Liu Lan, Zhang De-Chao, Yang Huan, Liu Ya-Xiong, Nan Jue, Rui Jun, Zhao Bo, Pan Jian-Wei
Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Shanghai Branch, CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.
Phys Rev Lett. 2019 Jun 28;122(25):253201. doi: 10.1103/PhysRevLett.122.253201.
Stimulated Raman adiabatic passage (stirap) allows efficiently transferring the populations between two discrete quantum states and has been used to prepare molecules in their rovibrational ground state. In realistic molecules, a well-resolved intermediate state is usually selected to implement the resonant stirap. Because of the complex molecular level structures, the detuned stirap always coexists with the resonant stirap and may cause unexpected interference phenomenon. However, it is generally accepted that the detuned stirap can be neglected if compared with the resonant stirap. Here we report on the first observation of interference between the resonant and detuned stirap in the adiabatic creation of ^{23}Na^{40}K ground-state molecules. The interference is identified by observing that the number of Feshbach molecules after a round-trip stirap oscillates as a function of the hold time, with a visibility of about 90%. This occurs even if the intermediate excited states are well resolved, and the single-photon detuning of the detuned stirap is about 1 order of magnitude larger than the linewidth of the excited state and the Rabi frequencies of the stirap lasers. Moreover, the observed interference indicates that if more than one hyperfine level of the ground state is populated, the stirap prepares a coherent superposition state among them, but not an incoherent mixed state. Further, the purity of the hyperfine levels of the created ground state can be quantitatively determined by the visibility of the oscillation.
受激拉曼绝热通道（STIRAP）能够有效地在两个分立量子态之间转移粒子数，并且已被用于制备处于振转基态的分子。在实际分子中，通常会选择一个分辨率良好的中间态来实现共振STIRAP。由于分子能级结构复杂，失谐STIRAP总是与共振STIRAP共存，并且可能会导致意想不到的干涉现象。然而，一般认为与共振STIRAP相比，失谐STIRAP可以忽略不计。在此，我们报告了在绝热制备(^{23}Na^{40}K)基态分子过程中首次观察到共振STIRAP与失谐STIRAP之间的干涉。通过观察往返STIRAP后费什巴赫分子的数量随保持时间振荡，且可见度约为90%，从而识别出这种干涉。即使中间激发态分辨率良好，且失谐STIRAP的单光子失谐比激发态的线宽以及STIRAP激光的拉比频率大约一个数量级，这种干涉仍然会出现。此外，观察到的干涉表明，如果基态的多个超精细能级被占据，STIRAP会在它们之间制备一个相干叠加态，而不是一个非相干混合态。此外，通过振荡的可见度可以定量确定所制备基态超精细能级的纯度。
