  Polar molecules are a quantum resource with rich internal structure that can
be coherently controlled. The structure, however, also makes the state
preparation and measurement (SPAM) of molecules challenging. We advance the
SPAM of individual molecules assembled from constituent atoms trapped in
optical tweezer arrays. Sites without NaCs molecules are eliminated using
high-fidelity Cs atom detection, increasing the peak molecule filling fraction
of the array threefold. We site-selectively initialize the array in a
rotational qubit subspace that is insensitive to differential AC Stark shifts
from the optical tweezer. Lastly, we detect multiple rotational states per
experimental cycle by imaging atoms after sequential state-selective
dissociations. These demonstrations extend the SPAM capabilities of molecules
for quantum information, simulation, and metrology.
