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 A atom to the other one.

Population transfer by femtosecond laser pulses in a ladder-type atomic system

The population transfer in a ladder-type atomic system driven by linearly polarized sech-shape femtosecond laser pulses is investigated by numerically solving Schr6dinger equation without including the rotating wave approximation （RWA）. It is shown that population transfer is mainly determined by the Rabi frequency （strength） of the driving laser field and the chirp rate, and that the ratio of the dipole moments and the pulse width also have a prominent effect on the population transfer. By choosing appropriate values of the above parameters, complete population transfer can be realized.

Laser pulse design for coherent control of Rydberg lithium atoms

Using 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 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.

Laser pulse design for coherent laser control of potassium atoms

In this paper, the dynamics of coherent laser control of potassium atoms is studied by using the time-dependent multilevel approach （TDMA）. The calculation results of population transfer are presented with different laser fields. The results show that the population can be transferred to target state completely by a specially designed laser field.

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.

Hamiltonian Reduction of Quantum Systems Controlled by Pulses

We explores Hamiltonian reduction in pulse-controlled finite-dimensional quantum systems with near-degenerate eigenstates. A quantum system with a non-degenerate ground state and several near-degenerate excited states is controlled by a short pulse, and the objective is to maximize the collective population on all excited states when we treat all of them as one level. Two cases of the systems are shown to be equivalent to effective two-level systems. When the pulse is weak, simple relations between the original systems and the reduced systems are obtained. When the pulse is strong, these relations are still available for pulses with only one frequency under the first-order approximation.

Numerical exploration of coherent excitation in three-level ladder systems

The technique of stimulated Raman adiabatic passage （STIRAP） is used to transfer potassium atoms from the 22p state to the 21p Rydberg state through the intermediate state 22s. The results show that complete population transfer is related to pulse duration and overlap, and occurs when the pulse duration and overlap have adequate values. At the same time, population trapping is also formed. Complete population transfer can also occurs when the two-photon resonance condition （△s = △p） is met.

Population transfer of sodium in a single analytical laser pulse

The population transfer of sodium in a single analytical laser pulse was studied in three models:two-level sodium,three-level sodium and many-level sodium.The effect of a third state on a two-level system was studied by investigating a ladder three-level system.Two effects were found in the vicinity of the resonance frequency.

Effect of Pulse Temporal Profile on Autler-Townes Splitting in Photoelectron Spectrum

The effect of pulse temporal profiles on the Autler-Townes （AT） splitting in photoelectron spectra is theoretically studied by employing the time-dependent wave packet method for a rotational Na2 molecule. The AT splitting which results from the sufficient Rabi oscillations is affected by the pulse profile and molecular alignment. The AT splitting may be observed only by utilizing proper pulse profiles with a certain intensity.

Coherent Single-Electron Transfer in Coupled Semiconductor Quantum Dots Driven by a Few-Cycle Pulse

We theoretically study the coherent transport of a single electron between the ground states of a double coupled quantum dot structure. The coherent transport is externally controlled by applying a few-cycle pulse with an adjustable carrier-envelope phase(CEP). By simulating numerically, it is shown that there exhibits a strong dependence of electron transport on the CEP and on the arrival time of few-cycle pulse. We provide a simple analytical description for this phenomenon by approximating the quantum dot structure as a three-level Λ-type system. These results also illustrate the potential of utilizing excitation in coupled quantum dots as a means of measuring the CEP of few-cycle pulses.

量子控制论在化学中的应用

控制量子现象是化学研究中的一个重要目标,量子控制论对实现该目标具有积极的指导意义。本文综述了量子控制论在化学中的应用及其进展,重点分析了量子相干控制、量子优化控制、闭环学习控制和能控性观念在化学研究中的应用,介绍了它们的研究现状,并对其未来研究进行了展望。

超短强激光场中双原子分子的振动布居转移

利用含时量子波包的方法从理论上研究了超短强激光场中双原子Na2分子的选择振动激发。改变激光脉冲的强度可以实现对分子振动激发的选择性控制。在较弱激光强度下,布居被激发到较高振动能级上;增强激光强度,布居则被转移到较低振动能级上。振动布居选择性激发可以用绝热光诱导势能面的概念解释。

在缀饰场中四能级“Ladder”系统的布局数转移(英文)

利用"反直觉"频率啁啾激光脉冲分析了偶能级ladder系统的布局数迁移,其中在缀饰激光场作用下N-2个中间态进行耦合.作为偶能级ladder系统的代表,我们着重分析了四能级ladder系统.研究发现如果缀饰激光场足够强且发生共振,则在能级1和能级4之间发生完全布局数迁移必须要求有一个恰当的脉冲叠加面积.调谐pump激光和stokes激光,使其中一个缀饰中间态发生共振,则可以使这个四能级系统简化为三能级系统.

量子系统的有效维数鉴别和约化理论

考虑在外界激光脉冲控制下的含近简并能级多能级系统的量子动力学,该多能级系统模型包括了一个基态和多个激发态,其中假设基态与各个激发态之间都存在跃迁。研究了不同激光脉冲场控制下的基态到近简并多能级激发态的布居转移。研究表明,在脉冲激光很短时,所考虑的多能级系统可以约化为一个二能级系统,并得到了在激光脉冲为多频弱场和单频强场时有效二能级系统参数的近似解析公式。以上结果可以推广到有多组近简并能级的多能级系统,用来鉴别有效控制维数,简化设计系统的控制策略。

基于脉冲整形的激发双重态间的相干布局操控

为了实现红外飞秒脉冲的整形及调控,采用4f系统相位控制技术,实验搭建了脉冲整形装置,并利用整形脉冲对铷原子体系中激发双重态间的相干布居转移进行操控。结果表明,控制抽运脉冲的附加相位,可实现双重态中上激发态的饱和布居,通过修改附加相位函数可将上、下激发态的布居数反转。整形脉冲同样适用于其它的原子和分子系统的相干布居转移的操控。

准Λ型四能级中用非匹配高斯脉冲实现相干布居转移

文章研究用非匹配高斯脉冲实现四能级准Λ型系统中的相干布居转移。从密度矩阵方程出发,对四个态的布居数随时间的演化进行了数值模拟。模拟结果表明,泵浦光场的拉比频率强度和失谐量对布居转移率的影响和探测光场、耦合光场的拉比频率强度及失谐量对布居转移率的影响不同;自发辐射诱导相干(SGC)对布居转移率的影响不大。但当它们选取适当参数的时候,基态的布居几乎可以全部被转移到目标态能级。

Fenna-Matthews-Olson捕光复合物中的冗余结构（英文）

研究了绿色硫细菌中捕光天线复合物Fenna-Matthews-Olson的一个子单元和反应中心的能量传递.通过细菌叶绿素分子的能量和耦合强度,构建了包含反应中心的哈密顿量及约化模型.通过级联运动方程研究了不同分子间和反应中心的激子布居演化.计算了Fenna-Matthews-Olson及其约化模型的二维三阶光子回波谱,获得能量传输过程中不同激子态间的相干性.结果表明在能量捕获过程中,Fenna-Matthews-Olson复合物存在冗余结构.

Ramsey-CPT原子频标的高性能小型脉冲微波源研究

根据Ramsey-CPT原子频标对脉冲微波源高性能小型化的要求,采用直接数字频率合成器激励锁相环频率合成器,再结合可编程数字功率衰减器和阻抗匹配电路,从而实现具有高稳定度、高分辨率、快跳频速度、低相位噪声、小体积、小步长扫描的脉冲微波源。比较应用于Ramsey-CPT原子频标的脉冲微波源方案,介绍脉冲微波源的基本原理,简述其具体实现方法,并通过仿真优化得到最佳的输出性能。实现的脉冲微波源具有优良的技术性能,进一步提高了Ramsey-CPT原子频标输出频率的性能。同时,达到了设计小型化的要求,有利于Ramsey-CPT原子频标的便携式应用。

啁啾Gauss飞秒脉冲驱动三能级系统的超快布居转移

利用不含旋波近似(RWA)的Schrdinger方程的数值解,研究了线性极化的啁啾Gauss飞秒激光脉冲驱动Ξ型三能级原子系统的超快粒子布居转移。研究结果表明,粒子布居转移主要决定于驱动激光场的Rabi频率(强度)和啁啾率,两跃迁偶极距的比值和脉宽对粒子布居转移也有明显的影响。通过适当选择以上参量的取值,可以实现粒子布居99.6%的转移。

相干光学声子的操控以及对能量输运过程的影响

利用脉冲整形器生成双脉冲泵浦光,通过调整双脉冲的间隔时间,在不改变泵浦光能量密度的前提下,实现了相干光学声子的增强和完全消除,进而研究了相干光学声子对半导体能量输运过程的影响。实验直接验证了光学声子在超快能量输运过程的重要作用。相干光学声子增强时测量得到的热电子冷却以及晶格加热的特征时间均减小,因此激发相干光学声子可提高超快能量输运效率。当电子与晶格处于热平衡状态时,相干光学声子增强和消除前后反射信号的下降趋势相同,因此光学声子对热量输运没有显著影响。