  Tunnel ionization of room-temperature D$_2$ in an ultrashort (12 femtosecond)
near infra-red (800 nm) pump laser pulse excites a vibrational wavepacket in
the D2+ ions; a rotational wavepacket is also excited in residual D2 molecules.
Both wavepacket types are collapsed a variable time later by an ultrashort
probe pulse. We isolate the vibrational wavepacket and quantify its evolution
dynamics through theoretical comparison. Requirements for quantum computation
(initial coherence and quantum state retrieval) are studied using this
well-defined (small number of initial states at room temperature, initial
wavepacket spatially localized) single-electron molecular prototype by
temporally stretching the pump and probe pulses.
