Spectral detection of resonance fluorescence as a generalized quantum measurement

Spectrally resolved detection of single atom resonance fluorescence in the limit of well-separated spectral lines is considered. By using a special type of correlation measurements over the fluorescent field, in which a filtered photon detection is followed by an unfiltered photon detection, we obtain a conditioned atomic state following the filtered photon detection. The properties of the atomic state following detection of the reflected photon are studied and interpreted on the basis of quantum interference between the dressed states. Measurement operators associated with the detection of the passed and reflected photons are derived and used to construct the master equation for the atomic density matrix subjected to continuous spectral detection, the filter tuning being arbitrary.     

单个原子的二模有效Raman理论研究

研究了单个原子或离子与两束激光量子场相互作用的非线性系统．首先提出描述一次涉及2k（k=1，2，3，…）个光子的光强相关耦合Raman过程的普适模型，然后利用作者发展的一种求解各种非线性Jaynes-Cummings模型的系统方法，精确求解了该普适模型，得到了它的能量本征值和本征矢、演化算符、光子数算符和原子反转算符的解析表达式 关键词：     

Polarization fields in the positronium atom undergoing emission or absorption of optical photons

This paper solves the problem of the interaction of an electron and positron via the field of soft and hard photons with emission or absorption of a real photon. The interaction is interpreted as a third-order QED effect in the coordinate representation. The role of intermediate states with positive and negative frequencies is studied. A general expression is derived for the matrix elements of the operator of the effective electron-positron interaction energy for different types of quantum transitions. The expression makes it possible to calculate the probabilities of the corresponding transitions in the nonrelativistic approximation. Electric dipole transitions in the positronium atom accompanied by emission (absorption) of an optical photon are investigated. Two-particle wave functions of the positronium atom are used to introduce the concept of polarization fields inside the positronium atom. It is found that the polarization fields depend on the coordinates and time and on the choice of the pair of states between which a quantum transition with emission or absorption of a photon takes place. Zh. éksp. Teor. Fiz. 113, 471–488 (February 1998)     

Atom-photon entanglement in the system with competing k-photon and l-photon transitions

We have investigated the evolution of the atomic quantum entropy and the entanglement of atom-photon in the system with competing k-photon and l-photon transitions by means of fully quantum theory, and examined the effects of competing photon numbers （k and l）, the relative coupling strength between the atom and the two-mode field （A/g）, and the initial photon number of the field on the atomic quantum entropy and the entanglement of atom-photon. The results show that the multiphoton competing transitions or the large relative coupling strength can lead to the strong entanglement between atoms and photons. The maximal atom-photon entanglement can be prepared via the appropriate selection of system parameters and interaction time.     

Spectra induced by interactions of atoms with ultrashort electromagnetic pulses

An ultrashort pulse of an electromagnetic field incident on an atom shakes the atom and gives rise to various electron transitions in it. These processes are accompanied by the reemission of the incident ultrashort pulse. This paper studies the relation between the spectra of reemitted photons of an ultrashort pulse and the transitions of atomic electrons into particular states. The obtained partial reemission spectra can allow one to relate direction patterns to the probability of the excitation of an atom into different states.     

虚光场在原子的周期衰变和回复效应中的影响

本文利用非相对论量子电动力学理论, 研究了在旋波近似(R w A ) 和非旋波近似下与双光子场作用的二能级原子算符的时间演化规律, 通过数值法和解析法论证了虚光场是原子的周期衰变和回复呈现量子噪声的根源, 并且说明了可忽略虚光场对回复时间影响的原因. 关键词：     

Polarization bremsstrahlung in α decay

A mechanism of formation of electromagnetic radiation that accompanies α decay and is associated with the emission of photons by electrons of atomic shells due to the scattering of α particles by these atoms (polarization bremsstrahlung) is proposed. It is shown that, when the photon energy is no higher than the energy of K electrons of an atom, polarization bremsstrahlung makes a significant contribution to the bremsstrahlung in α decay.     

虚光场在原子的周期衰变和回复效应中的影响

本文利用非相对论量子电动力学理论,研究了在旋波近似(RWA)和非旋波近似下与双光子场作用的二能级原子算符的时间演化规律,通过数值法和解析法论证了虚光场是原子的周期衰变和回复呈现量子噪声的根源,并且说明了可忽略虚光场对回复时间影响的原因。     

Continuous-Variable Entanglement Generation from a Four-State Atom under Raman Excitation

We investigate the generation and the evolution of continuous-variable (CV) entanglement from a laser-driven four-state atom inside a doubly resonant cavity under Raman excitation. Two transitions in the four-state atom independently interact with the two cavity modes, while two other transitions are driven by coupling laser fields. By including the atomic relaxation as well as cavity losses, we show that the CV entanglement with large mean number of
photons can be generated in our scheme. We also show that the intensity of the coupling laser fields can influence effectively the entanglement period of the cavity field. Different from the conventional resonant excitation scheme where zero one-photon detuning are required, it is found that the intensity and period of entanglement between the two cavity modes as well as the total mean photon number of the cavity field can be adjusted by properly
modulating the frequency detuning.     

Study of Some Properties of Two-Level Atom in Quantum Optics

With the concept of negative photon and the K-photon J C model, we investigate analytically the effect of virtual photon field on the collapse revival effect of atomic inversion and squeezing of atom, we find that there is a significant effect of virtual photon field on atomic inversion and squeezing of atom; with the one-photon model as an example, we find that the squeezing of atom occurs periodically, the time and times of squeezing are only related to the resonance frequency and the amplitude of squeezing related to coupling constant of atom field, mean photon number and resonance frequency; also we show that the effect of squeezing of atom does not exist within rotating wave approximation if K≥3. Taking the approach of nearest-neighboring spectrum in the quantum chaos field, we investigate the properties of energy spectrum in one-photon JC model and show that the integrable region,non-integrable region and transition region of this system can be illustrated by a phase diagram;also we discuss the influence of interaction of atoms on spectrum and Δ₃ statistics of adjacent energy levels, we find that the influence of interaction is little obvious in strong field but takes great important role in weak field.     

Superradiant cascade emissions in an atomic ensemble via four-wave mixing

We investigate superradiant cascade emissions from an atomic ensemble driven by two-color classical fields. The correlated pair of photons (signal and idler) is generated by adiabatically driving the system with large-detuned light fields via four-wave mixing. The signal photon from the upper transition of the diamond-type atomic levels is followed by the idler one which can be superradiant due to light-induced dipole–dipole interactions. We then calculate the cooperative Lamb shift (CLS) of the idler photon, which is a cumulative effect of interaction energy. We study its dependence on a cylindrical geometry, a conventional setup in cold atom experiments, and estimate the maximum CLS which can be significant and observable. Manipulating the CLS of cascade emissions enables frequency qubits that provide alternative robust elements in quantum network.     

Influence of the virtual photon field on the squeezing properties of atom laser

This paper investigates the squeezing properties of an atom laser without rotating-wave approximation in the system of a binomial states field interacting with a two-level atomic Bose--Einstein condensate. It discusses the influences of atomic eigenfrequency, the interaction intensity between the optical field and atoms,parameter of the binomial states field and virtual photon field on the squeezing properties. The results show that two quadrature components of an atom laser can be squeezed periodically. The duration and the degree of squeezing an atom laser have something to do with the atomic eigenfrequency and the parameter of the binomial states field, respectively. The collapse and revival frequency of atom laser fluctuation depends on the interaction intensity between the optical field and atoms. The effect of the virtual photon field deepens the depth of squeezing an atom laser.     

Quantum Teleportation and Resonance Information Transfer from One Atom to Another at Arbitrary Interatomic Distances

The feasibility of resonance transfer of quantum information from one double-level atom to another that is at an arbitrary distance from the former one has been proved. Symmetric and antisymmetric combinations of the wave functions of individual atoms are considered. When taking into account the interatomic dipole–dipole interaction, a certain energy corresponds to each wave function. A solution has been found to a system of equations for the amplitudes of the probability that a resonance photon will be absorbed by one of the system atoms, and it has been shown that the interaction of the system with actual photons has the result that the wave function of the final state of the system can be represented as a linear combination of the functions < 00|, < 0n|, and < n0| corresponding to the ground and excited states of individual atoms. The amplitude of the probability of each of these states depends on the interatomic distance and on the parameters of the action of actual photons on atoms. Three types of solution to the system of equations have been investigated for the resonance and nonresonance absorption of photons and different interatomic distances. It has been shown that when atoms are at an infinite distance from one another, so that there is no dipole–dipole interaction of atoms, quantum information can be transferred from one atom to another with a characteristic time considerably shorter than the time it takes for a photon to cover the interatomic distance. This effect is referred to as the effect of quantum teleportation in a system of resonance atoms.     

虚光场效应对原子激光压缩性质的影响

在压缩真空态光场和二能级原子玻色-爱因斯坦凝聚体相互作用系统中, 应用全量子理论, 分别在旋波近似和非旋波近似下, 研究了原子激光的压缩特性以及原子本征频率、光场-原子的耦合系数、光场初始压缩因子以及虚光场对原子激光压缩特性的影响. 研究表明,原子激光的两个正交分量均可被周期性压缩,原子的本征频率决定了原子激光两个正交分量涨落的量子Rabi频率,光场与原子的耦合系数决定了原子激光正交分量涨落的崩塌-回复振荡频率,当光场初始压缩因子增大和考虑虚光场效应时,原子激光正交分量的压缩深度均加深. 关键词： 玻色-爱因斯坦凝聚 压缩真空态 原子激光 虚光场效应     

克尔介质中皮秒亮孤子多光子J-C模型粒子数反转特性

利用全量子理论研究了克尔介质中皮秒孤子光场与二能级原子多光子相互作用系统中粒子数反转随时间的变化特性,用MATLAB软件编程模拟并讨论了初始平均光子数、克尔介质与场模非线性相互作用强弱、孤子光场与原子耦合强度及相互作用过程中跃迁光子数目对粒子数反转的影响.数值计算结果表明：初始平均光子数越大、克尔介质与场模的非线性相互作用越强、孤子光场与原子耦合强度越小或相互作用过程中跃迁光子数目越多,粒子数反转崩坍与恢复的振荡幅度越小、平均值越大.     

四模场中单原子系统的新算符求解方法

提出处理腔场与原子、腔场与腔场等系统的较为一般算符方法。基于此方法,通过构造四对时间依赖的产生和湮灭算符,简捷地求解四模腔场或四腔场与二能级原子非共振相互作用系统,得到其本征态、本征值和一般态矢。特别地,在四模场或四腔场和原子的初态分别为真空态和一般叠加态时,给出四场模平均光子数和原子布居数反转的时间演化。该新方法可应用于其它一些量子系统。     

Photon,quantum and collective,effects from rydberg atoms in cavities

I review some theories of the interaction ofN Rydberg atoms interacting collectively with radiation in microwave cavities. The radiation may be incoherent (black body) radiation or it may be coherent. In the former case theories of the steady state inversion and of the superradiance from initially inverted atoms in low-Q cavities agree well with experimental observations. In the latter case in low-Q cavities ‘phase transitions’ of both first and second order types are predicted and should be observable by monitoring the output of an atomic beam by an atomic ionisation detector. The first order transition which occurs at opposite detunings of the cavity and atoms from the frequency of the coherent driving field is of “optically” bistable type but hysteresis is suppressed by quantum fluctuations which can be large in the cavity field close to the transition. I also review a theory of the spectra from single atoms in cavities ofarbitrary Q containing a few microwave photons. A transition from a single peaked Lorentzian spectrum at low-Q to a double-peaked spectrum forQ≃10⁶ is predicted and peaks representing one or more photon transitions of the Jaynes-Cummings model are also expected to be observable at these or largerQ values. The collective theories are all based onN atom Dicke type models driven by the coherent or incoherent field. Substantial squeezing of the fluorescent radiation field from these Dicke models is also predicted and may be observable with Rydberg atoms.     

Peak structure of polarized bremsstrahlung upon scattering by coupled atomic electrons

Peculiarities of polarized bremsstrahlung (PB) of relativistic electrons produced upon scattering by coupled atomic electrons are discussed; in this case, PB is regarded as scattering of virtual photons of the electromagnetic field of a fast charge by atomic electrons with their coupling taken into account. In this case, the atomic electron during scattering can acquire recoil energy only through separate portions, as a result of which the spectrum of scattered photons degenerates into a series of narrow peaks.     

纠缠相干态光场驱动下∧-型三能级原子的辐射谱

采用时间演化算符方法,研究∧-型=三能级原子与纠缠相干态光场共振相互作用的辐射谱.给出了辐射谱一般公式,并讨论在纠缠相干态光场驱动下的辐射频谱结构.结果表明,无论下能级简并与否纠缠相干态光场平均光子数很小时均出现拉比分裂,且强度随双模光场纠缠程度的增加而增加.当两下能级简并时,若两模场的平均光子数较小,辐射谱呈现对称多峰结构,若两模场的平均光子数较大,辐射谱呈现对称五峰结构.当两下能级非简并时,若两模场的平均光子数较小,辐射谱呈现对称多峰结构.若两模场的平均光子数较大,辐射谱呈现对称十峰结构.纠缠相干光与非纠缠相干光辐射谱的本质差别有两点:一是双模光场强量子关联导致纠缠度越强拉比峰强度越高;二是存在纠缠时由于两模场相干性导致辐射谱呈现对称多峰结构.