  In a recent paper, Wicht, L\"ammerzahl, Lorek, and Dittus [Phys. Rev. {\bf A
78}, 013610 (2008)] come to the conclusion that a molecular
rotational-vibrational quantum interferometer may possess the sensitivity
necessary to detect gravitational waves. We do not agree with their results and
demonstrate here that the true sensitivity of such interferometer is many
orders of magnitude worse than that claimed in the mentioned paper. In the
present comment we estimate the expected energy shifts and derive equations of
motion for a quantum symmetric top (diatomic molecule or deformed nucleus) in
the field of gravitational wave, and then estimate the sensitivity of possible
experiments.
