Breathing mode excitation in near-harmonic systems: resonant mass capture, desorption and atoms in optical lattices

Abstract

The phenomenon of breathing mode excitation or bound-state wavepacket squeezing and spreading driven by a time-dependent oscillator frequency (due to either a transient force constant or mass) is considered here. An easily implemented theory of stimulated wavepacket dynamics for near-harmonic systems is presented which describes a variety of generic time dependences such as single sudden excitation, double switching (excitation/time delay/de-excitation) and decaying initially excited states which characterize many processes in spectroscopy, pump-probe control in intramolecular dynamics, and femtochemistry. The model is used as the theoretical basis for understanding such diverse phenomena as quantum excitation due to temporary neutron capture, stimulated bond-breaking resulting in delocalization, desorption, or dissociation, and breathing mode excitation of ultracold atoms trapped in optical lattices. Whilst the first two examples are speculative, results for transient wavepacket dynamics of the occupied excited optical lattice are in accord with recent experimental observations reported by the NIST Laser Cooling Group. Emphasis on the inherent theoretical simplicity and the multidisciplinary aspects of near-harmonic breathing mode excitation, as exemplified by the specific realizations considered here, has been a major intent of this topical review.

Ultrafast X-Ray Scattering in Solids

“…For the case in which the frequency does not go all the way to zero, one would expect impulsive softening to induce oscillations in the rms displacement about the new equilibrium value. Such oscillations have been observed for atoms trapped in optical lattices [167,169,170]. The oscillations probed in the Bragg-scattered light correspond to breathing-mode excitations in atomic wavepackets.…”

“…We note that a similar time-dependent DW model has been applied to describe visible-light Bragg scattering off atoms trapped in optical lattices [166,167]. On turning off the light-induced potential, the rms displacement of the atoms again increases inertially, with the velocity set by the initial temperature of the lattice.…”