中间态引入量子干涉的三光子共振非简并六波混频

理论研究了五能级系统中三光子共振非简并六波混频(NSWM) 由于中间能级加入耦合光场而产生的量子干涉效应. 分析了耦合光场对三光子共振NSWM信号以及频谱的影响. 研究发现, 在强耦合场作用下, NSWM的频谱出现了Autler-Townes分裂, 它反映的是两个缀饰态的能级, 量子干涉可以使NSWM信号被抑制或增强. 提出利用量子干涉对NSWM信号产生增强作用, 可以由耦合场产生的缀饰态代替原子固有能级, 成为三光子共振的中间态, 从而控制耦合场来选择三光子共振的中间态的位置.     

缀饰态理论在碰撞能量转移过程中的应用

利用缀饰态理论研究了由分子和原子组成的混合共振系统中分子和原子之间的碰撞能量转移过程.结果发现:在单模强激光场作用下,该混合共振系统由于发生了碰撞能量转移,而使得粒子在相应能级上产生重新布居,并在一定条件下呈现出量子干涉增强效应,导致了不同缀饰态能级之间出现交叠区.这一结果与现有实验报导相符,为研究多能级系统的量子干涉效应提供了一种新的理论途径.     

N5B五能级系统中重复缀饰四波混频研究

从理论上研究了N5B五能级系统中一个激光场重复缀饰四波混频过程.结合能级图分析,从它特殊的Autler-Town分裂峰中可以非常清晰地看出其重复缀饰的作用.还研究了在强Probe场和强耦合场下N5B五能级下缀饰四波混频信号的抑制增强现象.采取独特的处理方法——独立作用法,研究结果表明一个激光场作用于N5B五能级系统时存在两次缀饰,并形成缀饰能级的二重分裂或者三重分裂,不同于多个耦合场对原子的多重缀饰作用.应用于非线性光谱术中对多峰结构的研究. 关键词： 四波混频 电磁感应透明 重复缀饰     

引入量子干涉的双光子共振非简并四波混频

研究了级联四能级系统中双光子共振非简并四波混频(NFWM)由于加入耦合光场而产生的量子干涉效应，发现在强耦合场作用下NFWM频谱呈现AT劈裂，它反映的是两个缀饰态的能级.量子干涉还使NFWM信号被抑制或增强.此方法牵涉到三光子共振，因此可以成为研究原子或分子高激发态的有效光谱学工具. 关键词： 四波混频 量子干涉     

五能级原子开放系统中的多波混频共存特性

研究了受强缀饰场作用的五能级原子系统所产生的多波混频共存特性.研究发现,通过调节激光束方向,沿同一方向出射的八波混频、双缀饰四波混频和单缀饰六波混频信号因共用能级的原子相干产生而出现竞争现象,通过控制缀饰场减弱四波混频和六波混频信号强度,可以达到增强八波混频信号的目的.还对级联和并联两种不同缀饰方式下双缀饰四波混频过程的差别进行了详细分析. 关键词： 双缀饰四波混频 单缀饰六波混频 八波混频 抑制增强     

基于简并四波混频的双信道双频段增益谱

基于大规模光通信中频分复用的需求,本文以热原子的简并四波混频为模型,研究了具有双频段特性的双信道增益光谱.一束缀饰场诱导激发态能级发生分裂,由于量子干涉效应,四波混频信号的增益在双光子共振处被抑制,从而使增益谱线的包络由单频段转变为"M"型的双频段结构.同时,缀饰场还提高了相干基态的原子布居,进一步增强了四波混频信号的强度.最终实验上在铯原子气室内获得了一对具备双频段的双信道高增益光谱,并通过调节缀饰场的强度和频率失谐,实现了对双增益峰频率间隔的有效操控.     

利用暗态共振之间的相互作用提高Kerr非线性

分析了利用双暗态共振之间的相互作用提高Kerr 非线性的方案,采用微扰理论和密度矩阵方法导出三阶极化率实部随外加相干驱动场失谐量变化的关系.结果表明,随着相干驱动场失谐量的增加,双暗态共振之间干涉使得Kerr非线性的最大值也随之变大且逐渐进入电磁感应透明窗口,并使用缀饰态理论对其产生的机制给予相应的解释.证明了在具有双暗态共振的四能级原子系统中获得无吸收巨Kerr非线性实现的可行性.     

多窗口可调谐电磁诱导透明研究

当两束激光以Λ-构型作用于三能级原子系统并满足双光子共振条件时，探测激光场吸收谱呈现电磁诱导透明(EIT)特征.若再加一个微波控制场作用于该三能级系统的两个低能级跃迁之间，会导致探测吸收特性明显变化，EIT窗口将发生劈裂.通过求解相应的密度矩阵方程，揭示了外加微波场作用下EIT窗口的变化规律，并给出了相应的缀饰态解释.研究结果表明，在适当的条件下, 电磁诱导透明呈现三重结构，而EIT窗口的频率位置取决于微波控制场的拉比频率及频率失谐量.因此通过改变微波控制场的参数可以实现多EIT窗口的频率调谐. 关键词： 电磁诱导透明 量子相干 频率调谐 多窗口EIT     

缀饰原子系统中双光子共振非简并四波混频

本文研究了缀饰原子系统中的双光子共振非简并四波混频.理论上我们研究了多普勒增宽的四能级系统中耦合光场对双光子共振非简并四波混频的影响,发现加入强耦合场后,非简并四波混频频谱出现Autler-Townes分裂;在不同双光子共振失谐时,由于量子干涉双光子共振非简并四波混频的信号能够被抑制或增强.实验上我们在Ba原子蒸汽中,通过引入基态6s2和自电离里德堡态6pnd之间的原子相干证实了该现象.本方法提供了一种不仅可以测得共振频率和横向弛豫,而且可以测得两个高激发原子态之间的跃迁的偶极矩阵元的新的光谱学工具.     

非厄米哈密顿量的物理意义

分析了一个脉冲激光与原子相互作用的四能级系统，并考虑最上层能级的自电离过程，从而引入非厄米哈密顿量.在缀饰原子模型下，通过直接求解此哈密顿量的本征值与本征函数，得到系统布居的演化函数.与数值方法所得演化函数的对比表明二者相当符合，从而肯定了非厄米哈密顿量在量子力学框架中的地位，并得到其本征值虚部的物理意义.这将使传统量子力学中力学量的定义得以拓展. 关键词： 非厄米哈密顿量 缀饰原子模型     

Coherent population transfer in four-level ladder systems by single frequency-chirped laser pulse

Adiabatic passage induced by a frequency-chirped laser pulse in four-level ladder systems is investigated. Two different strategies for efficient population transfer (intuitive and counterintuitive laser pulse) are analyzed. For the larger detuning, the four-level ladder system can be reduced to a two-level system with which we are familiar. For the smaller detuning, the main conditions for realization of population transfer are the following: the width of the transform-limited laser pulse envelope frequency spectrum (without chirp) must be smaller and the peak Rabi frequency of the pulse must be larger than the detuning ε₂₁ and ε₂₁∼ε₃₂ in the case of the three-photon resonance. With this laser pulse, it is possible to achieve complete population via the intermediate levels by three successive adiabatic passages. Complete inversion is also obtained by a counterintuitive direction of the frequency sweep.     

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.     

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.     

Stimulated Raman adiabatic passage in fields with stochastic amplitudes

A theoretical analysis is presented of the effect of correlation between fluctuations of laser pulse amplitudes on population transfer between the states of a three-level atom coupled by the laser field. The carrier frequencies of the pulses are tuned to resonance with the transitions between the ground and excited states, |〈 and | 2〈, and the excited and metastable states, |2〈 and |3〈, in a lambda-type configuration. The laser pulses are timed so that population transfer between states |1〈 and | 3〈 is made possible by stimulated Raman adiabatic passage (STIRAP) in the absence of fluctuations. STIRAP does not occur when the laser fields are not correlated. When the fluctuations of one pulse amplitude duplicate those of the other, STIRAP can be observed for pulse amplitudes larger than those required in the absence of fluctuations.     

Adiabatic population transfer in multistate chains via dressed intermediate states

The well-known process of stimulated Raman adiabatic passage (STIRAP) provides a robust technique for achieving complete population transfer between the first and last state of a three-state chain, with little population, even transiently, in the intermediate state. The extension of STIRAP to general N-state chainwise-linked systems continues to generate interest. Recently Malinovsky and Tannor (Phys. Rev. A 56, 4929 (1997)) have shown with numerical simulation that a resonant pulse sequence, which they term “straddle STIRAP”, can produce (under appropriate conditions, including specific pulse areas) complete population transfer with very little population in intermediate states. Their proposal supplements a pair of counterintuitively ordered delayed laser pulses, driving the first and last transition of the chain and corresponding to the pump and Stokes pulses in STIRAP, with one or more additional strong pulses of longer duration which couple the intermediate transition(s) and overlap both the pump and the Stokes pulses. In this paper, we modify the “straddling” Malinovsky-Tannor pulse sequence so that the intermediate couplings are constant (and strong), at least during the times when the pump and Stokes pulses are present, and the intermediate states therefore act as a strongly coupled subsystem with constant eigenvalues. Under this condition, we show that the original N-state chain is mathematically equivalent to a system comprising N-2 parallel -transitions, in which the initial state is coupled simultaneously to N-2 dressed intermediate states, which in turn are coupled to the final state. The population transfer is optimized by suitably tuning the pump and Stokes frequencies to resonance with one of these dressed intermediate states, which effectively acts as the single intermediate state in a three-state STIRAP-like process. We show that tuning to a dressed intermediate state turns the system (for both odd N and even N) into a three-state system - with all of the properties of conventional STIRAP (complete population transfer, little transient population in the intermediate states, insensitivity to variations in the laser parameters, such as pulse area). The success of the tuning-to-dressed-state idea is explained by using simple analytic approaches and illustrated with numerical simulations for four-, five-, six- and seven-state systems. Received: 17 April 1998 / Accepted: 15 June 1998     

Dressed states analysis of lasing without population inversion in a three-level ladder scheme: Approximate analytic time dependent solutions

A dressed-state study of lasing without population inversion from a three level atom interacting with a bi-chromatic laser field, in the ladder configuration, is formulated. We allow the atomic system to be dressed by both laser filed photons (double dressing). The evolution of the system under consideration is being explored both analytically and numerically, within the transient regime. Time dependent approximate analytic solutions for dressed-state populations and coherences are derived, within the so called “secular approximation,” under resonant conditions. We also present time dependent numerical solutions for population and coherences in the off-resonance regime. A spectral analysis is also performed revealing the structure of various dressed states transitions. These are shown to be composed of quintets centered about the frequencies of the coupling and probe laser fields and having sidebands located symmetrically at positions shifted from line center at the Rabi and double Rabi frequencies.     

Coherence generation and population transfer in a three-level ladder system

This work explores the effect of spontaneous emission on coherence generation and population transfer in a threelevel ladder atomic system driven by two pulses in counterintuitive order.With adiabatic evolution and the weakdephasing approximation,we find that a large coherence and population transfer can be achieved even with spontaneous decay rate.The maximum coherence and population transfer decrease with the increase of spontaneous decay rate from the highest state to intermediate state.But this effect can be compensated by shortening the pulse width and enlarging the delay time.Results show that the coherence generation and population transfer never depend on the spontaneous decay rate from the intermediate state to ground state.The validity of the analytic solution is examined by numerical calculation.     

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.     

Resonant scattering of photon by electron in the presence of the pulsed laser field

The scattering of photon by electron in the presence of the field of the low-intensity circularly-polarized pulsed laser wave is analyzed at a laser pulse duration that is significantly greater than the characteristic oscillation time. The conditions for the resonance process in which the intermediate particle is located in the vicinity of the mass surface are determined. The existence of three resonance ranges is demonstrated. The first one corresponds to the resonance of direct diagram, and two ranges correspond to the resonance of exchange diagram via electron and positron intermediate states. The conditions under which only the resonance of the direct diagram takes place are determined, and the probability of such process is calculated. It is demonstrated that the resonance probability can be significantly greater than the probability of the Compton effect in the absence of the external field.     

HF和DF分子双光子布居转移过程中的同位素效应

通过求解含时薛定谔方程,研究了XF(X=H,D)分子体系双光子共振条件下布居转移过程中的同位素效应.对于这两个分子体系,基电子态上的振动能级v=0和v=2被考虑成初始态和目标态.详细讨论了激光场峰值强度和脉冲持续时间对布居转移过程的影响.脉冲持续时间需要长于860 fs才能保证DF分子体系可以获得较为显著的布居转移几率(大于80%),而对于HF分子体系,该参数只需长于460 fs.与HF分子体系相比,中间态v=1和较高的v=3振动态会对DF分子体系的双光子共振布居转移过程产生更重要的影响.