  Qubit coherence times are critical to the performance of any robust quantum
computing platform. For quantum information processing using arrays of polar
molecules, a key performance parameter is the molecular rotational coherence
time. We report a 93(7) ms coherence time for rotational state qubits of laser
cooled CaF molecules in optical tweezer traps, over an order of magnitude
longer than previous systems. Inhomogeneous broadening due to the differential
polarizability between the qubit states is suppressed by tuning the tweezer
polarization and applied magnetic field to a "magic" angle. The coherence time
is limited by the residual differential polarizability, implying improvement
with further cooling. A single spin-echo pulse is able to extend the coherence
time to nearly half a second. The measured coherence times demonstrate the
potential of polar molecules as high fidelity qubits.
