Laser cooling with adiabatic passage for type-II transitions
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Front. Phys. 16(3), 32501 (2021)
Research article Laser cooling with adiabatic passage for type-II transitions Qian Liang1 , Tao Chen1,† , Wen-Hao Bu1 , Yu-He Zhang1 , Bo Yan1,2,3,‡ 1
Interdisciplinary Center of Quantum Information, State Key Laboratory of Modern Optical Instrumentation, Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China 2 Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing 210093, China 3 Key Laboratory of Quantum Optics, Chinese Academy of Sciences, Shanghai 200800, China Corresponding authors. E-mail: † [email protected], ‡ [email protected] Received August 3, 2020; accepted October 15, 2020
We extend the idea of laser cooling with adiabatic passage to multi-level type-II transitions. We find the cooling force can be significantly enhanced when a proper magnetic field is applied. That is because the magnetic field decomposes the multi-level system into several two-level sub-systems, hence the stimulated absorption and stimulated emission can occur in order, allowing for the multiple photon momentum transfer. We show that this scheme also works on the laser-coolable molecules with a better cooling effect compared to the conventional Doppler cooling. A reduced dependence on spontaneous emission based on our scheme is observed as well. Our results suggest this scheme is very feasible for laser cooling of polar molecules. Keywords laser cooling of polar molecule, adiabatic passage, type-II transition, cold molecule, cold atom
1 Introduction Allowing fast producing and precise manipulation of cold atomic samples [1–3], laser cooling technique has revolutionized the field of atomic, molecular, optical and quantum physics during last several decades [4–8]. For conventional Doppler cooling on atoms such as alkali atoms, the main cooling laser is typically red-detuned with only single frequency (without consideration on the repump laser). It is good enough for most laser-coolable atomic species. But for some special cases, multi-frequency cooling schemes [9], including adiabatic rapid passage [10–12] and bichromatic force [13–16], have been proposed and predicted to have a better performance, but with the price of increasing the complexity of the system. However, some features, for example, stronger cooling forces and a weak dependence on spontaneous emission [9], make them potentially be applied to direct laser cooling of molecules where the cooling transition is quasi-closed [17–20]. Besides the leakage channels, the energy levels for molecules are complicated and the type-II transitions (in which the total angular momentum quantum number in the ground state J is no less than that in the excited state J ′ ) are dominant [21, 22], making the cooling process much more ∗ arXiv:
1902.05212. This article can also be found at http:// journal.hep.com.cn/fop/EN/10.1007/s11467-020-1019-8.
complex and the Doppler cooling force much weaker than those in atoms. To achieve a better coolin
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