共查询到20条相似文献,搜索用时 96 毫秒
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研究了双势阱玻色-爱因斯坦凝聚体系(BEC)的自俘获现象(self-trapping). 在平均场近似下通过相平面(phase space)分析的方法研究了两种自俘获的机理:1)势阱中的粒子数在平衡位置附近振动,而相对相位随时间单调变化(running-phase); 2) 势阱中的粒子数和相对相位都在平衡点附近振动. 研究了周期调制场对自俘获现象的影响,发现发生自俘获现象的相变参数能够被周期场非常有效的调制,从而在弱相互作用BEC体系中也可以观察到自俘获现象. 还研究了多体量子涨落对自俘获现象的影响,讨论了在现有的实验条件下对凝聚体自俘获现象进行观察和周期调制.
关键词:
玻色-爱因斯坦凝聚
自俘获
双势阱
周期调制 相似文献
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Bell态原子与双模纠缠相干光场相互作用系统的原子布居数演化 总被引:3,自引:1,他引:3
运用全量子理论并结合数值计算方法,研究了处于Bell态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的原子布居数演化特性.讨论了双原子体系的初态、光场的平均光子数、双模纠缠相干光场的纠缠程度以及双原子体系的原子间耦合强度对原子布居时间演化的影响.结果表明:双原子体系的初态为|β11〉时,原子布居数不随时间变化;初态为|β00〉、|β01〉和|β10〉时,当初始平均光子数增大到一定数值时演化特性呈现出周期性的崩塌和回复效应,随初始光子数的增加时间演化曲线的振荡频率增大振幅减小,且初态为|β00〉或|β10〉时原子布居的回复周期是初态为时|β01〉的两倍;双模纠缠相干光场的纠缠程度以及原子间偶极相互作用的强弱对Rabi振荡频率没有影响但对振幅有着显著的影响. 相似文献
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本文利用一个具有隧穿耦合效应的四能级结构模型来描述超冷铯原子制备超冷铯分子的过程,理论分析了受激拉曼绝热通道过程中的两激光脉冲参数对铯原子-分子转换效率的影响。结果表明,在原子-分子暗态条件下,通过双色光缔合利用双光子共振条件的最优化处理方法可以使转换效率提高到90%以上,并给出了两激光脉冲参数的最优化区间。另外,通过分析原子态和束缚分子基态上粒子数布居的动力学演化,给出了光场的最优化条件,只有适当的匹配两激光场的有效Rabi频率、延迟系数和脉冲宽度时,才能高效地实现超冷铯原子-分子的相干布居转换。 相似文献
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在平均场理论和两模近似下,通过观察布居数差随时间的演化, 以及布居数差的平均随非线性相互作用参数的变化, 研究了对称双势阱以及势阱间高频调制时Fermi超流气体在unitarity区域和Bose-Einstein凝聚区域的自俘获现象. 给出了出现自俘获现象的边界条件;发现高频调制在一定调制范围内使自俘获现象更容易实现. 最后研究了初值对自俘获的影响, 发现初值的绝对值|s(0)|的增加更有利于自俘获的实现. 相似文献
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当一个单独的分子被镶嵌在一个主体的媒质中时,外加的激光场可以使其中的隧道效应被抑制.外场作用时,形成A型三能级系统,通过缀饰分析法、黑态明态分析法和一些近似,得出结论.明黑态的分析乃是对这一特殊系统发生相干隧穿抑制现象的一种物理解释.在一定的情况下粒子不但可以被定域在各自所处的阱里,而且可以完全定域在较低的势阱里. 相似文献
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在平均场理论和两模近似下,通过观察布居数差随时间的演化,以及布居数差的平均随非线性相互作用参数的变化,研究了对称双势阱以及势阱问高频调制时Fermi超流气体在unitarity区域和Bose-Einstein凝聚区域的自俘获现象.给出了出现自俘获现象的边界条件;发现高频调制在一定调制范围内使自俘获现象更容易实现.最后研究了初值对自俘获的影响,发现初值的绝对值︳s(O)︳的增加更有利于自俘获的实现. 相似文献
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Coherent population trapping is shown to occur in a driven symmetric double-well potential in the strong-field regime. The system parameters have been chosen to reproduce the 0(-) <--> 3(+) transition of the inversion mode of the ammonia molecule. For a molecule initially prepared in its lower doublet we find that, under certain circumstances, the 3(+) level remains unpopulated, and this occurs in spite of the fact that the laser field is resonant with the 0(-) <--> 3(+) transition and intense enough so as to strongly mix the 0(+) and 0(-) ground states. This counterintuitive result constitutes a coherent population trapping phenomenon of nonperturbative origin which cannot be accounted for with the usual models. 相似文献
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Power-law-distributed dark states are the main pathway for photobleaching of single organic molecules 总被引:1,自引:0,他引:1
Hoogenboom JP van Dijk EM Hernando J van Hulst NF García-Parajó MF 《Physical review letters》2005,95(9):097401
We exploit the strong excitonic coupling in a superradiant trimer molecule to distinguish between long-lived collective dark states and photobleaching events. The population and depopulation kinetics of the dark states in a single molecule follow power-law statistics over 5 orders of magnitude in time. This result is consistent with the formation of a radical unit via electron tunneling to a time-varying distribution of trapping sites in the surrounding polymer matrix. We furthermore demonstrate that this radicalization process forms the dominant pathway for molecular photobleaching. 相似文献
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Details of the process of the interstitial trapping by substitutional He impurity in the b.c.c. -Fe crystal were investigated by a computer simulation method. It was found that the trapping region which includes 24 atom places surrounding the impurity was anysotropic and stretched along the close-packed direction. In the trapping process the self-interstitial atom substitutes He atom. In this case He is replaced and produced a stable static crowdion along the 〈100〉 direction. The binding energy of such a configuration is positive and equal to 1,67 ev. 相似文献
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K. S. Gochelashvili A. V. Dem’yanov O. N. Evdokimova I. V. Kochetov G. F. Makarenko 《Bulletin of the Lebedev Physics Institute》2013,40(6):137-144
A self-consistent numerical model for the self-sustained high-current pulsed discharge is constructed based on the solution of the equations of the population of H2 electronic and vibrational states. The model accounts for electronic, ion-molecular, and vibrational kinetics, electron attachment to and detachment from the H2 molecule, Lyman and Werner band emission, and their radiation trapping. The equations of electron-vibrational kinetics are solved simultaneously with the Boltzmann equation for the electron energy distribution function and the external electrical circuit equations. 相似文献
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Dependence of charge trapping of fluorescent and phosphorescent dopants in organic light-emitting diodes on the dye species and current density 下载免费PDF全文
This paper utilizes multilayer organic light-emitting
diodes with a thin layer of dye molecules to study the mechanism of
charge trapping under different electric regimes. It demonstrates
that the carrier trapping was independent of the current density in
devices using fluorescent material as the emitting molecule while this
process was exactly opposite when phosphorescent material was used.
The triplet--triplet annihilation and dissociation of excitons into
free charge carriers was considered to contribute to the decrease in
phosphorescent emission under high electric fields. Moreover, the
fluorescent dye molecule with a lower energy gap and ionized
potential than the host emitter was observed to facilitate the
carrier trapping mechanism, and it would produce photon emission. 相似文献
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T. Ya. Karagodova 《Optics and Spectroscopy》2005,98(6):805-810
Specific features of the coherent population trapping effect are considered in the generalized Λ system whose lower levels are the magnetic sublevels of the fine structure levels of the thallium atom. Numerical experiments were performed aimed at examination of the coherent population trapping for the case of nontrivial, but feasible, initial populations of the upper metastable fine structure level. Such populations may be obtained, for example, due to the photodissociation of TlBr molecules. The possibility of reducing the number of resonances of the coherent population trapping in a multilevel system, which may be useful for high-resolution spectroscopy, is demonstrated. It is shown that the magnitude and shape of the resonances can be controlled by varying the orientation of the polarization vectors of the light field components with respect to each other and to a magnetic field. In addition, studying the shape of the coherent population trapping resonances for the atoms obtained by photodissociation of molecules may provide information about these molecules. 相似文献
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研究了少周期脉冲串作用下三能级原子中的布居转移和相干布居捕获现象.在非旋波近似的情况下求解了密度矩阵方程.研究结果表明在等时间间隔的锁相脉冲作用下,系统能级的布居逐步转移并积累,系统基态相干也逐步积累.在满足脉冲重复频率为基态能级频差的整数分之一倍时,三能级系统和频率梳中两梳齿频率成分作用形成相干布居捕获现象,原子暗态布居值达到最大,介质对脉冲透明.在适当选取少周期脉冲参量的情况下,在0.5个ns的时间内三能级系统相干性演化到最大后到达稳态,相干布居捕获发生.与脉宽为100个fs的多周期脉冲相比,少周期脉冲串在介质中建立相干布居捕获的时间缩短两个数量级.由于频率梳中与三能级系统发生作用的梳频成份有相同的频移,相干布居捕获的条件双光子共振仍然满足.因而,当两基态能级频率差较大时,如果选取少周期脉冲载波频率为系统能级1至2和1至3的传输频率之和的一半ω=(ω1+ω2)/2,室温下原子热运动的引起的多普勒频移并不会破坏相干布居捕获. 相似文献
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根据Holstein的共振辐射俘获理论,讨论了气体温度和辐射俘获下能级粒子数密度对辐射俘获上能级有效辐射寿命的影响,显示辐射俘获下能级粒子数密度是辐射俘获效应中的主导因素.计算了钙,锶,钡和汞四种离子七条共振-亚稳能级跃迁激光在不同电离率下产生共振辐射俘获效应的阈值条件,发现当电离率为5%时这类激光的出光温度与共振辐射俘获的阈值温度相一致,这与实验得出的电离率为3%—5%相符合.表明达到共振辐射俘获阈值条件是该类激光实现粒子数反转的重要因素. 相似文献