  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 $|{c^3\Sigma,v'=26}\rangle$ excited state and drive coherent
Rabi oscillations between the Feshbach state and a single hyperfine level of
the NaCs rovibronic ground state $|{X^1\Sigma,v''=0,N''=0}\rangle$ with a
binding energy of $D_0 = h \times 147038.30(2)$ GHz. We measure a lifetime of
$3.4\pm1.6$ s for the rovibronic ground-state molecule, which possesses a large
molecule-frame dipole moment of 4.6 Debye 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.
