-
在如图1所示的原子系统中,同时引入一束饱和光和一束探测光,频率分别表示为
${\omega _s}$ 和${\omega _p}$ ,其中饱和光用来激发原子,探测光较弱,用来观察原子系统与光场作用后的吸收情况;在模型中,还引用两束耦合光,分别为${\omega _c}$ 和${\omega _d}$ ,其作用是使得不同能级之间发生耦合现象。以上四束光所加的位置如图中所示,失谐关系如下:两束耦合光失谐分别为${\Delta _c} = {\omega _c} - \left( {{\omega _3} - {\omega _2}} \right)$ 和${\Delta _d} = {\omega _d} - \left( {{\omega _4} - {\omega _2}} \right)$ ;探测光和饱和光失谐为${\Delta _p} = {\omega _p} - {\omega _4}$ 和${\Delta _s} = {\omega _s} - {\omega _4}$ ;饱和光、两束耦合光拉比频率分别为${\varOmega_s} = {E_s}{\mu _{14}}/2\hbar$ 、${\varOmega _c} = {E_c}{\mu _{23}}/2\hbar$ 、${\varOmega _d} = {E_d}{\mu _{24}}/2\hbar $ 。根据模型设计的已知条件,且由于探测光较弱,笔者此时忽略它对于整个原子系统产生的影响,可以获得在薛定谔图像下的哈密顿量,进而推出相互作用图像下的表达式,再由密度算符运动方程得出密度矩阵。最后通过拉氏变换法和量子回归理论,同时考虑多普勒效应,得出探测光的吸收谱表达式[10]:$$A = \displaystyle\int\limits_{ - \infty }^{ + \infty } A \left( {{\Delta _p},\upsilon } \right)N(\upsilon ){\rm d}\upsilon = \displaystyle\int\limits_{ - \infty }^{ + \infty } A \left( {{\Delta _p},\upsilon } \right)\dfrac{{{N_0}}}{{u\sqrt {\text{π}} }}{{\rm e}^{ - {\upsilon ^2}/u}}{\rm d}\upsilon $$ (1) ${N_0}$ 为单位体积内原子数;$u$ 为最可几速率。
Tunable light absorption in Ru atomic vapor driven by three coherent fields
-
摘要: 在铷原子蒸汽中,同时引入一束强相干光和两束耦合光共同作用在一个多普勒加宽的四能级N模型原子系统中。在原子系统中通过耦合场的引入以及耦合场强度的调节,观察量子光学现象。首先,由原子模型出发,由哈密顿量方程求得密度矩阵,再经由拉氏变换法求解,得出弱探测光的吸收光谱表达式。在光路设计中,采用耦合光与探测光同向,与饱和光反向传播,通过光场参数的调节,可以观察到六个相干光学烧孔和一个电磁感应光透明窗口。同时,采用了两束耦合光分别和探测光反向、同向传播,饱和光与探测光反向传播。此时在吸收光谱中,将同时出现电磁感应光透明和电磁诱导吸收两种现象。进而,在原子系统中,采用光路的不同搭配,在吸收光谱中可以观测到吸收增强或减弱情况的出现,包括形成烧孔的位置和个数的变化;通过驱动场激发原子的相干跃迁,使得在吸收谱线中同时出现电磁诱导透明和电磁诱导吸收两种吸收特性,并通过光场的调节,数据模拟的比较,分析两种量子相干效应的产生和转换,进行深入研究,并得出结论,这些结果对于现在热门的光学量子存储将有较好的理论指导。Abstract: In recent years, based on the intense interaction between coherent light and matter, the controllable quantum interference phenomena, such as coherent population trapping, electromagnetically induced transparency and electromagnetically induced absorption, optical hole-burning, have attracted a comprehensive concern. For exploring the controllable characteristics of light absorption involving the coherent hole-burning, a four-level N-type atomic system was proposed, which was driven by a strong coherent light field and two coupling fields with the Doppler broadening thermal rubidium vapor. Via introducing the coupling fields and then adjusting the intensity of the coupling field in such an atomic system, some interesting quantum optical phenomena can be observed. Based on the design of this atomic model, the expression of absorption spectrum of the weak probe light fields was derived via the Laplace transform with the system Hamiltonian equation and density matrices. In the design of optical scheme, the saturated light field was inputted with the same or opposite propagating direction as that of the two coupling light fields, which was opposite the weak probe light field. In such a scheme, six coherent optical hole-burnings and one window based on electromagnetically induced transparency may be realized. With the adjustment of the relevant parameters in terms of the intensities and frequencies of the light fields, the enhancement or weakening of the light absorption can be realized in the absorption spectrum, including the change of the position and number of the optical hole-burning. By the transition of atoms excited by the fields, both electromagnetic induced transparency and electromagnetic induced absorption appeared at the same time. Through the adjustment of light field and the comparison of simulation results, the generation and conversion of the two quantum coherence effects were deeply studied. It is concluded that these results may have a good theoretical guidance for the popular optical quantum storage.
-
[1] Putz S, Angerer A,Krimer D O, et al. Spectral hole burning and its application in microwave photonics [J]. Nat Photo, 2017, 11: 36. doi: 10.1038/nphoton.2016.225 [2] Vitanov N V, Rangelov A A, Shore B W, et al. Stimulated Raman adiabatic passage in physics, chemistry, and beyond [J]. Rev Mod Phys, 2017, 89: 015006. doi: 10.1103/RevModPhys.89.015006 [3] Du Lei, Zhang Yan, Fan Chu-Hui, et al. Enhanced nonlinear characteristics with the assistance of a PT-symmetric trimer system [J]. Scientific Reports, 2018, 8: 2933. doi: 10.1038/s41598-018-21137-y [4] Du Lei, Liu Yimou, Jiang Bo, et al. All-optical photon switching, router and amplifier using a passive-active optomechanical system [J]. EPL, 2018, 122: 24001. doi: 10.1209/0295-5075/122/24001 [5] Bao Qianqian, Zhang Yan, Cui Cuili, et al. Dynamic generation and coherent control of beating stationary light pulses by a microwave coupling field in five-level cold atoms [J]. Optics Communications, 2018, 412: 49-54. doi: 10.1016/j.optcom.2017.11.081 [6] Zhang Yan, Liu Yimou, Tian Xuedong, et al. Tunable high-order photonic band gaps of ultraviolet light in cold atoms [J]. Physical Review A, 2015, 91: 013826. doi: 10.1103/PhysRevA.91.013826 [7] Zhang Yan, Liu Yimou, Zheng Taiyu, et al. Light reflector, amplifier, and splitter based on gain-assisted photonic band gaps [J]. Physical Review A, 2016, 94: 013836. doi: 10.1103/PhysRevA.94.013836 [8] Hsiao Ya-Fen, Tsai Pin-Ju, Chen Hung-Shiue, et al. Highly efficient coherent optical memory based on electromagnetically induced transparency [J]. Phys Rev Lett, 2018, 120: 183602. doi: 10.1103/PhysRevLett.120.183602 [9] Bhattarai M, Bharti V, Natarajan V. Tuning of the Hanle effect from EIT to EIA using spatially separated probe and control beams [J]. Sci Rep, 2018, 8: 7525. doi: 10.1038/s41598-018-25832-8 [10] Tian Xingxia, Li Dongkang, Wu Jinhui. Coherent induced hole-burnings in a Doppler broadened four-level atomic system [J]. Opt Comm, 2010, 283: 2561. doi: 10.1016/j.optcom.2010.02.022