Electromagnetically induced transparency and slow light in a Λ-type three-level system of GaAs/AlGaAs multiple quantum wells

A Λ-type three-level system of GaAs/AlGaAs multiple quantum wells (MQWs) was constructed by using exciton spin coherence in the transient optical response. Theoretical analysis with density matrix and Maxwell equations then yielded the phase shift, absorption, group velocity and group velocity dispersion. The calculated velocity is ～6.14?×?10^4?m/s and the corresponding pulse delay is ～8?ps. A convenient basis is provided for investigating how many-body effects in semiconductors modify the magnitude, spectral shape, and space and time dependence of the electromagnetically induced transparency phenomenon.     

Emission spectrum of a Λ-type three-level atom driven by the squeezed coherent field and grey-body radiation field

Abstract

By means of quantum electrodynamics, an analytical expression of emission spectrum for a Λ-type three-level atom with the two non-degenerate lower levels in the cavity is given. The character of the emission spectrum for the input in pure number state, a squeezed coherent state and grey-body state are exhibited. The effects of the atomic initial state, the field property, the cavity absorptivity and the system temperature on the time-dependent physical spectrum are analysed.     

Diffusion of carbon and titanium in γ -iron in a magnetic field and a magnetic field gradient

The diffusion coefficients of carbon and titanium in γ -iron were measured in a 6T magnetic field and in magnetic field gradients ranging from 30 to 45 T/m. We have found that the diffusion of carbon in γ -iron is retarded by application of a 6T magnetic field. In contrast with carbon diffusion, no noticeable effect of a magnetic field on the diffusivity of titanium in γ -iron is observed. On the other hand, the diffusion of carbon in γ -iron can be enhanced in a magnetic field gradient when carbon atoms move towards the direction with a higher magnetic field strength. The higher the magnetic field gradient strength becomes, the more the carbon diffusion is enhanced. Nevertheless, a magnetic field gradient causes a decrease in diffusivity of carbon in γ -iron when the opposite magnetic field gradient is applied.     

Phase control of electromagnetically induced transparency in a double-Λ system

It is experimentally demonstrated that the effect of electromagnetically induced transparency (EIT) can be controlled through the radiation phases. Corresponding investigations are performed by exciting a sodium atomic vapour by four-frequency laser radiation in a double-Λ configuration. In such a system the nonabsorbing (dark) state, responsible for EIT, is created only for particular values of the relative radiation phase. This phase dependency is confirmed using three different methods of phase control. Additionally, the relative phase is set at defined values in order to adjust the medium to a fixed transmission behaviour.     

Heterodiffusion of aluminum in α-iron in a pulsed magnetic field

Using an X-ray diffraction technique, the coefficients of volume diffusion of Al in α-Fe at T = 730°C have been measured for the first time in a pulsed magnetic field with a pulse amplitude of 39.8–238.8 kA/m and a frequency of 1–8 Hz. It is established that both frequency and amplitude of magnetic field pulses significantly influence the diffusion process.     

Position-dependent absorption-dispersion spectrum of a Λ-type three-level atom embedded in a defective photonic crystal

The position-dependent optical spectra of a Λ-type three-level atom embedded in a photonic crystal are studied by considering the double-band photonic band gap reservoir with defect modes in the band gap. It is shown that the number of absorption peaks, transparency windows and the slope of the dispersion curve can be modulated by adjusting the position of the embedded atom.     

Spontaneously induced atom–radiation entanglement in an ensemble of trapped two-level atoms

Analysis of the effects of the spontaneously induced correlation on atom–radiation entanglement in an ensemble of two-level atoms initially prepared in the upper energy level and then trapped in a cavity containing a source of a squeezed radiation employing the method of evaluating the coherent-state propagator is presented. It is found that the cavity radiation exhibits squeezing which is directly attributed to the squeezed radiation initially present in the cavity. The intensity of the cavity radiation increases with the squeeze parameter and interaction time. It is also shown that a substantial degree of entanglement between the atomic state and radiation mode exits at a particular time which depends on the coupling constant and squeeze parameter. It is understood that although the squeezed radiation is directly accountable for the cavity squeezing, it significantly destroys the atom–radiation entanglement induced by the correlation between spontaneously emitted radiation and the atoms.     

The radiative characteristics and the decay properties of an excited Λ-type atom in anisotropic photonic crystals

The radiative characteristics and the decay properties of a Λ-type excited atom embedded in anisotropic photonic crystals are studied. It is found that the dynamic properties of the atom and the propagating characteristics of the emitted field are apparently influenced by the relative position of the upper level from the forbidden gap and the two lower levels. By Von Neumann measurement, the effects of measurements on the decaying atom are investigated. The frequent projection on the excited state can lead to decay suppression or an acceleration effect at rather low repetition rates, depending on the frequency of measurements and the relative position of the upper level from the photonic crystals band edge.     

Growth rates of Bénard-Marangoni convection in a fluid layer in the presence of a magnetic field

In this paper we analyze the effect of a uniform vertical magnetic field on the linear growth (and decay) rates of the steady Bénard-Marangoni instability in a horizontal layer of quiescent, electrically conducting fluid with a uniform vertical temperature gradient subject to a prescribed heat flux at its lower boundary. Explicit analytical expressions for the linear growth rates of long-waves instability modes are derived for the first time. The numerically-calculated linear growth (or decay) rates showing the stabilizing effect of the magnetic field are also presented.     

Confinement of energetic ions in a tokamak plasma at magnetic field in the range of 0.7–1.0 T

We have experimentally studied the influence of toroidal magnetic field (B _T) and plasma current (I _p) on the capture and confinement of energetic ions (EIs) formed upon ionization of a neutral beam injected in a tokamak. Based on the results of measurements of the flux of 2.45-MeV fusion neutrons, it is concluded that the amount of EIs significantly grows with increasing B _T from 0.7 to 1.0 T and Ip from 140 to 180 kA. In addition to the classical Coulomb slowing down, a supplementary channel of EI losses is found that accounts for a 15% decrease in their confinement time.     

Permanently disentangled states of atom–field system via spontaneously generated coherence

Abstract

The effect of spontaneously generated coherence on evolution of the entanglement between a driven four-level Y-type atom and its spontaneous emission field is studied. We have shown that the atom will be entangled to its spontaneous emission field due to spontaneously generated coherence and coherent population trapping at the steady state. It is found that the degree of entanglement strongly depends on the initial atomic state. So, it can be controlled by the pumping laser pulses used for preparing an initial atomic system. More interestingly, the atom–field system can be found in a permanently disentangled state for a properly prepared atom.     

Oscillatory behavior of photogenerated carrier diffusion in γ-Mo4O11 under magnetic field

The pulsed-laser induced transient thermoelectric effect (TTE) under electric and magnetic fields has been measured for the CDW material -Mo ₄O₁₁. The photo-induced TTE voltages decay with the characteristic relaxation times _i (i=2 and 3) for thermal diffusion of two types of holes. In the CDW state [Tc (=100 K)], the relaxation times _i oscillate periodically with the magnetic field, and the corresponding relaxation amplitudes a_i change stepwise at the minima in the _i-Bcurves. These oscillation periods B_i (=0.56–0.68 T) are independent of the electric field E, and these increase appreciably with temperature above 40 K, while the initial phase differences _i increase linearly with E.Possible mechanisms for such anomalous oscillations of the relaxation times are discussed from classical and conventional quantum mechanical viewpoints; however, its origin is uncertain at the moment.     

Can a repulsive potential in graphene have boundstates in a magnetic field?

We consider Klein tunneling through a repulsive and cylindrical potential with range R and strength V. Recently it was found that, in the strong coupling regime R/l < 1, the repulsive potential can have bound states peaked inside the potential with tails extending over l mean square root of 2(N+1), where N is Landau level (LL) index and f is the magnetic length. The presence of these bound states is a consequence of a subtle interplay between Klein tunneling and quantization effect of magnetic fields. Because of the presence of these bound states the effective coupling between the repulsive potential and an electron can be attractive. Here we show that this effect is a consequence of singular interaction between the repulsive potential and an electron that cannot be captured in perturbative approaches.     

Tunable double optomechanical induced transparency in an optomechanical system with Bose–Einstein condensate

We investigate the double optomechanically induced transparency (OMIT) of a weak problem field in a hybrid optomechanical system, composed of a Bose–Einstein condensate (BEC), a movable mirror and an optical cavity. Contrast to the single OMIT window in a traditional optomechanical system, the frequency difference between the BEC and the moving mirror in our system can lead to the splitting of the single OMIT window into two transparency windows. Interestingly, the splitting of the two windows varies near linearly with the frequency difference and is robust against the cavity decay. This property can be applied to detect the frequency of the movable mirror. Besides, the driving power and the BEC-cavity coupling strength play a key role in controlling the width of the two transparency windows.     

The segregated structure of MnBi in Bi–Mn alloy solidified under a high magnetic field

Influence of high magnetic field on segregation of BiMn grains during solidification of Bi–Mn alloy has been investigated. Experiment of melting and solidifying of the alloy in a 10 T magnetic field generated by superconductor magnet was conducted. An interesting phenomenon was found that the BiMn grains accumulated on the periphery of the specimen, forming a ring-like MnBi phase-rich layer where MnBi phase aligned along the magnetic direction. This pheromone was analyzed and discussed.     

The onset of steady Bénard-Marangoni convection in a two-layer system of conducting fluid in the presence of a uniform magnetic field

The onset of steady Bénard-Marangoni convection in two horizontal liquid layers of electrically conducting immiscible fluids subjected to a uniform vertical magnetic field and temperature gradient is analysed by means of a combination of analytical and numerical techniques. The free surface can be either deformable or nondeformable and the interface between the fluids is always assumed to be flat. The effect of the lower layer on the critical values of Rayleigh, Marangoni and wave numbers for the onset of steady convection is investigated. When the free surface is nondeformable, the critical parameters for the onset of pure Marangoni convection are increased, whereas for the onset of pure Bénard convection they are decreased compared to the single-layer model. The results for a single-layer and for two-layers are qualitatively similar for Bénard-Marangoni convection when the free surface is deformable. All disturbances can be stabilized with sufficiently strong magnetic field when the free surface is nondeformable. If the free surface is allowed to deform and gravity waves are excluded, then the layers are always unstable to disturbances with sufficiently small wave number with magnetic field. Inclusion of gravity waves has a stabilizing effect on certain disturbances of small wave number in the presence of weak or moderate magnetic field.     

Analysis of the magnetic field and studies of the beam dynamics for H− ions in the University of Manitoba cyclotron

Beam orbit dynamics investigations for H⁻ ions in the completely redesigned central region of the University of Manitoba cyclotron were carried out. The methods and the results of these studies are presented along with an analysis of the cyclotron magnetic field that was previously mapped in 1984.     

Three dimensional dendritic morphology and orientation transition induced by high static magnetic field in directionally solidified Al-10 wt.%Zn alloy

Effect of high static magnetic field on the dendritic morphology and growth direction in directionally solidified Al-10 wt.%Zn alloy were studied by three-dimensional (3D) X-ray micro-computed tomography, Electron Back-scattered Diffraction (EBSD) and X-ray Diffraction (XRD). The application of high static axial magnetic field (5T) during directional solidification was found to destabilize the solid/liquid interface and cause the growth direction of dendrite deviate from thermal gradient, leading to irregular solid/liquid interfacial shape and cellular to dendritic morphology transition. The thermoelectric magnetic convection (TEMC) caused by the interaction of thermoelectric effect and magnetic field was supposed to be responsible for the transition. In addition, the EBSD and XRD results confirm that the preferred growth direction of α-Al was found to transform from the traditionally expected <100> to <110>. The dendrite orientation transition (DOT) in Al-10 wt.%Zn alloy can be attributed to the effect of applied magnetic field on the anisotropy of crystal during solidification. The result indicates the potential application of high static magnetic field in altering the morphology and preferred growth direction of dendrite during directional solidification.     

Effect of weak magnetic field changes on the sensitivity of ultrapure germanium γ-detectors

Experimental data are presented indicating the effect of small changes of the earth’s magnetic field strength H on the efficiency of ultrapure germanium γ-detectors. With a reduction in H by 0.056 Oe and a simultaneous change in direction by 2.8°, the relative reduction of a planar director efficiency (with a vertical direction of the electric field applied to it) for recording γ-quanta with energy 88.03 keV is 0.00028 ± 0.00013. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 62–64, June, 2008.     

Bichromatic state-insensitive trapping of cold 133Cs–87Rb atomic mixtures

We investigate simultaneous state-insensitive trapping of a mixture of two different atomic species, Caesium and Rubidium. The magic wavelengths of the Caesium and Rubidium atoms are different, 935.6 and 789.9 nm respectively, thus single-frequency simultaneous state-insensitive trapping is not possible. We thus identify bichromatic trapping as a viable approach to tune the two magic wavelengths to a common value. Correspondingly, we present several common magic wavelength combinations appropriate for simultaneous state-insensitive trapping of the two atomic species.