Effect of surface reconstruction on the photoemission cross-section of the Au(111) surface state

The photoemission cross-section of the Shockley surface state of Au(111) is studied over a wide range of photon energies both experimentally and theoretically. The measurements are fully understood based on the theoretical analysis within a one-step ab?initio theory of photoemission. The constant initial state spectrum is shown to be very sensitive to the structure of the topmost atomic layer. A maximum in the constant initial spectrum at 60?eV is identified as a fingerprint of the Au(111) surface reconstruction.     

Effect of the final-state interaction on the initial core–hole lifetime: the case of the 4s-hole lifetime of Sn metal

The first theoretical study of the effect of the final-state interaction on the initial core–hole lifetime is presented. The 4s-hole lifetime width of Sn metal is calculated by an ab-initio atomic many-body theory (Green’s function method). When the final-state interaction in the 4p4d two-hole state, created by the 4s⁻¹−4p⁻¹4d⁻¹ f super Coster–Kronig (CK) transition of the initial 4s hole, is explicitly taken into account, the ab-initio atomic many-body calculation of the 4s-hole X-ray photoelectron spectroscopy (XPS) spectrum of Sn atom can provide excellent agreement with experiment in both the 4s-hole energy and the 4s-hole lifetime width. Otherwise, the many-body calculation underestimates considerably the 4s-hole lifetime width. The 4p4d two-hole state interacts strongly with the 4d triple-hole state by the 4p⁻¹4d⁻¹−4d⁻³ f super CK transition. The interaction affects greatly the initial 4s-hole lifetime width.     

耗散环境下原子-库场相互作用系统中原子的偶极压缩特性

运用全量子理论并结合数值计算方法,研究了处于真空库和热库中原子系统的偶极压缩特性,讨论了原子的初态以及热库的平均光子数对原子偶极压缩特性的影响.研究表明:真空库中,初始处于基态和激发态的叠加态原子,当激发态的粒子布居概率少于基态时,原子的偶极压缩无限接近于零而永远不消失;反之,原子的偶极压缩将在有限的时间内消失;热库中,不管原子初始处于什么态,其偶极压缩都在有限的时间内消失,并且随着热库的平均光子数的增大而消失得越快。     

光场诱导的原子激光的量子相干性

基于伞量子理论,分别研究了几种重要的光场作用下,从原子玻色-爱因斯坦凝聚(BEC)体耦合输出的原子激光的量子相干特性.结果表明,粒子数态光场诱导的原子激光总是反聚束的,相干态光场诱导的原子激光是任意阶相干的,而压缩相干态光场诱导的原子激光总是聚束的.表明用光场诱导产生的原子激光具有与初始光场完全相间的量子相干性质.     

与二项式光场相互作用的运动原子熵压缩

运用量子信息熵理论,研究了二项式光场与运动二能级原子相互作用过程中运动原子的信息熵压缩。讨论了不同的原子初态和场的有关参数对原子信息熵压缩的影响。结果表明：选择原子初态、场模结构、场调节参数及原子运动速度可以调控原子信息熵的压缩方向、偶极矩分量值和压缩周期;适当的选择参数可得到持续性的原子信息熵压缩。     

依赖强度耦合三光子过程下运动原子最佳熵压缩态的制备

为了研究三光子过程中原子与相干态耦合量子体系信息熵压缩随时间演化规律及原子最佳信息熵压缩态的制备,我们采用全量子理论,推导出运动原子与单模简并三光子依赖强度耦合量子体系的精确解;理论上给出制备原子最佳信息熵压缩态的充分及必要条件,并进行了数值模拟验证.研究结果表明:控制相干态场与原子作用时间,切断相干态场与原子的纠缠,选择二能级原子处于等权重相干叠加态,适当选取相干态场与原子的初始位相,可以制备出原子最佳量子信息熵压缩态;调节光腔中场模结构参量,能够得到连续的量子信息熵压缩态.该研究结果在多光子过程低噪声量子信息处理中具有一定意义.     

依赖强度耦合三光子过程下运动原子最佳熵压缩态的制备

为了研究三光子过程中原子与相干态耦合量子体系信息熵压缩随时间演化规律及原子最佳信息熵压缩态的制备,我们采用全量子理论,推导出运动原子与单模简并三光子依赖强度耦合量子体系的精确解;理论上给出制备原子最佳信息熵压缩态的充分及必要条件,并进行了数值模拟验证。研究结果表明：控制相干态场与原子作用时间,切断相干态场与原子的纠缠,选择二能级原子处于等权重相干叠加态,适当选取相干态场与原子的初始位相,可以制备出原子最佳量子信息熵压缩态;调节光腔中场模结构参量,能够得到连续的量子信息熵压缩态。该研究结果在多光子过程低噪声量子信息处理中具有一定意义。     

State-specific,many-electron theory of core levels in metals: The 1s binding energy of Be metal

Cluster ΔSCF theory is combined with calculations of atomic electron correlation to predict the 1s binding energy of Be metal as 115.4 eV, in excellent agreement with experiment (115.2–115.6 eV). Upon creation of the 1s hole, the p character of the valence band increases significantly. This explains the existing discrepancy between the experimental solid state fluorescence yield of Be and the theoretical prediction for the atomic state.     

Effect of the spatial inhomogeneity of a field in a micromaser experiment with the selective measurement of atomic states

It is shown that the theoretical analysis of a micromaser experiment with the selective measurement of atomic states is impossible without consideration of the spatial structure of the field and of the statistical spread of the atomic velocities in the cavity. An approximate theory, ignoring the dynamic effects associated with the mentioned factors, yields not only quantitatively, but also qualitatively different theoretical predictions. The dynamics of the field and the mean number of photons in the trapping states realized in this case differ significantly from the predictions of the idealized standard theory used at present. Along with the process of establishment of the stationary Fock state of the field, under certain conditions, it appears possible to form the quasistationary quantum state of the field with large fluctuations of the number of photons, accompanied by the exit of the field from the cavity (“quasi-dissipation”), and the following stepwise transition into the state of the electromagnetic vacuum. It is shown that, under the conditions of the micromaser experiment, the information about the states of atoms, passed through the cavity, in the case considered, does not allow one to draw an unambiguous conclusion about the state of the field in the cavity.     

Atomic dynamics in the mode－mode competition system

The atomic dynamical properties in the system with competing k-photon and l-photon transitions are studied fully by means of quantum theory. We discuss the influences of the mode－mode competition, the relative competing strengths of the atom and the two-mode field, and the initial state of the system on the atomic dynamics. We show that the presence of the mode－mode competition can result in quite a periodical collapses-revivals of the atomic inversion and the increase of the initial photons of the system can lead to the collapse－revival phenomenon and prolong the revival time of the atomic inversion.     

Coherent control of Kerr nonlinearity via double dark resonances

A theoretical scheme for enhanced Kerr nonlinearity is proposed in a four-level ladder-type atomic system based on double dark resonances (DDRs). We solve the relevant density matrix equations in steady state and utilize the perturbation theory to obtain the analytical expressions for the third order susceptibility of the atomic system. The influence of system parameters on behavior of the first and third order susceptibilities is then discussed. In particular, it is found that an enhanced Kerr nonlinearity with reduced linear and nonlinear absorption is obtained around zero probe detuning under the slow light condition through proper adjusting the laser field intensity and frequency detuning of driving fields. The dressed state analysis is employed to explain the physical origin of the obtained result. The obtained results may be important for all-optical signal processing and quantum information technology.     

Spontaneous emission of atoms in a strong laser field

The spontaneous emission of an atomic system in the field of a high-intensity femtosecond laser pulse is considered within the framework of a consistent quantum-mechanical approach based on an examination of the interaction of a quantum system with a set of quantized field modes in a vacuum state. Both even and odd harmonics of the driving field are shown to appear in the atomic emission spectrum, and the mechanisms of their generation are elucidated. A comparison with the semiclassical theory of laser harmonic generation is made. The semiclassical approach in describing the spontaneous emission in strong laser fields, especially under conditions of significant depletion of the ground (initial) state in a laser field, is shown to be limited.     

边界振动的微腔中的二能级原子

采用全量子理论，对注入腔内的二能级原子、单模腔场和振动边界(视为频率为ω_m的量子谐振子)构成的系统，在相互作用绘景中，求解了该系统的态函数随时间的演化关系，在此基础上得到了原子布居数随时间的演化关系，结果显示布居数在初始值附近振荡，这说明边界的振动是周期性的，它对原子布居数的影响也是周期性的. 关键词： 边界振动的微腔 二能级原子 布居数     

Hydrogen chemisorption on metal surfaces

The adsorption of H atoms on metal (jellium) surfaces has been investigated using linear response theory within the density functional formalism. The adsorbate is represented initially by a 1S orbital on the H atom, which perturbs the jellium surface and indirectly the adsorbate itself. The interaction energy curves, atomic binding energies, induced dipole moments, chemical shifts associated with the adsorbate, and vibrational excitation energies at the equilibrium internuclear separation have been calculated for a single H atom chemisorbed on metal surfaces. The sum of the atomic binding energy and the ionization potential of the H 1S level may be regarded as the initial state energy in the case of photoemission from the chemisorbed H. The rather satisfactory overall agreement between the theory and the experimental results for binding energies, vibrational excitation energies, and dipole moments suggests that this simple formalism could also have useful applications in more complicated chemisorbed systems.     

Structural properties of effective potential model by liquid state theories

This paper investigates the structural properties of a model fluid dictated by an effective inter-particle oscillatory potential by grand canonical ensemble Monte Carlo (GCEMC) simulation and classical liquid state theories.The chosen oscillatory potential incorporates basic interaction terms used in modeling of various complex fluids which is composed of mesoscopic particles dispersed in a solvent bath,the studied structural properties include radial distribution function in bulk and inhomogeneous density distribution profile due to influence of several external fields.The GCEMC results are employed to test the validity of two recently proposed theoretical approaches in the field of atomic fluids.One is an Ornstein-Zernike integral equation theory approach;the other is a third order + second order perturbation density functional theory.Satisfactory agreement between the GCEMC simulation and the pure theories fully indicates the ready adaptability of the atomic fluid theories to effective model potentials in complex fluids,and classifies the proposed theoretical approaches as convenient tools for the investigation of complex fluids under the single component macro-fluid approximation.     

与准Λ型四能级系统互作用光场的熵演化

研究了准Λ型四能级系统与非关联双模相干光场相互作用系统的场熵演化特性,讨论了原子初态、平均光子数及能级劈裂对场熵的影响.该系统包含了二能级原子和三能级原子与单模场相互作用情况.     

铷原子初通道─末通道辐射跃迁矩阵元研究

在相对论性自洽场理论基础上，把量子亏损理论的一个初态到一个末通道的跃迁过程进行了推广：具有相同角动量特征的初态形成所谓的初通道，通过定义重整化矩阵元，统一处理了一个初通道激发到一个末通道的无数个光跃迁过程．作为例子，计算了你原子“s_1/2—p_1/2”，“p_1/2—d_3/2”，“d_3/2—f_5/2”通道之间的光吸收过程．     

Entangling Two Multi-atomic Clusters Through a Cavity Field

Two atomic clusters, which have NA and Ns two-level atoms, respectively, are placed in a cavity but separated spatially. There is no direct interaction between the atoms. All the atoms interact with a single-mode of the cavity field. Quantum entanglement between the two atomic clusters is investigated for various initial states of the two atomic clusters and the field. When the cavity field is initially in a Fock state, we find that the time evolution of entanglement quasi-periodically oscillates regardless of the initial states of atoms. The oscillation period increases as the initial photon number increases. When all the atoms in both of the atomic clusters are initially in the excited state, we show that there is no entanglement between the atomic clusters with NA = NB = 1 regardless the initial state of the cavity field. However, when either NA or NB is larger than one, we find that the entanglement always exists even for a strong thermal field. In cases with different initial states of the atomic clusters, we notice that the entanglement becomes stronger as number of the atoms increases. When all the atoms in both of the clusters in the ground state, we also find that the entanglement can be enhanced even by a thermal field. We also notice that a single qubit can be entangled with multi-atoms which are initially in the ground state by the cavity field initially being in vacuum, thermal, coherent, and squeezed states.     

高Q腔中原子内态布居对原子平移运动的影响

基于原子作双光子共振跃迁的原子－场缀饰态，讨论了驻波腔场中两能级原子的量子化平移运动与原子内态布居间的相互影响，结果表明原子平移运动敏感地依赖于原子的内态布居，特别当原子处于两内态等权重同相位叠加态时，平移运动呈现出很稳定的特征。     

Measuring statistical characteristics of a quantized mode in various photodetection regimes

We develop a theory of the discrete photodetection model where individual unexcited atoms from the atomic beam passing through a cavity are used as pointers. Atomic energy state selective detectors (ionization chambers) measure the escape statistics of ground-or excited-state atoms. Mandelstam’s method of successive indirect quantum measurements underlies the theory being developed. In contrast to the available works, the suggested approach takes into account the atomic beam statistics, the operation nonideality (quantum efficiencies) of ionization chambers, the detector recovery time, the back action of the probe on the quantized mode, and the relaxation process in the time interval when the cavity is empty (without atoms). We derive formulas that relate the a posteriori probabilities of photodetector clicks to the elements of the main diagonal of the initial density matrix for the cavity mode. Our numerical simulations confirm that the inverse problem of reconstructing the initial photon number distribution in a cavity can be solved using the statistics of detector clicks measured during the transient process.