Changes in quantum states of atoms in a markovian thermostat

We solve the nonlinear Schrödinger equation, taking into account self-interaction through the surrounding medium. We have found that such atoms have a countable set of stable equilibrium states, coinciding with the wave eigenfunctions of an individual atom. We show that transitions of an atom from equilibrium quantum states corresponding to less excited levels to more excited levels occur in jumps, while transitions from equilibrium states corresponding to upper levels to lower levels may occur either as radiationless transitions or be accompanied by spontaneous emission at the eigenfrequency of the quantum transition. We have found the conditions for which a change in the topological structure of the atomic wavefunction is possible.     

Spontaneous emission spectrum of a three-level atom embedded in photonic crystal

The two models of three-level (one upper level and two lower levels, or two upper levels and one lower level) atom embedded in a double-band photonic crystal are adopted. The atomic transitions from the upper levels to the lower levels are assumed to be coupled by the same reservoir which are respectively the isotropic photonic band gap (PBG) modes, the anisotropic PBG modes and the free vacuum modes. The effects of the fine structure of the atomic ground state levels in the model with one upper level and two lower levels, and the quantum interferences in the model with two upper levels and one lower level on the spontaneous emission spectrum of an atom are investigated in detail. Most interestingly, it is shown that new spontaneous emission lines are produced from the fine splitting of atomic ground state levels in the isotropic PBG case. The quantum interferences induce additional narrow spontaneous lines near the transition from the empty upper level to the lower level.     

Emission of excited copper atoms in laser-produced erosion plasmas

The distribution of emission from excited states of a copper atom in erosion plasmas formed in vacuum by the action of neodymium laser pulses with a power density of (3–5)×10⁸ W/cm² on a copper target is studied. Averaged spectra and oscillograms of emission of Cu I lines were recorded in a region of 210–600 nm. Resonant lines of Cu I, lines of cascade transitions to resonant levels of Cu I, and lines from shifted levels of a copper atom are shown to possess the highest intensity. Oscillograms of emission at Cu I transitions have two peaks, which may be associated with two phases of surface evaporation of copper: under the action of a Nd³⁺:YAG laser pulse and radiation of the core of an erosion plasma plume. The relationship between the intensities of peaks in oscillograms of emission of Cu I lines points to the presence of a considerable cascade contribution to the population of the resonant states of Cu I and self-absorption of resonant lines of a copper atom at the first stage of evaporation of a copper target.     

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)     

Effect of atomic initial phase difference on spontaneous emission of an atom embedded in photonic crystal

<正>We investigate the effect of initial phase difference between the two excited states of a V-type three-level atom on its steady state behaviour of spontaneous emission.A modified density of modes is introduced to calculate the spontaneous emission spectra in photonic crystal.Spectra in free space are also shown to compare with that in photonic crystal with different relative positions of the excited levels from upper band-edge frequency.It is found that the initial phase difference plays an important role in the quantum interference property between the two decay channels.For a zero initial phase,destructive property is presented in the spectra.With the increase of initial phase difference,quantum interference between the two decay channels from upper levels to ground level turns to be constructive.Furthermore, we give an interpretation for the property of these spectra.     

230—245nm范围内Cl原子共振增强多光子电离光谱

利用共振增强多光子电离－－时间飞行质谱技术获得了Ｃｌ原子在２３０－２４５ｎｍ范围内的代振增强多光子电离光谱,共观察到２６条谱线,其中５条是作者新观察到的,这些谱线对应从Ｃｌ原子基态到激发态的双光子跃迁。从中还观察到Ｃｌ原子在强电场中的Ｓｔａｒｋ效应,发现在强场条件下,Ｃｌｄ原子绵基太＾２Ｐ１／２＾０和＾２Ｐ３／２＾０两能级之间的能工位移１．３５ｃｍ＾＝１。而各电子激发态的Ｓｔａｒｋ位移则大致相等,     

利用破坏对称性的超导人造原子制备χ型四比特纠缠态

提出了利用在一维传输线共振器中的破坏对称性的超导人造原子来制备χ型四比特纠缠态的方案. 方案中所用到的Δ型三能级人造原子不同于自然的原子, 它可以产生循环跃迁. 经过适当时间的相互作用和简单的操作, 可以得到想要制备的纠缠态. 由于人造原子的激发态和光子态被绝热消除, 所以该方案对于人造原子的自发辐射和传输线共振器的衰减是鲁棒的.     

Large index of refraction without absorption via decay-induced coherence in a three-level V system

We study the effects of quantum interference from spontaneous emission on the dispersion-absorption properties in a three-level V-type atomic system with two near-degenerate excited levels. We found that due to the quantum interference between two spontaneous decay channels, large index of refraction without absorption always can be obtained just by choosing proper values of the relative phase between the two applied fields.Received: 27 February 2004, Published online: 26 May 2004PACS: 42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption - 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift     

Control of Spontaneous Emission from a Microwave Field Coupled Five-Level M-type Atom in Photonic Crystals

We investigate the spontaneous emission spectrum of a five-level M-type atom driven by a microwave field, in which one lower level is coupled by the same modified reservoir to two upper levels. The results show that a few interesting phenomena in spontaneous emission spectra, such as spectral-line shift, spectral-line enhancement and spectral-line suppression, which can be controlled by adjusting the proper parameters of the system. These phenomena can originate from quantum interference of the strong coupling system.     

Influence of detuning on the spontaneous emission of a driven four-level atom embedded in photonic crystals

We study the spontaneous emission of a four-level atom with two transitions coupled to a reservoir that has a photonic bandgap near the band edge. Moreover, the transition from the upper level to an auxiliary level is driven by a laser. Considering the different detuning of the external driving field, we discuss some effects, such as a laser-induced dark line, a laser-induced line splitting, and a laser-induced pushing of a dressed state out of the bandgap, which originate from the quantum interference effect and control of the external driving field.     

Dynamics of coherent and incoherent emission from an artificial atom in a 1D space

We study dynamics of a two-level superconducting quantum system, analogous to a natural atom in an open space, by measuring the evolution of its coherent and incoherent emission. The emitted waves containing full information about the states of the artificial atom are efficiently collected due to strong atom-transmission-line coupling. This allows us to do simultaneous measurements of all the quantum state projections and perform a full characterization of the system. We derive coherence times and extract the two-time correlation function from the dynamics of the coherent emission.     

Modification of spontaneous emission from a five-level M-type atom in coupled cavity waveguide

We study the spontaneous emission spectrum of a five-level M-type atom driven by a microwave field, in which two upper levels are coupled by the same-coupled cavity waveguide reservoir to a lower level. The spectrum behavior presents a strong non-Lorentzian shape that originates from effective quantum interference in Markovian reservoir, in which the spectral line can be significantly enhanced and eliminated by adjusting the proper parameters of the system. However, for non-Markovian reservoir, it seems that the shape of emission spectrum is quite dependent on the geometry behavior of a coupled cavity waveguide.     

Intra-acceptor hole relaxation in Be δ-doped GaAs/AlAs multiple quantum wells

This paper studies the dynamics of intra-acceptor hole relaxation in Be δ -doped GaAs/AlAs multiple quantum wells (MQW) with doping at the centre by time-resolved pump-probe spectroscopy using a picosecond free electron laser for infrared experiments. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of the Be acceptor from the ground state to the first three odd-parity excited states respectively. The pump-probe experiments are performed at different temperatures and different pump pulse wavelengths. The hole relaxation time from 2p excited state to 1s ground state in MQW is found to be much shorter than that in bulk GaAs, and shown to be independent of temperature but strongly dependent on wavelength. The zone-folded acoustic phonon emission and slower decay of the wavefunctions of impurity states are suggested to account for the reduction of the 2p excited state lifetime in MQW. The wavelength dependence of the 2p lifetime is attributed to the diffusion of the Be atom δ -layer in quantum wells.     

Spontaneous emission spectrum of a four-level atom in a double-band photonic crystal

The spontaneous emission spectrum from a four-level atom in a double-band photonic crystal has been investigated.We use the model which assumes three atomic transitions. One of the transitions interacts with the free vacuum modes,and the other two transitions couple to the modes of the isotropic photonic band gap (PBG), the anisotropic PBG and another free vacuum. The effects of the fine structure of the lower levels on the spontaneous emission spectrum of an atom are investigated in detail in the three cases. New features of four (two) transparencies with two (one) spontaneous emission peaks, resulting from the fine structure of the lower levels of an atom, are predicted in the case of isotropic PBG modes.     

双带型光子晶体中双V型四能级原子自发辐射谱中的黑线研究

研究了双带型光子晶体中双V型四能级原子自发辐射的辐射谱.双V型四能级原子同时与真空热库和双带型光子晶体热库耦合.研究发现双V型四能级原子自发辐射谱中有三种不同原因可能引起的黑线：第一种是由于量子干涉效应;第二种是由于各向同性光子晶体带边处态密度具有奇异性;第三种是真空场中的量子干涉和光子晶体禁带内态密度为零共同作用的结果.通过移动光子晶体的带边位置,在各向同性光子晶体带边引入光滑因子,以及在光子晶体中引入缺陷等对这三种黑线的影响,对上述结果进行了分析和讨论. 关键词： 双带型光子晶体 双V型四能级原子 黑线     

INFLUENCE OF ATOMIC MOTION ON SPONTANEOUS EMISSION FROM A THREE-LEVEL ATOM

本文研究了V型三能级原子的自发辐射谱。如果不考虑原子的质心运动,则自发谱中有一暗线,这是干涉所致。如果考虑原子的质心运动,则暗线消失,即原子的质心运动破坏了干涉效应。     

Subject index to volume 33

We have simulated the Gibbs-Vrehen-Hikspoors observations of quantum beat superfluorescence (SF) from the 7P→7S transitions in Cs vapour by extending the previous numerical work on semi-classical 2-level atom SF to particular 3-and 4- level atom models. Beats at the spacing of the two upper levels modulate the SF from a 3-level model consisting of two close upper levels sharing a common lower level. Lower state beats modulate the SF from a 4-level model consisting of two separated upper levels coupled independently to two lower levels. Results for the leading SF pulse are in good qualitative agreement with the experiments.     

二能级原子与高品质因子腔的自发辐射特性

用全量子理论研究二能级原子单模腔耦合系统,通过理论推导和数值计算得出系统的自发辐射光谱和平均粒子数密度.共振时腔与原子的发射光谱在强耦合与弱耦合区域有所不同,腔发射光谱分裂只出现于强耦合区域,而原子发射光谱由于腔感应透明效应在弱耦合区域出现了缺口.本文系统地研究了原子与腔在失谐时的发射光谱,在好腔机理(腔线宽小于原子线宽g)原子与腔即使在大失谐时腔发射出腔频率的光子,这给当前实验上困惑的特性提供了一个理论依据.为了给腔感应透明效应一个新的深入了解,还研究了原子与腔平均粒子数密度随时间的演化,以及平均粒子数密度与光强度之间的关系. 关键词： 自发辐射 强耦合 腔感应透明 好腔机理     

One- and two-photon resonance fluorescence of a three-level atom at high photon densities

We consider the possible physical processes that may arise in a three-level atom when only two of its levels interact with a strong electromagnetic field and when the atomic transition frequency is nearly equal to once and twice the frequency of the laser field, respectively. There have been found pronounced cooperative effects in the spectrum of the two-level system, which is in resonance with the laser field, arising from the presence of the third level. The excitation spectra describing the transitions from the first excited state into the second excited state and from that to the ground state consist, apart from the two central peaks, of two pairs of sidebands which are induced by the laser field of the neighbouring system. Detailed expressions of the spectral functions for the physical processes of one- and two-photon resonance fluorescence have been derived and discussed in the limit of high photon densities. The excitation spectrum of the low frequency modes has been considered and discussed in detail. It is found that quantum beats in spontaneous emission may appear in the spectra of the one- and two-photon resonance fluorescence arising from the interference between the two atomic transition frequencies and the frequency of the laser field. The importance of the low frequency modes that occur in the processes in question has been pointed out.     

Squeezing‐Enhanced Atom–Cavity Interaction in Coupled Cavities with High Dissipation Rates

The realization of the strong coupling regime is requisite for implementing quantum information tasks. Here, a method for enhancing the atom–field coupling in highly dissipative coupled cavities is proposed. By introducing parametric squeezing into the primary cavity, which is only virtually excited under specific parametric conditions, coupling enhancement between the atom and the auxiliary cavity is realized for appropriate squeezing parameters. This enables the system to be robust against large cavity decay and atomic spontaneous emission. The observation of vacuum Rabi oscillations show that the originally weakly coupled system can be enhanced into an effective strong coupling regime.