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Acta Physica Sinica

Adiabatic fidelity for atom-dimer conversion system in stimulated Raman adiabatic passage

Shao-Ying Meng, Wu Wei, (1)辽宁大学物理学院,沈阳 110036; (2)中国工程物理研究院北京研究生部,北京 100088;辽宁大学物理学院,沈阳 110036

Published Jan 1, 2009• 11 citations
Publisher

Abstract

From the non-U(1) invariance of the atom-dimer conversion system, we generalized the definition of fidelity to this nonlinear system. By making use of the adiabatic fidelity, we investigated the dynamics and adiabaticity of the atom-dimer conversion system in a stimulated Raman adiabatic passage (STIRAP). We found that the adiabatic fidelity for the coherent population trapping state or dark state, as the function of the adiabatic parameter, approaches to unity following a power law. The power exponent, however, is much smaller than that predicted by the linear adiabatic theorem. We further discuss how to achieve higher adiabatic fidelity for the dark state through optimizing the external parameters of STIRAP and hence to optimize the adiabaticity of the system and obtain high conversion efficiency.

DOI
10.7498/aps.58.5311

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Acta Physica Sinica•Jan 1, 2018•0 citations
From the non-U(1) invariance of the atom-dimer conversion system, we generalized the definition of fidelity to this nonlinear system. By making use of the adiabatic fidelity, we investigated the dynamics and adiabaticity of the atom-dimer conversion system in a stimulated Raman adiabatic passage (STIRAP). We found that the adiabatic fidelity for the coherent population trapping state or dark state, as the function of the adiabatic parameter, approaches to unity following a power law. The power exponent, however, is much smaller than that predicted by the linear adiabatic theorem. We further discuss how to achieve higher adiabatic fidelity for the dark state through optimizing the external parameters of STIRAP and hence to optimize the adiabaticity of the system and obtain high conversion efficiency.
By generalizing the definition of fidelity for the nonlinear system, we investigate the dynamics and adiabaticity of the population transfer for atom-molecule three-level $\ensuremath{\Lambda}$ system on a stimulated Raman adiabatic passage (STIRAP). We find that the adiabatic fidelity for the coherent population trapping state or dark state, as the function of the adiabatic parameter, approaches to unit in a power law. The power exponent, however, is much less than the prediction of the linear adiabatic theorem. We further discuss how to achieve higher adiabatic fidelity for the dark state through optimizing the external parameters of the STIRAP.
We investigate the linear instability and the adiabatic fidelity of a dark state in a nonlinear atom-trimer conversion that is implemented by a stimulated Raman adiabatic passage (STIRAP). We find that the interparticle interactions could induce the instability of the atom-trimer dark state in some parameter regimes. We also discuss the adiabatic evolution of the dark state in terms of a newly defined adiabatic fidelity. Based on our theoretical analysis, we propose a feasible two-photon STIRAP scheme that has high adiabatic fidelity, less instability, and therefore could yield high atom-trimer conversion efficiency.
The adiabaticity of the stimulated Raman adiabatic passage (STIRAP) for the 87Rb atom–molecule conversion in a condensate system is investigated in terms of a newly defined adiabatic fidelity. The evolution of the dark state in the STIRAP is simulated numerically by considering the interparticle interactions and spontaneous emissions of the excited molecular state. We find that these terms will reduce the adiabatic fidelity; however, one can still achieve higher adiabatic fidelity through optimizing the external parameters of the STIRAP. Our discussions are helpful in obtaining higher conversion efficiency from an atomic Bose–Einstein condensate to its molecular counterpart in experiment.
We investigate the adiabaticity of the dark state in a nonlinear atom-trimer conversion system in a stimulated Raman adiabatic passage (STIRAP). We find that, in the absence of the nonlinear collisions, the adiabatic condition for this nonlinear system only depends on the Rabi-frequency of the dimer-trimer coupling optical field, which is different from traditional STIRAP processes. In the presence of the nonlinear collisions, the adiabatic condition also relies on the atom-dimer coupling Rabi frequency. However, its influence is really small. Moreover, we propose a more feasible two-photon STIRAP scheme that has better adiabaticity and hence could yield higher atom-trimer conversion efficiency.
A comprehensive study of two simultaneous three wave mixing processes, a second harmonic generation followed by difference frequency generation, under nonlinear stimulated Raman adiabatic passage (STIRAP) is presented. An input pump is up-converted to its second harmonic, which then gets down-converted to a signal and idler pair with frequencies lying very close to the input pump in such a manner that complete conversion from the pump to the signal and idler takes place without exciting the second harmonic under counterintuitive adiabatic passage. This process involves nonlinear STIRAP with a nonlinear dark state similar to atomic population transfers, and we bring an analogy from atomic systems to our nonlinear dynamics to linearize the problem and analytically obtain the adiabaticity condition required for complete conversion. We also show that the nonlinear STIRAP mechanism results in a large bandwidth of about 380 nm with almost complete conversion of the pump to the signal and idler.
On the basis of the stimulated Raman adiabatic passage technology, we study the conversion of ultracold atoms into diatomic molecules by using a square-shaped pulse field. By the method of adiabatic fidelity, we analyze the dynamical evolution process of the coherent population trapping state for the atom-molecule conversion system. We introduce two adiabatic fidelities to describe the efficiency of ultracold atom-molecule conversion, i.e.:1) the final adiabatic fidelity, which gives the value of the adiabatic fidelity at the end of the evolution:the closer to 1 it is, the higher the conversion efficiency is; 2) the final maximum adiabatic fidelity, which denotes the maximum value that can be achieved at the end of evolution, indicating the highest conversion efficiency. With these two quantities, we discuss how to achieve higher adiabatic fidelity for the coherent population trapping state through optimizing the pulse-delay time and the pulse-laser intensity of the stimulated Raman adiabatic passage. In addition, we also discuss the effects of the width of pulses on the ultracold atom-molecule conversion efficiency and the feasibility of continuous light. It is shown that the final adiabatic fidelity of the coherent population trapping state demonstrates a large periodic oscillation with the pulse-laser intensity. By calculating and analyzing the final adiabatic fidelity and the final maximum adiabatic fidelity, we obtain the conditions for higher efficiency conversion, which gives the best choice of the pulse-laser intensity, the pulse-delay time, and the width of pulses. The results show that the scheme of square-shaped pulses we discussed has obvious advantages compared with that of Gaussian-shaped pulses, which can achieve high adiabatic fidelity and realize higher ultracold atom-molecule conversion efficiency via employing the pulse-laser field with low intensity. Further detailed comparison between the square-shaped pulses and the Gaussian-shaped pulses is also given. Particularly, we find that the final adiabatic fidelity shows a periodic oscillation with the pulse width, which means that the high efficiency atom-molecule conversion can be achieved by using a pulse field with small width. Moreover, we find that the high efficiency conversion can also be achieved by using special continuous light under certain conditions.