Photodissociation of ultracold diatomic strontium molecules with quantum state control

Abstract

Chemical reactions at ultracold temperatures are expected to be dominated by quantum mechanical effects. Although progress towards ultracold chemistry has been made through atomic photoassociation, Feshbach resonances and bimolecular collisions, these approaches have been limited by imperfect quantum state selectivity. In particular, attaining complete control of the ground or excited continuum quantum states has remained a challenge. Here we achieve this control using photodissociation, an approach that encodes a wealth of information in the angular distribution of outgoing fragments. By photodissociating ultracold (88)Sr2 molecules with full control of the low-energy continuum, we access the quantum regime of ultracold chemistry, observing resonant and nonresonant barrier tunnelling, matter-wave interference of reaction products and forbidden reaction pathways. Our results illustrate the failure of the traditional quasiclassical model of photodissociation and instead are accurately described by a quantum mechanical model. The experimental ability to produce well-defined quantum continuum states at low energies will enable high-precision studies of long-range molecular potentials for which accurate quantum chemistry models are unavailable, and may serve as a source of entangled states and coherent matter waves for a wide range of experiments in quantum optics.

Perspective: Ultracold molecules and the dawn of cold controlled chemistry

“…The translationally cold photofragments emerge as a coherent superposition of matter waves and their angular distribution is accurately reproduced by quantum calculations. 125 However, as expected, quasiclassical descriptions were not successful in describing the observed angular distribution. With improved imaging techniques and trapping methods, it might be possible to create photofragments in an optical lattice in well-defined quantum states with nanokelvin kinetic energies.…”

“…Such an experiment was recently reported by McDonald et al 125 in which ultracold Sr 2 dimers were created by photoassociation of laser cooled Sr atoms in a far-off resonant optical lattice. The strontium dimers are not covalently bound but have dissociation energies similar to hydrogen bonded water dimers.…”

Optical Feshbach resonances and ground-state-molecule production in the RbHg system

“…Ultracold molecules offer the possibility to the study of chemistry under yet unexplored conditions: at extremely low energies and in controllable quantum states, and where the chemical reaction could be manipulated with external magnetic, or electric fields. Recent experimental realizations include reactive collisions of KRb molecules [5], or the photodissociation of Sr 2 molecule [6]. Finally, ultracold molecules offer new avenues and improved precision in experimental searches of "new physics".…”

“…Our work is motivated by the experimental progress in the trapping of Rb and Hg atoms in a dual magneto-optical trap (MOT) which was made recently in our group [33]: approximately 10 6 Rb atoms were trapped simultaneously with about 10 5 Hg atoms. Among atoms that can be laser cooled, Hg has particularly interesting properties.…”

Transition moments between excited electronic states from the Hermitian formulation of the coupled cluster quadratic response function

“…Until recently, properties of the excited electronic states were not easily available in high-resolution experiments, but with the advances of new spectroscopic techniques in the hot pipe 4? -7 and ultracold experiments, [8][9][10][11][12] more and more accurate experimental data become available and possibly need theoretical interpretation. Theoretical information about the transition moments between the excited states is also necessary to propose new routes to obtain molecules in the ground rovibrational state (see, e.g., Ref.…”