Narrow Results

We present an approach for effectively converting atomic Bose–Einstein condensate (BEC) into molecular one. Atoms are converted into molecules through a series of intermediate vibrational states by using chainwise stimulated Raman adiabatic passage technique. We utilize a feasible pulse sequence to achieve higher conversion efficiency by solving the coupled mean-field equations. As an example, we investigate the formation of Rb₂ and calculate conversion efficiency to be 92.3%.

We investigate theoretically the preparation of ultracold photoassociated Cs₂ molecules in the lowest vibrational level of the ground electronic state via the stimulated Raman adiabatic passage (STIRAP) by solving the time-dependent Schrödinger equation using the mapped Fourier grid method. A negative chirped laser pulse is used to produce the unstable photoassociated molecules in the excited electronic state. A dump pulse is utilized to transfer a partial population of the unstable photoassociated molecules to the vibrational v″ = 18 level of the ground electronic state. This part of population is then transferred to the v″ = 0 level of the ground electronic state by the pump and Stokes laser pulses via an intermediate state which is taken to be the v′ = 7 level of the excited electronic state, forming the stable photoassociated molecules. The population transfer efficiency from v″ = 18 to v″ = 0 in the ground electronic state reaches 96.2% via the STIRAP.

This work explores the vibrational state-selective photoassociation (PA) in the ground state of the HX (X = F, Cl, I) molecule by solving the time-dependent Schrödinger equation. For the three systems, the vibrational level of $v=17$ is set to be the target state and the PA probability of the target state is calculated and compared by considering different initial collision momentums. It is found that the PA probabilities are in accordance with Franck–Condon overlap integral for the HI and HCl systems, but it is not the case for the HF system. Moreover, for the HF system, it is shown that the PA probability of the target state is largest and the multiphoton transition is more likely to occur.

Photoassociation of ultracold atoms has been used to determine interaction potentials and to extract scattering lengths with great precision, which we discuss here in the context of lithium. We also describe a recent experiment where saturation in the rate of photoassociation of an atomic BEC was observed.

One of the many important contributions of Alex Dalgarno to Atomic, Molecular, and Optical (AMO) Physics relates to his work on ultracold physics. After a brief review of his early work on photoassociation (PA) of ultracold atoms and the formation of ultracold molecules, a short description of new results using Feshbach Optimized Photoassociation (FOPA) will be given. This research points to Alex's influence on the work now performed in my group at UConn.

Lithium-7 exhibits a broad Feshbach resonance that we exploit to tune the interactions in a Bose-Einstein condensate (BEC). We find that the rate of photoassociation can be enhanced by several orders of magnitude by tuning close to the resonance, and use this effect to observe saturation in the rate of association of a BEC for the first time. We have also used a lithium BEC to explore the effects of disorder on the transport and coherence properties of the condensate. We also show that the scattering length goes through a shallow zero-crossing far from the resonance, where it may be made positive or negative with a magnitude of less than 0.1 a_o, and have made preliminary transport measurements in the regime of weak repulsive and attractive interactions.

When ultracold (T < 1 mK) molecules are formed by photoassociation (PA) followed by spontaneous emission, they commonly are formed in high vibrational levels, typically within 30 cm^-1 of the dissociation limit.^1,2 Such levels are difficult to produce in other ways, and, because their bands include only a few rotational quantum numbers (typically < 5 for KRb at 0.2 mK), their electronic spectra are readily assignable, especially when accurate ab initio calculations are also available. Research at the University of Connecticut has demonstrated how the spectroscopy of KRb ultracold molecules formed by PA^3,4 can be studied using multiple resonance spectroscopy.^1,5–7

Recently, there has been important progress in the formation of ultracold polar molecules in the rovibrational ground state, thus opening intriguing perspectives for the investigation of strongly correlated quantum systems under the influence of long-range dipolar forces. After an brief introduction into the field of ultracold molecules, we will review our recent experiments on the formation of ultracold LiCs molecules in the absolute ground state X¹Σ⁺, v = 0, J = 0 via a single photo-association step starting from laser-cooled atoms.