Coherent control with shaped femtosecond laser pulses applied to ultracold molecules

Abstract

We report on coherent control of excitation processes of translationally ultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond laser pulses. Evolution strategies are applied in a feedback loop in order to optimize the photoexcitation of the Rb2 molecules, which subsequently undergo ionization or fragmentation. A superior performance of the resulting pulses compared to unshaped pulses of the same pulse energy is obtained by distributing the energy among specific spectral components. The demonstration of coherent control to ultracold ensembles opens a path to actively influence fundamental photo-induced processes in molecular quantum gases.

Short-pulse photoassociation in rubidium below theD1line

“…In particular, a setup such as in Refs. [19,20] was considered. All potentials into which population can be excited by a laser field were included in the model.…”

“…It is noteworthy that this region of small detunings where PA is most efficient is unlikely to be accessible in an experiment with short pulses due to the bandwidth of the pulse. Such pulses contain spectral components corresponding to the atomic resonance, which can destroy the MOT [19,20]. The pulse therefore has to be either fardetuned from the atomic line or the resonant spectral components have to be filtered out.…”

“…In a subsequent stabilization step, molecules in the singlet ground state or in the lowest triplet state are created by spontaneous or stimulated emission. Photoassociation with short laser pulses on cold systems has sparked interest from both experiment [8,16,19,20] and theory [13,14,15,25,26,27]. Specifically, a pump-dump scheme has been suggested with the idea to create a wavepacket on the excited state and make use of its timedependence for efficient stabilization [14,15,27].…”

“…This is because the dynamical timescales of cold systems are simply much larger than the ultrashort timescale of femtoseconds. The adaptation of pulse shaping techniques known from coherent control to ultracold systems is a subject of current investigation [19,20]. In addition to controlling nuclear dynamics, a femtosecond laser can be employed for high-resolution spectroscopy in ultracold systems by utilizing it as a frequency comb [21].…”

“…Formation of molecules in both the singlet ground state X 1 Σ + g and the lowest triplet state a 3 Σ + u can then be tested. Rubidium has been chosen since experimental effort is under way for this species [19,20]. A comprehensive model of the interaction of two atoms with a laser field is developed and the role of all laser parameters is analyzed.…”