used for Raman transfer when probed with ${\sigma }^{+}$ polarization. The curve is a fit to a Lorentzian line shape, with fit linewidth $\mathrm{\Gamma }=2\pi \times 120(30)\mathrm{MHz}$. (c) Characterization of the single-photon scattering rate $R_{\mathrm{sc}}$ due to the pump laser when red-detuned from $|c^3{\mathrm{\Sigma }}_1,v^{\prime }=26⟩$. The curve is a fit to the scattering rate derived from the same model as in part (a). Inset: the linear dependence of the scattering rate on the pump laser power at the $-21\mathrm{GHz}$ detuning is consistent with single-photon scattering. Error bars on all data are Wilson score intervals for the binomially distributed $\mathrm{Na}+\mathrm{Cs}$ survival probability.

Figure 3

(a) Raman resonance and (b) Raman Rabi oscillation between the Feshbach state and the rovibronic ground state of NaCs via $|c^3{\mathrm{\Sigma }}_1,v^{\prime }=26⟩$. Dashed lines and gray bars show the Feshbach molecule contrast, which was collected simultaneously with the data in (b) and is shown there by the first blue circle and orange triangle. The data are simultaneously fit to a Rabi line shape including loss and decoherence.

Figure 4

Characterization of the lifetime of a rovibronic ground state NaCs molecule in an optical tweezer at different values of the trap intensity. Atomic background has been subtracted. Inset: the increase in molecule loss rate with laser intensity is consistent with a linear trend corresponding to one-photon scattering.