Spontaneous emission from a Λ three-level atom in an anisotropic photonic crystal

The spontaneous emission properties of a Λ type atom embedded in a three-dimensional anisotropic photonic crystal are investigated. Only one of the two atomic transition frequencies is considered near the photonic band edge. The atomic decay properties such as the time-evolution of the excited-state population and the instant and effective decay rates are studied in detail. It is found that there exists a wide region for the difference of the transition frequency from the band edge, in which only diffusion fields with frequencies being near or far away from the band edge appear in the emitted field. The spontaneous emitted field and its spectrum depend not only on the detuning of the transition frequency from the band edge, but also on the distance from the atom. Therefore, during the propagating process, the propagating field is partially transferred into the diffusion field.     

Resonance fluorescence spectrum of a three-level atom driven by coherent and stochastic fields

The dressed-state populations and the resonance fluorescence spectrum of a V-type three-level atom driven by a strong coherent field and a weak stochastic one simultaneously are investigated. There can be significant population inversion due to the effect of the stochastic field. The atomic resonance fluorescence spectrum can be controlled by adjusting the frequency difference between the coherent field and the stochastic one and the coherent Rabi frequency. Peak suppression and line narrowing occur under appropriate conditions. Received 23 June 2000 and Received in final form 18 January 2001     

Intensity correlations in a coherently prepared Rb vapor in a magnetic field

We have studied the intensity correlations between two orthogonally linearly polarized components of a laser field propagating through a resonant atomic medium. These experiments have been performed in a rubidium atomic vapor. We observe that the correlations between the orthogonally polarized components of the laser beam are maximal in the absence of a magnetic field. The magnitude of the correlations depends on the applied magnetic field, and the magnitude first decreases and then increases with increasing magnetic field. Minimal correlations and maximal rotation angles are observed at the same magnetic fields. The width of the correlation function is directly proportional to the excited state lifetime and inversely proportional to the Rabi frequency of laser field.     

场频率变化时多光子J-C模型中原子的动力学特性

利用多光子J-C模型,在旋波近似下,研究了场频率随时间变化时二能级原子通过多光子跃迁与单模辐射场相互作用系统中原子的动力学特性,分析了光场频率随时间以正弦函数形式作小量变化的典型情况,利用数值计算方法给出原子算符S3(t)平均值随时间的演化曲线.研究结果表明:原子算符S3(t)平均值随时间的演化受场频率随时间正弦函数形式变化的调制,场频率振荡的幅值u越大调制作用越强.     

Controllable Optical Bistability and Multistability in a Four-Level Atomic System with Closed-Loop Configuration

We theoretically investigate optical bistability （OB） and multistability （OM） behaviour of a closed-loop configuration atomic system driven by a degenerate coupling- field and a degenerate probe field inside a unidirectional ring cavity. It is found that the OB and OM behaviour can be controlled by adjusting- the intensity and the frequency detuning of the coupling- field, respectively. Interestingly, our numerical results show that it is easy to realize the transition from OB to OM or vice versa by adjusting- the intensity of the coupling- field under a appropriate frequency detuning. The effect of the atomic cooperation parameter on the OB behaviour is also discussed.     

变频率光场与二能级原子的相互作用：双光子过程

研究了二能级原子与单模电磁场相互作用时的双光子过程,主要考虑了在相干态初始条件下场频率发生变化时的情况,讨论了场频率随时间作正弦缓慢变化对原子布居数反转、光场压缩与原子压缩等特性的影响.结果显示,场频率的改变将使得原子布居数反转的崩塌回复周期增大,回复值减小,而光场及原子压缩效应减弱. 关键词： 布居数反转 光场压缩 原子压缩 双光子过程     

非旋波近似下频率变化的场与原子的相互作用

研究了非旋波近似下频率随时间变化的相干态光场与二能级原子的相互作用，主要讨论了光场频率随时间作正弦和方波变化两种典型情况下，原子布居数反转随时间的演化特性. 当光场频率随时间作正弦变化时，原子布居数反转的崩塌-回复过程和由虚光子过程引起的快速振荡均会受到影响. 当光场频率随时间以方波形式变化时，脉冲调制不仅在原子布居数反转随时间演化过程中诱导出新的崩塌-回复过程，而且可以引起虚光子快速振荡的突变. 关键词： Jaynes-Cummings模型 非旋波近似 原子布居数反转     

Effects of an applied low frequency field on the dynamics of a two-level atom interacting with a single-modefield

The effects of an applied low frequency field on the dynamics of a two-level atom interacting with a single-mode field are investigated. It is shown that the time evolution of the atomic population is mainly controlled by the coupling constants and the frequency of the low frequency field, which leads to a low frequency modulation function for the time evolution of the upper state population. The amplitude of the modulation function becomes larger as the coupling constants increase. The frequency of the modulation function is proportional to the frequency of the low frequency field, and decreases with increasing coupling constant.     

频率变化的压缩态光场与原子的相互作用

研究了频率随时间变化的压缩态光场与二能级原子的相互作用，主要讨论了光场频率随时间作正弦调制和脉冲调制两种典型情况下原子布居数反转随时间的演化特性.当光场频率随时间作正弦调制时，不仅光场频率调制，而且压缩态的压缩系数和压缩相位均对原子布居数反转的崩塌-回复过程有影响.当光场频率随时间作脉冲调制时，脉冲调制的突变使各拉比振荡之间的相干性发生改变，并在原子布居数反转随时间演化过程中诱导出新的崩塌-回复过程，尤其在脉冲出现的区间内，原子布居数反转表现出持续的小幅快速振荡，这与压缩态的压缩系数无关. 关键词： Jaynes-Cummings模型 压缩态 原子布居数反转     

Controlling nonclassical properties of the two-photon process by a time-varying field

The interactions between a two-level atom and a field via two-photon transition without rotating wave approximation have been investigated. We emphasize the dynamic behaviors of the atomic population inversion, the field squeezing, and the atomic dipole squeezing numerically when the field frequency varies with time in the forms of sine and rectangle. Some interesting phenomena are discovered and discussed. The good periodic character of the atomic population inversion in the standard two-photon Jaynes--Cummings model is weakened by the influence of the sine field frequency modulation. The rectangular field frequency modulation can change the correlation among different oscillations suddenly and induce new collapse-revival processes of the atomic population inversion. The field squeezing increases at the beginning of time, but then decreases and loses as the time increases after it reaches the maximum due to the sine modulation. The effects of the rectangular modulation on the field squeezing depend mostly on the appearance time of the modulation. The atomic dipole squeezing is weakened under the influence of the sine or rectangular modulation. Our results indicate that it is possible to perform the dynamic controlling of the system properties by changing the parameters of the system with time. This implies that one can dynamically control a quantum information process by choosing the system modulation properly.     

Control of the optical multistability in a three-level ladder-type quantum well system

We theoretically investigated a hybrid absorptive-dispersive optical multistability (OM) behavior in a three-level ladder-type quantum well system inside a unidirectional ring cavity. We find that the frequency detuning of the control field and the electronic cooperation parameter as well as the total decay rates can affect the optical multistability behavior dramatically, which can be used to manipulate efficiently the threshold intensity and the hysteresis loop. The effect of the intensity of the control field on the OM is also studied. Our study is much more practical than its atomic counterpart due to its flexible design and the wide adjustable parameters. Thus it may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.     

Observation of collimation and decollimation of an atomic beam in a misaligned standing wave

This paper reports an experimental study on the collimation and decollimation of an atomic beam in a misaligned standing wave, in which the effective detuning caused by the Doppler effect is affected by the longitudinal velocity of the atomic beam. The experiment shows that in a strong field with red detuning between laser field and atomic transition frequency, laser heating in a normal standing wave becomes laser cooling in a misaligned standing wave for an approriate misalignment angle. For blue detuning, laser cooling in a standing wave can also become laser heating in a misaligned standing wave for an appropriate condition. These results ca be used in controling atomic motion.     

Atomic clocks based on coherent population trapping: a review

The paper gives an overview of the use of the coherent population trapping phenomenon (CPT) in alkali-metal atoms in the implementation of atomic frequency standards. Several avenues are examined. These include: the approach using a combination of the CPT phenomenon and the Ramsey separated interaction field technique on an atomic beam; the passive approach in a cell in which the microwave hyperfine resonance excited by the CPT phenomenon is detected directly on the transmitted radiation; the maser approach in which the same resonance is observed by means of stimulated emission in a microwave cavity-cell arrangement; and, finally, the proposed approach using pulses in a time sequence that implements the combined CPT–Ramsey separated interaction field technique in time rather than in space. A review of field and laboratory implementations using these approaches is made.     

High-resolution atomic channeling using. velocity-selected atomic beam

High-resolution atomic channeling using velocity-controlled atoms may be able to overcome precision limitations of the conventional atom lithography. We have experimentally clarified the dependence of line width and contrast of atomic patterns in the channeling region on the velocity spread of the atomic source for the first time. Thermal or velocity-selected atomic beams prepared with a one-dimensional magneto-optical trap were employed as the atomic sources. We investigated the channeling characteristics by measuring the frequency shifts of the atomic absorption spectra in an intense standing wave light field. As a result, we can show that narrower line width and higher contrast atomic patterns are obtained as the velocity spread becomes narrower. An atomic pattern with an estimated line width of 57 nm was generated when the velocity spread of the atomic source was almost 50 m/s, that is, 1/6 that of the thermal beam. Received: 16 June 2001 / Published online: 7 November 2001     

Field and dipole squeezing in a driven degenerate Λ quantum-beat system

The properties of field squeezing and atomic dipole squeezing in a coherent-microwave field driven degenerate Λ quantum-beat system were theoretically investigated. Numerical calculations indicate that the driving microwave may enhance or suppress both dipole squeezing and cavity-field squeezing, depending on the atomic energy level splitting and the microwave Rabi frequency.     

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.     

双色激光场对运动原子的辐射压力

本文研究了双色行波场对运动原子的辐射压力，通过数值计算，分别得到了在不同光强，不同频率，不同传播方向条件下，原子在双色场中的受激跃迁速率和辐射压力随速度变化的关系。结果表明：双色场对原子的辐射压力和行波场及驻波场相比，有着许多不同特点，这些特点可以在激光冷却中性原子，原子速度选择，原子动量扩散的研究中加以利用。     

Three-Photon Resonant Nondegenerate Six-Wave Mixing in a Dressed Atomic System

We report a three-photon resonant nondegenerate six-wave mixing （NSWM） in a dressed cascade five-level system. It has advantages that phase match condition is not stringent and NSWM signal is enhanced tremendously due to the multiple resonance with the atomic transition frequencies. In the presence of a strong coupling field, the threephoton resonant NSWM spectrum exhibits＂ Autler-Townes splitting. This technique provides a spectroscopic tool for measuring not only the resonant frequency and dephasing rate but also the transition dipole moment between two highly excited atomic states.     

场频率随时间变化对原子偶极压缩效应的影响

利用J-C模型,考虑场频率随时间以正弦函数形式作小量变化,在旋波近似下,研究了二能级原子通过单光子跃迁与单模辐射场相互作用系统中原子算符Sy压缩效应的演化规律.利用数值计算方法给出压缩量随时间的演化曲线.研究结果表明:原子算符压缩效应的演化受场频率随时间正弦函数形式变化的调制,场频率振荡的幅值u越大调制作用越强.随场频率变化的幅值u的增大,压缩效应减弱.在场频率振荡的幅值u大于一定值后,压缩量将按场频率周期性的变化规律作周期性振荡,