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Acta Physica Sinica

Effect of external field shape on the ultracold atom-polymer molecule conversion efficiency

Zhao Xiu-Niao, Sun Jian-An, Dou Fu-Quan

Published Jan 1, 2014• 0 citations
Publisher

Abstract

By changing the Rabi frequency of the photoassociation laser and the atom-polymer coupling strength, we investigate the effect of external field shape on atom-polymer conversion efficiency. First, by defining time-index, the external filed shape given in literature is improved. We discuss the influence of time-index on conversion efficiency, and then choose a more optimized external filed shape, it has good parameter robustness. Under the action of the external field, the adiabatic process has almost no oscillation, the adiabatic fidelity is close to 1, and the error of the system is less. The ultracold atom-polymer molecules conversion can be realized stably and efficiently.

DOI
10.7498/aps.63.220302

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By changing the Rabi frequency of the photoassociation laser and the atom-polymer coupling strength, we investigate the effect of external field shape on atom-polymer conversion efficiency. First, by defining time-index, the external filed shape given in literature is improved. We discuss the influence of time-index on conversion efficiency, and then choose a more optimized external filed shape, it has good parameter robustness. Under the action of the external field, the adiabatic process has almost no oscillation, the adiabatic fidelity is close to 1, and the error of the system is less. The ultracold atom-polymer molecules conversion can be realized stably and efficiently.
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We investigate the effects of external field parameters, including the strength of Rabi pulse, its width, and single-photon detuning, on conversion from ultracold atoms to heteronuclear triatomic molecules by two-photon stimulated Raman adiabatic passage. It is found that the conversion efficiency of the system decreases first with the strength of the Stokes pulse increasing, then oscillates, and finally approaches a stable value, which is less than 1. But for the pump pulse, the efficiency first increases with the increase of the pulse intensity, and then approaches 1 quickly. The results show that the two pulses play different roles in the conversion. The pulse width can not only determine the final conversion efficiency, but also be used to reflect the time needed for stable conversion. The system has a higher efficiency of conversion for red detuning pump laser, but the blue detuning is not conducive to the formation of the molecules. In addition, the differences of the adiabaticity and conversion efficiency among different reaction pathways are discussed.
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Due to the inevitability of nonlinear collisions between particles in ultracold atomic condensate experiments, it is of great significance to study the nonlinear effect for producing ultracold molecules from atomic condensates. In this work, we investigate theoretically the nonlinear effect induced by the two-body collision for producing ultracold Cs2 molecules from ultracold atoms by the stimulated Raman adiabatic passage in a tunneling four-level structure. Under the two-photon resonance condition and the coherent population trapping state, the conversion efficiency is influenced significantly by the nonlinear parameter. Meanwhile, the optimized parameter ranges of the resonance tunneling strength at the unstable excited molecular states, the effective Rabi frequencies of the two-laser fields, and the detuning of the pump field for different nonlinear parameters are suggested to obtain the high conversion efficiency of Cs2 molecules at the ground state. Finally, a maximum conversion efficiency of up to 88.56% can be realized in the optimized parameter ranges.
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