Increasing of population trapping and transferring in a modified laser-induced continuum structure system by phase control

The atomic coherent population trapping in the system of an atom with one ground state, a pair of excited states and a set of continuum states, interacting with two temporally separated sets of laser pulses with different phases is investigated. The relative phases of laser pulses on the amount of atomic populations trapped in the three bound states and the efficiency of population transfer are analyzed.     

COHERENT POPULATION TRAPPING IN MULTILEVEL LASER-INDUCED CONTINUUM STRUCTURE SYSTEM INCLUDING CASCADE TWO-PHOTON PROCESSES

We have investigated the atomic coherent population trapping in a mul tilevel laser-induced continuum structure system including cascade two-photon processes, in which two sets of quasicontinua of excited levels to be modeled as the Bixon-Jortner quasicontinuum are laser-embedded into a previously structu reless atomic continuum.The condition leading to the atomic coherent population trapping and the coherent population trapping state are given explicitly. And th e effects of the Fano factors, the laser intensities and the detunings on the am ount of population trapped in the atomic bound states and the populations distri buted in the two sets of quasicontinua are also examined.     

On the possibility of polarizing atoms and nuclei by pulsed electromagnetic fields without using ultra-low temperatures

A method is proposed for fast and deep polarization of the system of hyperfine sublevels of the ground state of an atom having an optical excited state by means of two-component microwave pulses. The pulse of the bichromatic optical field that induces the transitions between the ground state and excited state of the atom is supposed to provide coherence among the hyperfine sublevels of the atomic ground state via the effect of coherent population trapping. The subsequent resonance microwave pulses create the polarization of equally populated ground state sublevels of the atom. The proposed polarization technique may be used for designing the new schemes of quantum computers, for the pulse transformation in optical experiments when light passes through a resonant medium containing rear-earth ions, as well as for producing polarized nuclear targets.     

Dispersion of populations of a multilevel system in a strong field of laser emission and a magnetic field

Using the theory and the calculation method developed previously, numerical experiments on the study of dispersion of populations of a multilevel atomic system in strong fields of laser radiation in resonance with adjacent transitions and in a constant magnetic field are conducted. The effect of the magnetic field strength on the character of coherent population trapping in a multilevel system is studied. It is shown that the effect, depending on the magnetic field strength, may be observed for both and for one of the magnetic sublevels of the level that is doubly degenerate in the magnetic quantum number, for which resonance fluorescence is studied. The possibility of obtaining population inversion for magnetic sublevels in the excited state of a multilevel atom under an appropriate choice of parameters is demonstrated.     

原子相干对里德伯原子稳定性的影响

研究了含级联双光子过程的多束缚态激光场诱导原子连续态结构系统中原子的相干捕获,给出了产生相干捕获的条件及暗态的表达式,讨论了原子初态和激光强度对原子相干捕获及粒子布居值在束缚态上分布的影响,揭示了原子相干对稳定里德伯原子的重要作用。     

双通道离化系统的相干控制

研究了中间态为准连续态的双通道离化系统中激光的相对相位对稳态光电子谱的影响,给出了系统发生相干俘获的条件及相应的系统状态,讨论了俘获率对激光强度、频差及准连续态能级间隔的依赖关系 关键词： 准连续态 相干控制     

Mathematical modeling of the population dynamics of “dark” states of a three-level system

Mathematical modeling of the population dynamics is performed for states of a three-level system (atom) with a V-type configuration transforming a light pulse. It is assumed that the excited eigenstates of the atom are degenerate and coupled by coherent interaction, one of the states being radiating (radiative), while the other state is nonradiating (??dark??). The population dynamics of atomic states is described on the basis of numerical solutions of equations for the matrix elements of the density operator. The dependence of the efficiency of population of the atomic dark state from the values of the parameters of an irradiation pulse and from the ratio of the period of population oscillations of excited atomic states (caused by their coherent interaction) to the lifetime of the atomic radiating state is determined. Typical examples of the time dependence of the population of states of the atom considered are presented for the cases of irradiation by a short (as compared to the lifetime of the radiating state) sinusoidal light pulse and by a long rectangular light pulse with the resonance carrier frequency.     

三能级原子与少周期脉冲串作用中的相干布居捕获

研究了少周期脉冲串作用下三能级原子中的布居转移和相干布居捕获现象.在非旋波近似的情况下求解了密度矩阵方程.研究结果表明在等时间间隔的锁相脉冲作用下,系统能级的布居逐步转移并积累,系统基态相干也逐步积累.在满足脉冲重复频率为基态能级频差的整数分之一倍时,三能级系统和频率梳中两梳齿频率成分作用形成相干布居捕获现象,原子暗态布居值达到最大,介质对脉冲透明.在适当选取少周期脉冲参量的情况下,在0.5个ns的时间内三能级系统相干性演化到最大后到达稳态,相干布居捕获发生.与脉宽为100个fs的多周期脉冲相比,少周期脉冲串在介质中建立相干布居捕获的时间缩短两个数量级.由于频率梳中与三能级系统发生作用的梳频成份有相同的频移,相干布居捕获的条件双光子共振仍然满足.因而,当两基态能级频率差较大时,如果选取少周期脉冲载波频率为系统能级1至2和1至3的传输频率之和的一半ω=(ω₁+ω₂)/2,室温下原子热运动的引起的多普勒频移并不会破坏相干布居捕获.     

Coherent Population Trapping in a Λ-Configuration Photoionization System in the Presence of an Autoionizing State

We investigate the atomic coherent population trapping in the system of two-mode quantized field interacting with a A-configuration atom with two lower bound states, one autoionizing state and a flat atomic continuum. The states of the field which traps the atom in its two lower bound states are given and the influence of the field induced continuum structure is examined.     

Spontaneous-emission suppression on arbitrary atomic transitions

We propose a very simple scheme to slow down the usual exponential decay of upper state population in an atomic two-level system considerably. The scheme uses an additional possibly intense field with frequency lower than the total decay width of the atomic transition. This allows for additional decay channels with the exchange of one or more low-frequency photons during an atomic transition. These channels may then interfere with each other. The intensity and frequency of the low-frequency field are shown to act as two control parameters modifying duration and amount of the population trapping. An extension of the scheme to include transitions to more than one lower state is straightforward.     

V型原子系统中相干布居俘获的相干相位调制研究

在延迟脉冲激光场作用下的V型原子系统中，实现了对相干布居俘获，电磁感应透明的相干相位调制，选择适当的能级其调制频率可以达到飞秒量级.利用数值和解析分析得到了延迟脉冲和叠加态粒子数布居的关系，以及粒子布居受光场相位调制的特点和变化规律.利用这种机理可以实现飞秒量级的量子开关作用. 关键词： 相干相位调制 相干布居俘获 电磁感应透明 量子开关     

Interactions of condensate atoms in the process of velocity-selective coherent population trapping

The properties of a one-dimensional atomic Bose condensate are studied under the assumption that the condensation leads to a state of velocity-selective coherent population trapping. This state is characterized by the quantum correlation (entanglement) between the intrinsic angular momentum of an atom and its translational motion underlying nontrivial features of the condensate. The effects of weak interatomic interaction are taken into account. The steady state of above-condensate atoms corresponding to the slow decay of the state with coherent population trapping is found. The dynamic problem concerning the evolution of the system of above-condensate atoms after switching off the optical field forming the state with coherent population trapping is solved. The solution is found by the diagonalization of the Hamiltonian based on introducing the Bogoliubov quasiparticles with the unusual dispersion law.     

Unexpected Population Inversion in a Λ-type Medium

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Population dynamics of excited atoms in non-Markovian environments at zero and finite temperature

The population dynamics of a two-atom system, which is in two independent Lorentzian reservoirs or in two independent Ohmic reservoirs respectively, where the reservoirs are at zero temperature or finite temperature, is studied by using the time-convolutionless master-equation method. The influences of the characteristics and temperature of a non-Markovian environment on the population of the excited atoms are analyzed. We find that the population trapping of the excited atoms is related to the characteristics and the temperature of the non-Markovian environment. The results show that, at zero temperature, the two atoms can be effectively trapped in the excited state both in the Lorentzian reservoirs and in the Ohmic reservoirs. At finite temperature, the population of the excited atoms will quickly decay to a nonzero value.     

Probe gain with population inversion in a four-level atomic system with vacuum-induced coherence

For a four-level atomic system with a doublet of closely spaced levels, we find that, owing to the coherence that results from the vacuum of the radiation field, population trapping at excited levels and probe gain with population inversion can be achieved with weak incoherent pumping. This gain is different from both the conventional lasing gain and gain without inversion in that there exists population inversion on probe transitions but the inversion is achieved by the vacuum-induced coherence.     

Six-Fold Degenerate Dark States in a Four-Level Atomic System

With all driving fields on Raman resonance, a tripod-type atomic system quickly evolves into a dark state decoupled from the lossy excited level. The dark state depends strongly on field Rabi frequencies, spontaneous decay rates, and the initial atomic population in a complicated way. Analytical results reveal that it is a sixfold degenerate dark state with its three components superposed both coherently and incoherently due to population redistribution from spontaneous emission.     

Quantum interferences in coherent population trapping of a cold double Λ-type atom

We investigate quantum interferences in coherent population trapping of a cold double Λ-type four-level atomic system driven by two counterpropagating laser fields. We study both decoherence and enhanced-coherence actions resulting from the multi-transition pathways in building up the trapping state, and analyze the system operating with and without external coherences in various configurations of the atomic dipole moments.     

AC Stark-shift in CPT-based Cs miniature atomic clocks

We report on studies on the light-shift in caesium miniature atomic clocks based on coherent population trapping (CPT) using a micro-fabricated buffer-gas cell (MEMS cell). The CPT signal is observed on the Cs D1-line by coupling the two hyperfine ground-state Zeeman sublevels involved in the clock transition to a common excited state, using two coherent electromagnetic fields. These light fields are created with a distributed feedback laser and an electro-optical modulator. We study the light-shift phenomena at different cell temperatures and laser wavelengths around 894.6?nm. By adjusting the cell temperature, conditions are identified where a miniature CPT atomic clock can be operated with simultaneously low temperature coefficient and suppressed light-shift. The impact of the light-shift on the clock frequency stability is evaluated. These results are relevant for improving the long-term frequency stability of CPT-based Cs vapour-cell clocks.     

Optimization of stabilization regimes in atomic clocks,based on the effect of coherent population trapping

Using the atomic density matrix formalism, we investigate the dynamic regime of formation of the error signal for resonances of coherent population trapping excited in a three-level Λ-system by a bichromatic field. The optimal parameters of harmonic modulation used in the frequency locked loop are determined with allowance for low-frequency noise.     

两模微波激射器中三能级原子布居数随时间的演化

在相互作用绘景中,得到了两模微波激射器的腔模与注入其内的Λ型三能级原子构成的相互作用系统的演化算符的矩阵表示,以及该系统的态函数随时间的演化关系,在此基础上导出了原子布居数随时间的演化关系,由此可进一步研究布居数的振荡、反转和捕获等问题.