  We observe and control a molecular vibrational wave packet in an
electronically excited state of the neutral hydrogen molecule. In an
extreme-ultraviolet (XUV) transient-absorption experiment we launch a
vibrational wave packet in the $D ^1\Pi_u 3p\pi$ state of H$_2$ and observe its
time evolution via the coherent dipole response. The reconstructed
time-dependent dipole from experimentally measured XUV absorption spectra
provides access to the revival of the vibrational wave packet, which we control
via an intense near-infrared (NIR) pulse. Tuning the intensity of the NIR pulse
we observe the revival of the wave packet to be significantly modified, which
is supported by the results of a multi-level simulation. The NIR field is
applied only 7 fs after the creation of the wave packet but influences its
evolution up to at least its first revival at 270 fs. This experimental
approach for nonlocal-in-time laser control of quantum dynamics is generally
applicable to a large range of molecules and materials as it only requires the
observation of absorption spectra.
