Rosen-Zener model in cold molecule formation

TL;DR

This paper analyzes the Rosen-Zener model for atom-to-molecule conversion in Bose-Einstein condensates, deriving formulas for transition probabilities and revealing different dynamical regimes depending on detuning and field strength.

Contribution

It provides new analytic formulas for molecular state probability in both weak and strong coupling limits, and uncovers a hidden singularity affecting the system's dynamics.

Findings

At large detuning, molecule formation is nearly non-oscillatory and limited to one-third of atoms.

At small detuning, the system exhibits large-amplitude oscillations between atomic and molecular states.

A hidden singularity influences the qualitative behavior of the model.

Abstract

The Rosen-Zener model for association of atoms in a Bose-Einstein condensate is studied. Using a nonlinear Volterra integral equation, we obtain an analytic formula for final probability of the transition to the molecular state for weak interaction limit. Considering the strong coupling limit of high field intensities, we show that the system reveals two different time-evolution pictures depending on the detuning of the frequency of the associating field. For both limit cases we derive highly accurate formulas for the molecular state probability valid for the whole range of variation of time. Using these formulas, we show that at large detuning regime the molecule formation process occurs almost non-oscillatory in time and a Rosen-Zener pulse is not able to associate more than one third of atoms at any time point. The system returns to its initial all-atomic state at the end of the process and the maximal transition probability is achieved when the field intensity reaches its peak. In contrast, at small detuning the evolution of the system displays large-amplitude oscillations between atomic and molecular populations. We find that the shape of the oscillations in the first approximation is defined by the field detuning only. Finally, a hidden singularity of the Rosen-Zener model due to the specific time-variation of the field amplitude at the beginning of the interaction is indicated. It is this singularity that stands for many of the qualitative and quantitative properties of the model. The singularity may be viewed as an effective resonance-touching.