The problem of two electrons in an external field and the method of integral equations in optics

This paper solves the problem of the interaction, via the field of virtual photon field with the emission or absorption of a real photon, of two atomic electrons located at arbitrary distances from one another. 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-electron interaction energy for different types of quantum transitions. The expression makes it possible to calculate the probabilities of the corresponding transitions and to examine various patterns of induction of polarizing fields by one atom at the point occupied by the other atom. The exchange of virtual photons between the atoms located at arbitrary distances from one another is shown to lead to additional terms in the operators of spin-orbit and spin-spin coupling of the atomic electrons, over and above those in the corresponding Breit operators. It is shown that there is an important difference between the induction of polarizing fields and the transfer of optical photons. In particular, it is found that when polarizing fields are induced, a situation may arise in which the disappearance (production) of a photon takes place at the point occupied by one atom, while absorption (emission) of the same photon occurs at the place occupied by the other atom. A block diagram of an experimental device that could be used to study this property of polarizing fields is presented. Finally, a method of deriving integral field equations is proposed. The method is based on allowing for polarizing fields, and its effectiveness is demonstrated by the example of electric dipole and spin transitions in the spectrum of interacting atomic electrons. Zh. éksp. Teor. Fiz. 114, 1555–1577 (November 1998)     

Photon-assisted electronic structure and transport for a quantum dot

This paper investigates theoretically the electronic structure and transport of a two-level quantum dot irradiated under a strong laser field at low temperatures. Using the method of Keldysh equation of motion for nonequilibrium Green functions, it examines the time-averaged density of states and conductance for the system with photon polarization parallel with and perpendicular to the tunnelling current direction respectively. It is demonstrated that, by analysing some numerical examples, more photon sidebands resonance states and multi- and single-photon transitions are found when diagonal matrix elements dominate the interaction, while the electronic transitions due to multiphoton absorption are more or less suppressed when off-diagonal interaction dominates.     

The positronium atom as a benchmark for Rydberg excitation experiments in atomic physics

Positronium is a hydrogen-like pure leptonic atom that has gained great attention in basic physics for its role in antimatter studies, in quantum electrodynamics tests and in material science. Positronium spectroscopy is also an interesting research field, especially in the again unexplored region of Rydberg states, where motional effects turns out of overwhelming importance in determining the level structure, at variance with the usual Rydberg atomic spectroscopy. In this paper we present a simple theory of optical excitation of positronium high-n levels in strong magnetic fields, and determine the conditions for obtaining saturation of the transitions. It is shown that positronium atom can be an atomic physics benchmark for laser excitation experiments on Rydberg states in magnetic environments.     

A phase formalism for excitonic transitions

We develop a matrix formalism for the phase involved in quantum transitions experienced by excitons on the basis of the quantum mechanics of the hydrogen atom. Both photon emission and absorption within the context of the above transitions are modelled.     

Inelastic processes and interference effects during the interaction of positronium with ultrashort electromagnetic pulses

The excitation, breakup, and reradiation during the interaction of a positronium atom with ultrashort electromagnetic pulses are considered. The probabilities of inelastic processes and reradiation spectra have been obtained. The interference between the amplitudes of the photon emission by the electron and positron is shown to contribute noticeably to the reradiation spectra. The developed approach is applicable for describing the interaction of positronium with ultrashort pulses of attosecond or shorter duration.     

Photon Emissions from a Spinor Bose–Einstein Condensate of Positroniums

We investigate the quantum dynamics of the decay of a multiple-component positronium condensate into pairs of photons. A positronium atom has four internal spin states which are interconvertible through s-wave interactions. The quantum fields of all spin states of positroniums and photons are simulated from first principle in quasi-one-dimensional system using the truncated Wigner method. This method warrants us a full treatment of the depletion of positronium fields and the spin mixing induced by s-wave collisions between positronium atoms. Particularly,it yields the momentum spectrum of the emitted photons and the photon-photon correlations.     

On the quantum link for transport of logic states

A novel approach for representing logic states in the quantum nodes and transferring the states from one node to another is proposed. Both transmit and receive nodes consist of a rubidium atom (⁸⁷Rb) placed at the center of a two-mode cavity. Representation of logic states by two subspaces of the space of ⁸⁷Rb atom hyperfine states eliminates the need for the transmitting node to change logic state during logic transfer through Raman process. The atom is excited by simultaneous application of two laser beams - one for each subspace. Based on the logic state, the atom emits a photon of appropriate frequency and polarization through Raman process within the corresponding subspace. The emitted photon leaks out of the cavity, reaches the receiving node, and initiates logic dependent transitions there. A simulation platform is developed through the system Hamiltonians for transmit and receive nodes followed by the formulation of the time evolution of the density matrices for the nodes. The efficacy of the simulation approach is emphasized.     

在五能级三重∧型原子系综中利用暗态极化子理论制备W态(英文)

在由三个经典控制场驱动的五能级三重(?)型原子系综与三个多模量子光场相互作用的系统中,得到了该系统的极化子.利用求得的极化子结果研究了光量子态存储到原子激发态,或从原子系综中释放出光量子信息.在释放过程中,通过绝热调节控制场的Rabi频率,能得到纠缠光子态.尤其是在一定条件下,能利用该系统能制备一类W态,这类态在量子信息处理中有潜在的应用.     

High quantum efficiency of intersubband transitions in coherent tunneling of electrons through asymmetric double-barrier structures

A converging perturbation series that can be summed analytically has been obtained for intersubband transitions of electrons coherently tunneling through the middle of a dimensionally quantized level in an asymmetric double-barrier structure in a high-frequency terahertz electric field. The possibility of a substantial increase in tunneling current accompanied by either absorption or emission of a photon has been demonstrated. The quantum efficiency of radiative transitions between dimensionally quantized levels can be up to 66%. Zh. éksp. Teor. Fiz. 112, 237–245 (July 1997)     

Exact wave functions for atomic electron interacting with photon fields

Many nonlinear quantum optical physics phenomena need more accurate wave functions and corresponding energy or quasienergy levels to account for. An analytic expression of wave functions with corresponding energy levels for an atomic electron interacting with a photon field is presented as an exact solution to the Schrödinger-like equation involved with both atomic Coulomb interaction and electron-photon interaction. The solution is a natural generalization of the quantum-field Volkov states for an otherwise free electron interacting with a photon field. The solution shows that an Nlevel atom in light form stationary states without extra energy splitting in addition to the Floquet mechanism. The treatment developed here with computing codes can be conveniently transferred to quantum optics in classical-field version as research tools to benefit the whole physics community.     

Quantum effects in submillimetre hot hole semiconductor lasers

The hole dynamics and emission processes in degenerate band semiconductors in strong crossedE B fields were studied both theoretically and experimentally. The Luttinger effective mass Hamiltonian was used to study the Landau level energy spectrum in anisotropic valence bands of Ge. The dependence of the energy spectrum onE,H fields orientation is analysed. The role of quantum effects, such as interaction and mixing of light and heavy hole states in the scattering process and Landau level population is studied. The results of experimental studies of stimulated emission spectra for intersub-band and cyclotron transitions as well as their dependence onE,H field orientation are presented, the experimental data being in good agreement with the quantum model calculations.     

Spin polarization dependent optical transition rates observed in the integer quantum Hall region

We report on a field-dependent photoluminescence (PL) emission rate for the transitions between band states in modulation-doped CdTe/Cd_1−xMg_xTe single quantum wells in the integer quantum Hall region. The recombination time observed for the magneto-PL spectra varies in concomitance with the integer quantum Hall plateaus. Furthermore, different PL decay times were observed for the two circular polarizations, i.e. for the transitions between the Zeeman split subbands of the Landau levels. We analyzed the data in comparison with the experimentally determined spin polarization of the conduction electrons and the Zeeman splitting of the valence band. Furthermore, we discuss the relevance of the spin polarization of the conduction electrons, the electron–hole exchange interaction and the spin-flip processes of the hole states for the PL decay time.     

Radiative properties of diamagnetic levels in atoms: Dependence of transition probability on magnetic field strength

We study the effect of diamagnetic interaction on the probability of radiative transitions of an atom from states split by a field. We write the analytic expressions for the diamagnetic corrections to the matrix elements of transitions belonging to the Lyman and Balmer series and of transitions between arbitrary nondegenerate states in hydrogen. We also discuss the perturbation theory for transitions from degenerate diamagnetic states. The theory is based on expanding in powers of the field strength the eigenfunctions and eigenvalues of the matrix of diamagnetic interaction in the subspace of states with given principal and magnetic quantum numbers. The field changes the coefficients in both the superposition and the degenerate basis. To derive the analytic expressions for the higher-order matrix elements, we use the Sturm expansion of the reduced Coulomb Green’s function. We also elaborate on the features of the frequency dependence of the corrections to the radiative matrix elements, which correlate with the structure of the diamagnetic spectrum of excited levels. Finally, we establish that the magnetic field acts selectively on the diamagnetic components of emission lines: as the field strength increases, an increase in the intensity of certain lines is accompanied by a decrease in the intensity of the other lines. Zh. éksp. Teor. Fiz. 116, 1161–1183 (October 1999)     

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.     

Intersublevel transitions in self-assembled quantum dots

Intersublevel transitions in semiconductor quantum dots are transitions of a charge carrier between quantum dot confined states. In InAs/GaAs self-assembled quantum dots, optically active intersublevel transitions occur in the mid-infrared spectral range. These transitions can provide a new insight on the physics of semiconductor quantum dots and offer new opportunities to develop mid-infrared devices. A key feature characterizing intersublevel transitions is the coupling of the confined carriers to phonons. We show that the effect of the strong coupling regime for the electron–optical phonon interaction and the formation of mixed electron–phonon quasi-particles called polarons drastically affect and control the dynamical properties of quantum dots. The engineering of quantum dot relaxation rates through phonon coupling opens the route to the realization of new devices like mid-infrared polaron lasers. We finally show that the measurement of intersublevel absorption is not limited to quantum dot ensembles and that the intersublevel ultrasmall absorption of a single quantum dot can be measured with a nanometer scale resolution by using phonon emission as a signature of the absorption. To cite this article: P. Boucaud et al., C. R. Physique 9 (2008).     

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。     

Elementary defects in graphane

We propose a novel approach for spectroscopic characterization of quantum systems. A superconducting quantum system—an artificial atom—is coupled asymmetrically to two open-end transmission lines (1D half-spaces). The lines themselves are strongly decoupled from each other. This results in suppression of the direct microwave propagation from one side to another. The atom, excited from the weaker coupled side relaxes with photon emission preferably to the stronger coupled side. By measuring the emission spectrum, we reconstruct the energy levels of the artificial atom. Our method allows to reject the excitation tone and to detect only the elastically scattered emission corresponding to intra-atomic transitions. We also demonstrate visualization of the higher-level transitions by populating the excited levels. Such a system does not have an optical analog with natural atoms or quantum dots coupled to two half spaces.     

Quantum Computation and Entangled-State Generation Through Photon Emission and Absorption Processes in Separated Cavities

We propose a scheme to implement a two-bit conditional quantum phase gate and generate a multi-atom cluster state and a two-atom three-dimensional entangled state based on photon emission and absorption processes. In the scheme, a Λ-type atom and a V-type atom are individually trapped in two spatially separated cavities connected by an optical fiber. By choosing the interaction time and the ratio of coupling parameters appropriately, the gate operation and entanglement generation can be determinately achieved. We also discuss the influence of photon Leakage on the fidelities of the gate and entanglement and show that the scheme is scalable and feasible in the experimental realization and further utilization.     

Multiphoton analysis of the free electron laser

A model of the free electron laser is proposed which is based on the classical current of the electron in the wiggler field interacting with a quantized radiation field. To calculate the gain, the quantum recoil for the processes of n-photon emission and absorption must be put in by hand from kinematical considerations. Apart from a spontaneous emission term the gain agrees essentially with the usual small signal expression, for the radiation field being in either an eigenstate of photon number or in a coherent state. The distribution of the electrons after the interaction is, however, essentially quantum mechanical.