太赫兹场中里德堡铷原子的相干操控

采用含时多态展开方法研究了太赫兹场中里德堡铷原子布居数迁移的动力学过程,计算了一个太赫兹脉冲序列与三能级里德堡铷原子系统相互作用后的布居数分布,以及多脉冲序列对多量子态里德堡铷原子系统的相干操控,给出了同一主量子数n中不同角量子数l态布居数的含时演化过程.结果表明:通过优化太赫兹脉冲序列参数,铷原子布居数可由初态被抽运到较高的目标态,在太赫兹频率范围实现里德堡原子的操纵与控制.     

高斯型微波脉冲强度和半宽对里德堡钾原子相干跃迁布居的影响

利用含时多态展开方法(the time-dependent multilevel approach, TDML）,计算了脉冲强度及半宽对里德堡钾原子相干跃迁布居数的影响。结果表明,脉冲强度的单纯增加并不能在本质上提高目标态布居数的迁移率。 在脉冲强度及半宽双因素共同作用下,单色激光驱动里德堡钾原子相干激发时,目标态的跃迁几率仅取决于脉冲的强度和半宽乘积。     

高斯型微波脉冲强度和半宽对里德堡钾原子相干跃迁布居的影响

利用含时多态展开方法(the time-dependent multilevel approach, TDML）,计算了脉冲强度及半宽对里德堡钾原子相干跃迁布居数的影响。结果表明,脉冲强度的单纯增加并不能在本质上提高目标态布居数的迁移率。 在脉冲强度及半宽双因素共同作用下,单色激光驱动里德堡钾原子相干激发时,目标态的跃迁几率仅取决于脉冲的强度和半宽乘积。     

静电场中铷原子里德堡态反交叉位置和宽度的计算

用碱金属原子的模型势结合B-样条函数展开方法研究了静电场中铷原子里德堡态的能级结构特点,计算了铷原子主量子数n由16到25之间的(n 3)s和(n,k)态间的Stark能级反交叉位置和宽度,得到了与实验相一致的结果,并给出了计算铷原子在静电场中高里德堡态能级反交叉位置的经验公式.     

频率啁啾激光场中锂原子的激发与态囚禁

采用含时多态展开方法,对不同频率啁啾激光场中里德堡锂原子布居数的相干迁移特性进行了计算研究。结果表明：布居数跃迁几率对激光脉冲形状、激光场强度、啁啾率等参数非常敏感,在合适的激光参数下,可以实现布居数在四个量子态之间的完全迁移和量子态的囚禁。     

室温铯原子气室窄线宽相干布居振荡光谱

相干布居振荡(coherent population oscillations, CPO)光谱是一种原子布居数调制光谱,主要利用两束位相锁定、频率差小于原子自发辐射线宽的耦合光和探测光与原子相互作用,激光强度调制会导致原子布居数相干振荡,实现窄带宽的探测光透射.本文基于L型原子能级结构,在室温铯原子系综中实现了相干布居振荡光谱,光谱典型线宽小于50 kHz,远低于5.2 MHz的自发辐射线宽. L型能级结构的相干布居振荡光谱线宽依赖多个简并能级系统的布居数关联振荡,其不要求原子态的相位关联,有利于在长激发态寿命的Rydberg原子系统中基于相干布居振荡获得窄线宽光谱,从而提高基于Rydberg原子光谱的精密测量的灵敏度.     

里德堡(Rydberg)原子

“里德堡原子”在文献中出现,只是近四、五年的事。随着原子物理理论与实验手段的进一步发展,对里德堡原子的研究越来越引起人们的注意,它已成为原子物理学一个必不可少的分支。 一、里德堡原子的结构和能级 原子体系的能量其主要部分是由主量子数n决定的(无论是简并或非简并情况)。高激发态原子,就称做里德堡原子。它的主量子数n,高达几十以至上百。自然界中处于这样高的激发态原子数目不多,主量子数n一般是几十。 对于处在高激发状态的氢原子即里德堡氢原子,玻尔(Bohr)氢原子模型给出了一个很好的近似。虽然这时主量子数n很大,原子核外部…     

多光子过程中相位退相干时两原子布局数反转

利用全量子理论的方法,研究了存在相位退相干时多光子T-C模型中两个二能级原子与二项式光场相互作用系统中两原子的布居数反转。讨论了相位退相干系数、二项式光场系数、最大光子数、跃迁光子数对原子布居数反转的影响。结果表明：相位退相干减少了原子布居数反转的振幅、破坏了原子的量子特性。改变跃迁光子数,可以改变原子间布居数反转演化周期及演化强度。当二项式光场的最大光子数增大时,原子布居差的崩塌-回复现象就会逐渐消失。相位退相干因子不变时, 二项式光场从相干态过渡到数态过程中,原子布居的振荡频率由大变小,周期性的崩塌与回复现象逐渐消失。     

ns6s里德堡分子的势能曲线

里德堡电子与基态原子的低能电子散射形成长程里德堡分子,这种分子具有大的轨道半径,丰富的振动能级和永久电偶极矩等特点。本文考虑铯里德堡ns态与(n-4)l(n为主量子数,l为角量子数且l2)近简并态的非绝热耦合与p-波共振现象,数值计算了长程铯里德堡分子的势能曲线。分析ns6s(n=32-36)态分子最外层势阱,研究了长程里德堡分子的势阱深度、平衡距离与主量子数n的关系,为实验研究长程里德堡分子提供理论依据。     

多光子过程中相位退相干时两原子布局数反转

利用全量子理论的方法,研究了存在相位退相干时多光子T-C模型中两个二能级原子与二项式光场相互作用系统中两原子的布居数反转。讨论了相位退相干系数、二项式光场系数、最大光子数、跃迁光子数对原子布居数反转的影响。结果表明：相位退相干减少了原子布居数反转的振幅、破坏了原子的量子特性。改变跃迁光子数,可以改变原子间布居数反转演化周期及演化强度。当二项式光场的最大光子数增大时,原子布居差的崩塌-回复现象就会逐渐消失。相位退相干因子不变时, 二项式光场从相干态过渡到数态过程中,原子布居的振荡频率由大变小,周期性的崩塌与回复现象逐渐消失。     

Laser pulse design for coherent control of Rydberg lithium atoms

<正>Using the time-dependent multilevel approach(TDML),this paper studies the dynamics of coherent control of Rydberg lithium atoms and demonstrates that Rydberg lithium atoms can be transferred to states of higher principal quantum number by exposing them to specially designed frequency-chirped laser pulses.The population transfer from n= 70 to n= 75 states of lithium atoms with efficiency of more than 90%is achieved by means of the sequential adiabatic rapid passages.The results agree well with the experimental ones and show that the coherent control of the population transfer from the lower n to the higher n states can be accomplished by the optimization of the chirping parameters and the intensity of laser field.     

Coherent excitation of Rydberg atoms in an ultracold gas

We demonstrate two schemes for the coherent excitation of Rydberg atoms in an ultracold gas of rubidium atoms employing the three-level ladder system 5S_1/2-5P_3/2-n?_j. In the first approach rapid adiabatic passage with pulsed laser fields yields Rydberg excitation probabilities of 90% in the center of the laser focus. In a second experiment two-photon Rydberg excitation with continuous-wave fields is applied which results in Rabi oscillations between the ground and Rydberg state. The experiments represent a prerequisite for the control of interactions in ultracold Rydberg gases and the application of ultracold Rydberg gases for quantum information processing.     

里德伯钠原子经绝热快速通道的布居数跃迁相干控制

运用含时多态展开方法和B-样条函数研究了啁啾频率微波场中里德伯钠原子的量子态之间的布居数迁移.计算了里德伯钠原子n=70-77的开普勒频率.计算了在不同的微波场中六个态的布居数从n=70到n=77随时间的迁移,布居数跃迁到最终态n=77达到了98%,这可以通过连续的单光子跃迁来实现.结果表明,通过优化微波脉冲参数可以实现从低态到较高态的布居跃迁的相干控制.     

Ionization and population transfer in lithium Rydberg states with ultrashort chirped laser pulses

We present a theoretical study of dynamics of Rydberg states of lithium using ultra short chirped laser pulse having a Gaussian envelope. The population transfer probabilities are calculated of different Rydberg states on chirped laser factors. The calculations are performed by direct numerical integration of Schr?dinger equation using fourth order Runge-Kutta method. The behavior of dynamics of Rydberg states for these factors is of great significance. These results are of potential interest in coherent quantum control, quantum computation and in many physical and chemical processes.     

Probing electronic coherence in a gas of dipole-dipole coupled Rydberg atoms

We demonstrate a novel time-domain method to probe electronic coherence in ensembles of cold Rydberg atoms coupled via nearly resonant dipole-dipole interactions. Short laser pulses create coherent superpositions of few-electron eigenstates which evolve under the influence of pulsed electric fields. The pulses steer the dynamics, enhancing the probability for finding atoms in np, rather than initially excited ns states. The enhancement reflects the underlying electronic coherence which persists for >10 μs, 2?orders of magnitude longer than previously measured dephasing times in the same system. Simulations suggest that atom motion is responsible for the eventual decoherence.     

Coherent transients in the femtosecond photoassociation of ultracold molecules

We demonstrate the photoassociation of ultracold rubidium dimers using coherent femtosecond pulses. Starting from a cloud of ultracold rubidium atoms, electronically excited rubidium molecules are formed with shaped photoassociation pump pulses. The excited state molecules are projected with a time-delayed probe pulse onto molecular ion states which are detected in a mass spectrometer. Coherent transient oscillations of the excited state population are observed in the wings of the pump pulse, in agreement with the time-dependent solution of the Schr?dinger equation of the excitation process.     

The dynamics of a THz Rydberg wavepacket

An optically excited Rydberg wavepacket can be generated by exciting the electron from a low-lying state to a coherent superposition of high-lying states with a short broadband optical pulse. A special kind of Rydberg wavepacket is generated in the case of a interaction of a weak THz half cycle pulse with a stationary Rydberg state, called the THz wavepacket. This THz wavepacket is a coherent superposition of the initial Rydberg state and its neighbouring states. We have investigated the time evolution of THz wavepackets by measuring the impact of two in time delayed half cycle pulses ( ≈ 200 V cm^-1) on the population of a stationary (n = 40) Rydberg state in rubidium. The first half cycle pulse creates the THz wavepacket and the second half cycle pulse probes the dynamics of the THz wavepacket. We support our experimental data by numerically solving the Schr?dinger equation and with a semi-classical picture. Whereas an optically excited wavepacket is initially localized, a THz wavepacket is initially delocalized and becomes localized after half a revival time. Received 23 August 2000 and Received in final form 27 March 2001     

A laser system for the excitation of rubidium Rydberg states using second harmonic generation in a PPLN waveguide crystal

We report on a laser system at a wavelength of 495 nm which is suitable for the excitations of low lying Rydberg states of rubidium atoms. The system is based on frequency doubling of a seeded diode laser in a periodically poled waveguide crystal. We achieve an output power of up to 35 mW and prove the single-frequency performance by direct two photon laser spectroscopy of the rubidium 14D _5/2 and 14D _3/2 states. The measured fine structure splitting is consistent with quantum defect theory calculations.     

Matter-wave interferometry with atoms in high Rydberg states

Matter-wave interferometry has been performed with helium atoms in high Rydberg states. In the experiments the atoms were prepared in coherent superpositions of Rydberg states with different electric dipole moments. Upon the application of an inhomogeneous electric field, the different forces on these internal state components resulted in the generation of coherent superpositions of momentum states. Using a sequence of microwave and electric field gradient pulses the internal Rydberg states were entangled with the momentum states associated with the external motion of these matter waves. Under these conditions matter-wave interference was observed by monitoring the populations of the Rydberg states as the magnitudes and durations of the pulsed electric field gradients were adjusted. The results of the experiments have been compared to, and are in excellent quantitative agreement with, matter-wave interference patterns calculated for the corresponding pulse sequences. For the Rydberg states used, the spatial extent of the Rydberg electron wavefunction was ～320?nm. Matter-wave interferometry with such giant atoms is of interest in the exploration of the boundary between quantum and classical mechanics. The results presented also open new possibilities for measurements of the acceleration of Rydberg positronium or antihydrogen atoms in the Earth's gravitational field.