Suppression of ultracold ground-state hyperfine-changing collisions with laser light

Complete Quantum Coherent Control of Ultracold Molecular Collisions

We show that quantum interference-based coherent control is a highly efficient tool for tuning ultracold molecular collision dynamics that is free from the limitations of commonly used methods that rely on external electromagnetic fields. By varying the relative populations and phases of initial coherent superpositions of degenerate molecular states, we demonstrate complete coherent control over integral scattering cross sections in the ultracold s-wave regime of both the initial and final collision channels. The proposed control methodology is applied to ultracold O_{2}+O_{2} collisions, showing extensive control over s-wave spin-exchange cross sections and product branching ratios over many orders of magnitude.

Engineering Excited-State Interactions at Ultracold Temperatures

Using a recently developed method for precisely controlling collision energy, we observe a dramatic suppression of inelastic collisions between an atom and ion (Ca+Yb^{+}) at low collision energy. This suppression, which is expected to be a universal phenomenon, arises when the spontaneous emission lifetime of the excited state is comparable to or shorter than the collision complex lifetime. We develop a technique to remove this suppression and engineer excited-state interactions. By dressing the system with a strong catalyst laser, a significant fraction of the collision complexes can be excited at a specified atom-ion separation. This technique allows excited-state collisions to be studied, even at ultracold temperature, and provides a general method for engineering ultracold excited-state interactions.

Formation of ultracold Rb2 molecules in the v'' = 0 level of the a(3)Σ+(u) state via blue-detuned photoassociation to the 1(3)Π(g) state

We report on the observation of blue-detuned photoassociation in Rb(2), in which vibrational levels are energetically above the corresponding excited atomic asymptote. (85)Rb atoms in a MOT were photoassociated at short internuclear distance to levels of the 1(3)Π(g) state at a rate of approximately 5 × 10(4) molecules s(-1). We have observed most of the predicted vibrational levels for all four spin-orbit components; 0(+)(g), 0(-)(g), 1(g), and 2(g), including levels of the 0(+)(g) outer well. These molecules decay to the metastable a(3)Σ(+)(u) state, some preferentially to the v'' = 0 level, as we have observed for photoassociation to the v' = 8 level of the 1(g) component.

Manipulation of cold atomic collisions by cavity QED effects

We show how the dynamics of collisions between cold atoms can be manipulated by a modification of spontaneous emission times. This is achieved by placing the atomic sample in a resonant optical cavity. Spontaneous emission is enhanced by a combination of multiparticle entanglement together with a higher density of modes of the modified vacuum field, in a situation akin to superradiance. A specific situation is considered and we show that this effect can be experimentally observed as a large suppression in trap-loss rates.

Photoassociation of Ultracold Atoms: A New Spectroscopic Technique

The new spectroscopic technique of photoassociation of ultracold atoms is reviewed, with an emphasis on connecting this area to traditional bound-state molecular spectroscopy. In particular, in contrast to photoassociative spectra at thermal energies, which are broad and of low information content, photoassociative spectra of ultracold atoms are high resolution, permitting observation of small vibrational and rotational spacings of long-range molecular levels near dissociation (typically with outer classical turning points >20 Å). The types of detection and theoretical analysis employed are illustrated, primarily using the example of 39K2. Future directions and applications of this field (e.g., to ultracold molecular formation) are also discussed. Copyright 1999 Academic Press.