HeH+体系光缔合反应的动力学研究

采用含时量子波包方法研究基电子态HeH⁺体系优化的光缔合几率,即He+H⁺→HeH⁺随碰撞粒子对初始动量的变化,并研究伴随该过程的多光子跃迁和解离.选取v=6振动能级为目标态,通过优化激光场参数得到碰撞粒子对的最优光缔合几率.结果表明：随着碰撞粒子对初始动量的增加,光缔合所用的最优激光场的持续时间逐渐减少,但光场的强度和失谐逐渐增加.在某些初始碰撞动量附近,由于共振多光子跃迁过程的存在,最优的光场不能严格地将碰撞粒子对缔合到目标态.此外,研究表明随着初始动量的增加,系统的超阈值解离几率近似线性地增加到一个最大值,直至饱和强度.并且,在碰撞粒子对的初始动量较大时,超阈值解离主导解离过程.     

NO2分子内能传递和弛豫过程的光声和荧光光谱探测

将荧光光谱和光声光谱两种互补的探测技术结合起来,从辐射和无辐射跃迁两个方面,分析了 532nm激光作用下,NO2分子的激发和弛豫过程.发现NO2分子在激光作用下,将跃迁至第一激发电子态.当样品气压较低时,受激NO2分子除辐射荧光外,可通过快速的内能转移过程实现在几个振转能级的再布居;随样品气压的升高,分子间碰撞加剧,受激NO2分子通过分子间的碰撞,实现在多个振转能级的再布居.激光布居能级的荧光辐射效率随样品气压的升高逐渐降低,而长波区域的荧光辐射及光声信号强度逐渐增强,说明在高样品气压条件下,受激NO2分子的弛豫过程除辐射荧光外,还存在很强的碰撞弛豫过程,在碰撞弛豫过程中受激NO2分子将振动能转化为热运动的平动能,引起温度升高而产生很强的声信号.     

超低频调制光缔合光谱的实验研究

通过激光冷却技术在磁光阱中俘获原子数约107,温度约200 μK,直径约400 μm的超冷铯原子,利用超冷铯原子光缔合方法制备了激发态的超冷铯分子。实验研究了光缔合光不同扫描速率对铯分子振转光谱分辨率的影响,发现光缔合光扫描速率较慢时,铯分子振转光谱分辨率较高。通过高灵敏的雪崩光电探测器探测冷原子荧光,获得了超冷铯分子第一激发态6S_1/2+6P_3/2离解限0-_g长程态高分辨振转光谱。为了实现受控拉曼光缔合制备超冷基态分子,光缔合激光频率需要锁定在原子-分子共振跃迁线,对超冷原子光缔合光谱进行了超低频波长调制,通过改变调制幅度和调制频率获得最优化的一阶微分信号,将该信号反馈回激光器,实现闭合环路稳频,满足了受控拉曼光缔合制备振转能级可控的基态分子的实验要求,该工作对研究受限空间中的超冷原子分子具有很重要的意义。     

纠缠压缩真空态的纠缠转移

通过分析光学分束器对压缩真空态光场的作用,发现如果分束器的输入光是两束具有同样振幅和相位的单模压缩真空态光场,则输出光为双模压缩真空态光场;若分束器的输入光是两束具有同样振幅但有π相位差的单模压缩真空态光场,则输出光仍为两束单模压缩真空态光场.对于双模压缩真空态光场,每个模中容纳的光子数可以是基数或偶数.而对于单模压缩真空态光场,每个模中只能包含偶数个光子.根据这些结果,提出了一个纠缠转移的方案.在这个方案中,两个纠缠压缩真空态光场被用作量子信道,通过利用光学分束器作用和光子数探测的方法,并在经典通讯的帮助下,实现了三个通讯伙伴之间的纠缠转移.     

336—356nm波段CS2的多光子解离过程研究

测量了ＣＳ２分子在３３６￣３５６ｎｍ的ＲＥＭＰＩ分质量光谱。并通过比较母体离子和碎片离子的分质量光谱以及参照不同波长下的各向种离子在不同光强下的产率比,泽母体及碎片离子的生成机理进行了考察。发现在此波段范围内ＲＥＭＰＩ有两种不同的通道。一类是通过双光子跃迁至４ｓＲｙｄｂｅｒｇ态后,再吸收光子至超激发态,然后自电离生成各种了子（Ｃ＾＋离子降外）。另一类是单光子菜振跃迁至＾￣３ａＡ２态后通过电离－解离     

强光场下非共振双光子跃迁相干控制

利用飞秒激光脉冲相位整形技术,从理论和实验两方面,对强激光场下分子体系苝溶液中非共振双光子跃迁的相干控制进行了研究。通过对飞秒激光脉冲进行相位扫描和余弦相位调制,发现分子体系中非共振双光子的跃迁几率能够被削弱,但不能完全消除。分子体系中非共振双光子跃迁的相干控制受到激光光场的形状和分子吸收谱谱宽的影响;与原子体系相比,分子体系中非共振双光子跃迁相干控制的调制效率降低。     

NPS态光场与运动二能级原子相互作用系统的保真度

利用全量子理论计算方法,研究NPS态光场与运动二能级原子相互作用系统和光场保真度的时间演化规律,分析原子初态、最大光子数、光场参量、原子运动速度、场模结构参量和跃迁光子数对系统和光场保真度的影响.结果表明:最大光子数越大或光场参量越小,保真度平均值越低;原子运动速度或场模结构参量增大保真度变大,振荡频率加快;跃迁光子数增大时,保真度周期性或无规则振荡;当原子初态处于叠加态时系统和光场保真度最大,且振荡规律相同.     

利用基频与倍频脉冲控制扩展“ladder”式跃迁

利用含时量子波包动力学方法研究了两束基频与倍频脉冲控制下的扩展"ladder"式跃迁.通过基频与2倍频脉冲控制分子布居从|0,0态跃迁至|5,0与|5,2态;基频与3倍频脉冲控制分子布居从|0,0态跃迁至|5,3?与|6,2态.计算结果表明,利用两束基频与倍频脉冲,通过"ladder"式跃迁,可以得到近100%的布居跃迁概率.两束脉冲间的相对相位角影响分子的布居分布.当脉冲频率比为1:2时,布居以π为周期变化;当脉冲频率比为1:3时,布居以2π为周期变化.     

多光子T-C模型中场熵的演化

利用Tavis-Cummings模型研究了耦合二能级原子通过多光子跃迁与相干态光场相互作用系统中场熵的演化规律,讨论了原子间耦合强度和光场初始平均光子数的变化对场熵演化的影响。数值计算结果表明: 场熵的演化受原子间耦合强度和光场初始平均光子数的变化的影响.随光场初始平均光子数的增大,场熵平均值增大。     

HD~+分子的强场光解离动力学及其量子调控的理论研究

利用精确求解原子核与电子耦合运动的三维含时量子波包法,理论研究了HD~+分子在强激光场中的光解离动力学,并给出了量子调控HD~+分子光解离通道的理论方案.通过分析HD~+分子在不同的初始振动态和激光场强度下的光解离动力学过程及其解离核动能谱,得出了HD~+分子的光解离机理及其随激光场强度的变化规律.研究结果表明,利用激光场的强度可以实现HD~+分子光解离通道的量子调控.当激光场强度I_1=4.0×10~(13) W/cm~2时,HD~+分子的光解离主要是通过净单光子吸收解离和净双光子吸收解离;当激光场强度增大到I_2=2.0×10~(14) W/cm~2时,直接双光子吸收解离取代了净单光子吸收解离,净双光子吸收解离的比重也下降了.     

Population transfer via adiabatic passage in the Rydberg potassium atom

Using the time-dependent multilevel approach, we have calculated the coherent population transfer between the quantum states of potassium atom by a single frequency-chirped laser pulse. The result shows that a pair of sequential `broadband' frequency-chirped laser pulses can efficiently transfer population from the initial state of the ladder system to the target state. It is also found that the population can be efficiently transferred to a target state and trapped there by using an `intuitive' or a `counterintuitive' frequency sweep laser pulse in the case of `narrowband' frequency-chirped laser pulse. Our research shows that the complete population transfer is related to the pulse duration, chirp rate, and amplitude of the laser pulse.     

Coherent population transfer in Rydberg potassium atom by a single frequency-chirped laser pulse

By using the time-dependent multilevel approach, we have calculated the coherent population transfer among the quantum states of potassium atom by a single frequency-chirped laser pulse. The results show that the population can be efficiently transferred to a target state and be trapped there by using an `intuitive' or a `counter-intuitive' frequency sweep laser pulse in the case of `narrowband' frequency-chirped laser pulse. It is also found that a pair of sequential `broadband' frequency-chirped laser pulses can efficiently transfer population from one ground state of the \La atom to the other one.     

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。     

Stabilizing photoassociated Cs2 molecules by optimal control

We demonstrate theoretically that photoassociated molecules can be stabilized to deeply bound states. This process is achieved by transferring the population from the outer well to the inner well using the optimal control theory, the Cs 2 molecule is taken as an example. Numerical calculations show that weakly bound molecules formed in the outer well by a pump pulse can be compressed to the inner well via a vibrational level of the ground electronic state as an intermediary by an additionally optimized laser pulse. The positively chirped pulse can enhance the population of the target state. With a transform-limited dump pulse, nearly all the photoassociated molecules in the inner well of the excited electronic state can be transferred to the deeply vibrational level of the ground electronic state.     

两束重合脉冲控制下的振转态布居转移

利用两束频率比为1:3的重合脉冲控制分子振转态布居转移. 计算结果表明, 初始态|0,0>到目标态|3,1>的跃迁概率接近100%. 两束脉冲的相位可以控制跃迁概率. 当φ ₁ =1.68 π 时, 两束脉冲相互增强, 跃迁概率增加. 当φ ₁ =0.64π 时, 两束脉冲相互抵消, 跃迁概率降低. 第二束脉冲的场强对布居转移过程具有较大影响.     

Creation of cluster state of four ions in ion-trap system by individual addressing

The cluster state is a special, highly entangled quantum state that forms the universal resource, on which measurement-based quantum computation can be performed. In this study, a new scheme is presented for creating four-ions cluster state in ion-trap system. This scheme is based on resonant sideband excitation in which the population is transferred to target states by precise control of pulse area. Meanwhile, the scheme is consist of combination of elementary stages belonging to a universal set whereby cluster state has been created in five interaction stages by individually addressed ions with red- or blue-sideband resonance laser pulses. The paper studies the population transfer of the system by numerical solutions of the master equation, considering the effect of decoherence channels due to dissipation in the phonon modes. The presented scheme does not require control of the turn-off ratio and time delay among pulses.     

Coherent Control of Population Transfer in Li Atoms via Chirped Microwave Pulses

We demonstrate theoretically that Li atoms can be transferred to states of a lower principal quantum number by exposing them to a frequency chirped microwave pulse. The population transfer of Li atoms from the n = 75 state to n = 70 with more than 90% efficiency is achieved by means of the sequential single-photon △n = -1 transitions. The calculation fully utilizes all of the available orbital angular momentum l states for a given n, and the interference pattern and population evolution dynamics of individual l states are analyzed in detail. Using the time-dependent multilevel approach, we describe the process reasonably well as a sequence of adiabatic rapid passages.     

利用多光子跃迁控制基态HF分子布居转移

采用波包动力学方法研究了HF分子基电子态的多光子跃迁. 激光场由两束频率比为1:2的重合红外脉冲构成. 态|0,0>作为初始态, 态|4,0>与态|4,2>分别作为目标态. 计算结果表明, 通过选取不同的共振频率, 可以控制布居跃迁至不同的目标态. 两束脉冲间的初相位差可以控制布居转移概率. 当初相位差为π/2的偶数倍时, 布居转移概率为最大值. 当初相位差为π/2的奇数倍时, 布居转移概率为最小值. 初相位差对于态|4,0>的布居影响大于态|4,2>. 关键词： 多光子跃迁 初相位 布居转移 波包     

The 5V(OH) Overtone Transition of HDO

The absorption spectrum of HDO has been recorded by intracavity laser absorption spectroscopy in the 16 540-17 055 cm(-1) spectral region corresponding to the 5nu(3) band centered at 16 920 cm(-1). The (0 0 5) vibrational state is found to be mostly isolated from the nearby rovibrational states. The corresponding rovibrational transitions were analyzed and fitted in the frame of the effective rotational Hamiltonian model in Pade-Borel approximants form. The spectroscopic parameters retrieved from the fitting reproduce 100 of the 109 determined energy levels with the root-mean-square deviation of 0.0072 cm(-1), close to the experimental accuracy. From the integrated relative intensities of a- and b-type transitions, the angle between the transition moment and the OH bond is estimated to be 46.4 degrees. This value is consistent with an increasing tilt of the transition dipole moment, away from the OH bond, when the OH stretching is excited. The evolution of the orientation of the transition dipole moment versus the vibrational excitation is then compared for the OH and OD overtone bands. Copyright 2000 Academic Press.     

微波场中里德堡锂原子的高激发跃迁

运用含时多态展开方法研究微波场中里德堡锂原子高激发态的性质,得到锂原子在微波场中的跃迁几率,实现对量子态的操纵与控制。结果表明：选择合适的振幅、频率等参数,可以实现布居数在量子态之间的完全跃迁。