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驻波场驱动的热原子系统量子相干效应的研究

Quantum Coherence Driven by a Standing Wave in Hot Atomic Systems

【作者】 陈卓人

【导师】 苏雪梅;

【作者基本信息】 吉林大学 , 光学, 2014, 博士

【摘要】 本论文主要研究了强耦合场作用下的原子相干效应。在行波场或者驻波场形式的强耦合场作用下,相干介质的光学性质发生了改变。我们回顾了一些原子相干效应的发展历史,并着重讨论了电磁感应光透明和光子带隙现象。本论文包括了三部分创新性内容:首先,我们分析了三能级Cs原子Λ型和梯型不对称电磁感应光透明和光子带隙谱线,通过理论分析,我们得到了缀饰态处的不对称吸收率谱线。然后,我们实验上得到了二能级原子系统中在两种不同形式的驻波场作用下的光子带隙现象,并对得到的探测场透过谱与反射谱中出现一条主带隙和两条次带隙的现象进行了分析。最后,我们提出了一种以热Rb原子五能级模型,用一个可调谐的驻波场控制多波混频过程,实现三窗口电磁感应双光子带隙效应和双光子电磁感应光透明效应。在两个双光子共振条件下,我们在三个探测场的共振频率处得到了电磁感应三光子带隙,当令其中一个探测场频率增强作为第二耦合场,得到三窗口双光子过滤和三窗口的双光子电磁感应光透明效应。本论文主要内容包括:1我们提出两种五能级模型系统来解释实验中测得的具有不对称谱线形状的电磁感应光透明和光子带隙现象。我们发现目前许多热原子三能级Λ模型和ladder模型的实验谱线具有不对称性,但关于这些实验的理论拟合或预言的探测场的吸收与色散谱却是对称的。我们在简化的热Cs原子三能级Λ模型和ladder模型的基础上,考虑了附加在Λ模型上面的能级和ladder模型的中间能级上的两个临近的能级的作用,来分析实验上产生不对称谱线形状物理机制。根据实验所选择的能级,我们发现这两个临近能级中的一条可能在耦合场的作用下跃迁,这个可以跃迁的能级与原始的三能级系统中的另外两个能级组成了一个三能级系统,这个新的三能级系统中,耦合场的失谐不为0,探测场的透过谱线是不对称的。因此,与原始的三能级系统中探测场对称的透过谱线叠加之后,在这个新的三能级系统与原始的三能级系统的共同作用下,我们理论得到了不对称的电磁感应光透明和光子带隙,理论计算与已有的实验现象一致。同时,我们考虑了热原子的多普勒非均匀加宽的作用,求解出密度矩阵方程。我们提出的五能级系统对于分析在缀饰劈裂态处不对称透过谱的现象是一个简化的模型,并且可以推广到其他更远处的临近能级的作用。我们的理论很好的解释了具有不对称谱线的实验现象。2我们采用驻波场作为耦合场来实验观测二能级热Cs原子系统的电磁感应光子带隙现象。实验发现二能级系统的透过谱和反射谱中出现了一个主带和两个边带的情况。我们给出了出现这种情况的物理解释。考虑到热原子中的原子运动满足麦克斯韦速率分布,我们采用了傅立叶变换解密度矩阵方程的方法来拟合实验结果。我们通过分析驻波场中与探测场同向传播与反向传播分量对探测场透过率和反射率的贡献,定性分析了实验谱线的性质的基础上,进行了定量求解。我们发现在谱线共振点(p0)处存在一个主光子带隙之外,在主带的两侧对称的产生两个次带隙。当选择耦合场模式为不对称驻波场(>)时,加载在-z方向上的耦合场功率越低,主带隙的透射率和反射率越小,两个次带隙逐渐地向着主带隙移动。当反向拉比频率足够小的时候,次带隙最终消失。当选择第二种不对称驻波场耦合模式时,即拉比频率<,加载在+z方向上的耦合场功率越低,主带隙的透射率越大,而反射率越小。两个次带隙仍旧逐渐地向着主带隙移动直至完全消失。数值拟合很好的解释了实验观测的电磁感应光子带隙的性质。3我们运用一个可调谐的驻波场,诱导非均匀加宽Rb原子五能级结构中的双光子耦合效应。三个探测场在两个双光子共振条件下,用一个驻波场诱导量子相干效应,我们在共振频率处得到了电磁感应三光子带隙效应;用一个行波场来代替原来的驻波耦合场时,我们得到了三光子电磁感应光透明效应。选择三个探测场中的一个作为除了驻波场之外的第二个耦合场的情况下,两个缀饰能级劈裂成四个缀饰能级,在使另外两个探测场保持双光子共振的条件下,我们得到了三窗口的双光子共振滤波现象或三窗口的双光子电磁感应光透明效应。同时为了证明探测场的色散补偿效应,我们计算了介质输出端高斯波包的相移。

【Abstract】 This thesis for doctorate focuses on the effects of quantum coherence andinterference with a strong coupling field (either a traveling or standing wave field)because the optical properties of an interaction medium can be modified andcontrollable. We generalized the development of atomic coherence effects,especially on phenomena of electromagnetically induced transparency andphotonic band gap. The creative points in this thesis consist of three parts: Firstly,we propose a five-level system to analyze asymmetrical transmitted spectra ofprobe field in traditional three-level Λ-type and ladder-type systems forElectromagnetically induced transparency and photonic band-gap in hot Cs atoms.By controlling the parameters, the asymmetrical absorptions at dressed states areobtained. Secondly, we carried out the experimental observation and theoreticalanalyzing electromagnetically induced photonic bandgaps in two-level systemwith a strong symmetric and two types of asymmetric standing wave (SW) drivingfield. One main band and two sidebands are measured for the transmitted andreflected spectra. Finally, we propose a scheme by applying a tunablestanding-wave (SW) to control various multi-wave mixing processes in a hotfive-level Rb atomic system to realize triple two-photon photonic bandgaps orthree EITT windows. In two two-photon resonant conditions, electromagneticallyinduced triple-photonic bandgaps can be formed at three resonant frequencies ofthree traveling-wave (TW) probe fields. While one probe travelling-wave (TW)field is as strong as the standing-wave field to be a coupling field, triple-bandpasstwo-photon filters or three EITT windows can be obtained.The contents are mainly divided as three parts: 1. We propose two five-level systems to analyze asymmetrical transmittedspectra of probe field in traditional three-level Λ-type and ladder-type systemsfor Electromagnetically induced transparency and photonic band-gap in atomswith a strong coupling field. It is found that many previous theoreticalcalculations for EIT and EIG provide symmetrical transmission at dressedsplitting states with resonant coupling field, but experimental observationsproduced asymmetrical shapes. Here two five-level systems where two additionaladjoining levels close to the middle level in ladder system or upper level in Λsystem are utilized to analyze asymmetrical spectra shapes in experimentalobservations for EIT and photonic band gap in thermal Cs atoms, respectively.Based on the energy levels for experiments, we found that the two neighboringlevels are chosen to satisfy that transitions of the coupling laser to one of the twois inhibited and to the other is admitted. The reasons of asymmetry transmission atdressed splitting states are found to be the asymmetry transmission in three-levelsystem formed by the admitted neighboring level and the two other levels inoriginal three-level system where it is none zero for the frequency detuning of thecoupling field with corresponding transition to the admitted neighboring level. Wesolve density matrix equations for steady-state solutions without the supposingthat all populations are on the ground state as treatment previously in Dopplerinhomogeneous broadenings for hot atoms. The theoretical calculation shows thatinfluence of other further neighboring levels are the same as the two adjoininglevels. The five level systems are the simplest ones to analyze symmetryproperties of transmissions at dressed splitting states. Our simulating results areconformably to the realistic observations.2. We observed and simulated the effects of quantum coherence driven by aSW field in a thermal two-level Cs atomic system. One main band and twosidebands are measured for the transmitted and reflected spectra. We carry outphysical interpretation about the observations in SW-dressed atom picture and employ method of Fourier transformation to solve density-matrix equations forhot two-level system to simulate the experimental results. We analyze thecontribution of co-and counter-propagating coupling components of SW to thetransmission and reflection spectra. The measured optical spectra exhibit theproperties:(1) there exists a main photonic bandgap at resonance (p0) andtwo sidebands located symmetrically around the main band;(2) with the first typeof asymmetric SW (>) drive, the lower powers in–z direction, the smallertransmission and reflection at main bands; the two subbands move towards themain band and finally disappear when much smaller is used and similarphenomena are measured as EIA by a copropagating TW;(3) with the secondtype of asymmetric SW (<) drive, the lower the powers in+z direction, thelarger transmissions and lower reflections at main band; the two subbands stillmove towards the main band and disappear gradually. The simulation results arefound to be consistent with the experimental results.3we use a tunable standing-wave field to induce two-photon coherence effects inan inhomogeneous five-level Rb atomic vapor. It is demonstrated that tripleprobe-photon bandgaps can be induced by quantum coherence effects of thestanding-wave under two-photon resonant conditions for the three probe fields.When the standing-wave field is changed to a traveling wave field, triple-photonelectromagnetically induced transparency phenomena are obtained under the sameconditions for the three probe fields. When one of the three probe field keepsresonance as a second coupling field besides the tunable standing-wave field, twodressed states further split into four dressed states. By keeping two-photonresonance of the other two probes, triple-bandpass two-photon filters can beobtained. Triple EITT (electromagnetically induced tow-photon transparency)windows are obtained if a traveling field replaces the standing wave. Phase shiftsof probe pulses with Gaussian shapes entering at one end of the medium are calculated to show the scheme useful for dispersion compensation for the probesignals.

  • 【网络出版投稿人】 吉林大学
  • 【网络出版年期】2014年 09期
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