Non-Abelian Berry's phase effects and optical pumping of atoms

We predict experimentally verifiable manifestations of non-Abelian Berry's phase effects for atoms in external collinear electric and magnetic fields. The field strengths are arranged so as to cause accidental degeneracy between atomic states. The relevant theoretical results, which have been presented in detail elsewhere, are summarized and explained. We propose an experiment using optically pumped metastable multiplets of Pb²⁰⁸ in an atomic beam apparatus to test these predictions. We estimate required experimental parameters, and conclude that the proposed experiment can realistically be performed.     

Towards the nuclear matter-quark matter phase transition

Baryon magnetic moments are considered in the quark model. Small contributions to the moments are assumed to arise from configuration mixing (including configurations with orbital angular momentum) in the baryon wave functions, from SU (3) breaking, and from the dependence of the effective quark masses on their environment. It is found that these contributions can improve the agreement of the quark model with experiment. However, so long as quarks have Dirac magnetic moments, charge symmetry holds, and SU (3) breaking effects are small, there is a residual disagreement between predictions of the model and values of some of the recently measured hyperon magnetic moments.     

Four-pulse interferometric recordings of transient events by pulsed TV holography

With traditional double-pulsed holographic interferometry or pulsed TV holography, the experiment usually has to be repeated to allow the recording of a time sequence of interferograms of the event. With the proposed technique a sequence of four interferograms of a solitary transient event is measured. A twin oscillator, injection-seeded, pulsed Nd:YAG laser is incorporated into a pulsed TV holography set-up. With orthogonal polarisation and double pulsing of each of the two channels of the laser, four pulses are recorded on two separate CCD-frames. Four interferograms of a laser-impacted plate obtained from the same experiment, show how the bending waves develop and propagate in the plate.     

Quantum path interferences in high-order harmonic generation

We have investigated the intensity dependence of high-order harmonic generation in argon when the two shortest quantum paths contribute to the harmonic emission. For the first time to our knowledge, experimental conditions were found to clearly observe interference between these two quantum paths that are in excellent agreement with theoretical predictions. This result is a first step towards the direct experimental characterization of the full single-atom dipole moment and demonstrates an unprecedented accuracy of quantum path control on an attosecond time scale.     

Angle-resolved elastic peak electron spectroscopy: Role of surface excitations

We analyze the possibility of determining the surface excitation parameter (SEP) from the dependence of the elastic backscattering signal intensity on the emission angle. It has been found that the shape of this dependence is reasonably well described by the theoretical model implemented in a typical Monte Carlo simulation strategy. As shown recently, the mean percentage deviation between the experimental angular dependence and the theoretical dependence is equal to 8.82% at 200 eV, 6.28% at 500 eV and 4.69% at 1000 eV. In the theoretical model used, the surface energy losses were ignored. Close inspection of the deviations between theory and experiments indicates systematic trends that can be ascribed to the surface energy losses. We found here that taking into the account the surface energy losses further improves the agreement between theory and experiment. The total mean percentage deviation, equal to 6.65%, decreases to 5.59% if the mathematical form of the Chen formula for SEP is used, or to 5.16% if the Oswald expression is used. The material dependent coefficients in the expression of SEP derived from the emission angle dependence of the elastic peak intensity differ from these coefficients resulting from other methods. We conclude that the determination of SEP from shape of the angular dependence requires the experimental data of high quality, and the reliable theoretical model describing elastic electron backscattering.     

Acousto-optic lens for pulsed lasers

Theoretical predictions of the acousto-optic interaction under Raman-Nath conditions of ultrasound and laser light with a beam width w comparable to or smaller than the ultrasonic wavelength lambda are experimentally investigated, and good agreement between experiment and prediction is found. The experimental setup consists of a pulsed laser, emitting pulses that are synchronized with the sound frequency by means of a controllable delay time. When w approximately lambda, strong focusing is obtained for most delay times. The lensing properties of this configuration are carefully investigated.     

Functional polyethylene glycol derivatives nanostructured thin films synthesized by matrix-assisted pulsed laser evaporation

We report the thin film deposition by matrix-assisted pulsed laser evaporation (MAPLE) of a polymer conjugate with an hydrophilic sequence between metronidazole molecules that was covalently attached to both oligomer ends of carboxylate poly(ethylene glycol) (PEG 1.5-metronidazole). A pulsed KrF* excimer laser was used to deposit the drug-polymer composite films. Fourier transform infrared spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical properties similar to the starting materials. The dependence of the surface morphology on incident laser fluence is given.     

共线双脉冲激光诱导击穿光谱技术检测铝合金中的Cr和Mn

采用两台波长1064 nm的调Q脉冲Nd ∶YAG激光器和多通道小型光纤光栅光谱仪,建立了一套共线双脉冲激光诱导击穿光谱分析装置。与单脉冲激光诱导技术相比,在最佳双脉冲时间延时8 μs时,Mn I 403.07 nm和Cr I 425.43 nm的光谱强度分别增加了14.3倍和17.2倍,以这两条谱线为分析线,铝合金中Mn和Cr的检测限分别由单脉冲时的73和94.5 μg/g降低至双脉冲时的3.76和4.26 μg/g,检测灵敏度提高了约20倍。     

Observation of restricted diffusion in the presence of a free diffusion compartment: Single- and double-PFG experiments

Theoretical and experimental studies of restricted diffusion have been conducted for decades using single pulsed field gradient (s-PFG) diffusion experiments. In homogenous samples, the diffusion–diffraction phenomenon arising from a single population of diffusing species has been observed experimentally and predicted theoretically. In this study, we introduce a composite bi-compartmental model which superposes restricted diffusion in microcapillaries with free diffusion in an unconfined compartment, leading to fast and slow diffusing components in the NMR signal decay. Although simplified (no exchange), the superposed diffusion modes in this model may exhibit features seen in more complex porous materials and biological tissues. We find that at low q-values the freely diffusing component masks the restricted diffusion component, and that prolongation of the diffusion time shifts the transition from free to restricted profiles to lower q-values. The effect of increasing the volume fraction of freely diffusing water was also studied; we find that the transition in the signal decay from the free mode to the restricted mode occurs at higher q-values when the volume fraction of the freely diffusing water is increased. These findings were then applied to a phantom consisting of crossing fibers, which demonstrated the same qualitative trends in the signal decay. The angular d-PGSE experiment, which has been recently shown to be able to measure small compartmental dimensions even at low q-values, revealed that microscopic anisotropy is lost at low q-values where the fast diffusing component is prominent. Our findings may be of importance in studying realistic systems which exhibit compartmentation.     

Boundary conditions of the RGE flow in the noncommutative geometry approach to particle physics and cosmology

We investigate the effect of varying boundary conditions on the renormalization group flow in a recently developed noncommutative geometry model of particle physics and cosmology. We first show that there is a sensitive dependence on the initial conditions at unification, so that, varying a parameter even slightly can be shown to have drastic effects on the running of the model parameters. We compare the running in the case of the default and the maximal mixing conditions at unification. We then exhibit explicitly a particular choice of initial conditions at the unification scale, in the form of modified maximal mixing conditions, which have the property that they satisfy all the geometric constraints imposed by the noncommutative geometry of the model at unification, and at the same time, after running them down to lower energies with the renormalization group flow, they still agree in order of magnitude with the predictions at the electroweak scale.     

Parametric polariton amplification in semiconductor microcavities

We present novel experimental results demonstrating the coherence properties of the nonlinear emission from semiconductor microcavities in the strong coupling regime, recently interpreted by parametric polariton four-wave mixing. We use a geometry corresponding to degenerate four-wave mixing. In addition to the predicted threshold dependence of the emission on the pump power and spectral blueshift, we observe a phase dependence of the amplification which is a signature of a coherent polariton wave mixing process.     

Uniqueness of the QCD corrections to the Drell-Yan and Deep Inelastic Scattering processes

We present a complete calculation of one loop QCD corrections to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes under various infrared and collinear singularity regularization schemes. We use our final results which have surprisingly simple forms in an analysis of the scheme dependence problem for these singularities. We also comment on some of the other proposals made recently for the resolution of the same problem.     

超冷nS Rydberg原子的态转移

本文从实验上研究了超冷nS Rydberg原子在外电场脉冲作用下的态转移现象. 采用双光子激发超冷基态原子制备超冷Rydberg原子, 通过脉冲场电离法探测超冷Rydberg原子的离子信号, 实验研究了由外加脉冲电场产生的nS能级和多重态的避免交叉, 获得了在外电场脉冲作用下nS态原子的态转移现象, 实验与理论计算的结果相一致. 关键词： Rydberg原子 态转移 能级避免交叉     

High-frequency 180 GHz PELDOR

For aromatic organic radicals, pulsed electron-electron double resonance (PELDOR) experiments at high magnetic fields offer the possibility to achieve orientation-selective pumping and detection that could allow one not only to determine the distance between paramagnetic species but also their relative orientation with respect to the interconnecting dipolar axis. We present a PELDOR two-frequency setup that was introduced into our homebuilt 180 GHz pulsed electron paramagnetic resonance (EPR) spectrometer and we discuss its technical and experimental features. The capability of 180 GHz PELDOR has been tested using the three-pulse ELDOR sequence on the protein RNR-R2 (ribonucleotide reductase) fromEscherichia coli, which contains two tyrosyl radicals at a distance of 3.3 nm. At 180 GHz, orientation selectivity is observed and the modulation frequency was found in good agreement with theoretical predictions, which take into account the relative orientation of the radicals from X-ray data.     

Bell Locality and the Nonlocal Character of Nature

It is demonstrated that hidden variables of a certain type follow logically from a certain local causality requirement (“Bell Locality”) and the empirically well-supported predictions of quantum theory for the standard EPR-Bell set up. The demonstrated hidden variables are precisely those needed for the derivation of the Bell Inequalities. We thus refute the widespread view that empirical violations of Bell Inequalities leave open a choice of whether to reject (i) locality or (ii) hidden variables. Both principles are indeed assumed in the derivation of the inequalities, but since, as we demonstrate here, (ii) actually follows from (i), there is no choice but to blame the violation of Bell's Inequality on (i). Our main conclusion is thus no Bell Local theory can be consistent with what is known from experiment about the correlations exhibited by separated particles. Aside from our conclusion being based on a different sense of locality this conclusion resembles one that has been advocated recently by H.P. Stapp. We therefore also carefully contrast the argument presented here to that proposed by Stapp.     

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (F(p/r) and G(p/r)), magic pulsed field gradient (MPFG) ratios for the prepare (G(p)/F(p)) and the read (G(r)/F(r)) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the tau-intervals between the pi and pi/2 rf pulses, these two MPFG ratios coincide to eta=G(p/r)/F(p/r)=1-8/[1+(1/3)(delta/tau)(2)]. Since the width of the pulsed field gradients (delta) is bounded by 0< or =delta< or =tau, eta can only be in the range of 5< or =-eta< or =7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.     

NMR relaxation and pulsed field gradient study of alginate bead porous media

Experiments are presented, which correlate molecular displacement with the multi-exponential T2 relaxation times of water flowing and diffusing through an alginate bead pack. Three systems were studied comprising beads of 3, 1 or < mm in diameter. T2-resolved propagators were obtained through a combined pulsed gradient stimulated echo (PGSTE) and Carr-Purcell-Meiboom-Gill (CPMG) experiment. Fourier transformation with respect to q produces a propagator for each echo in the CPMG train. Inverse Laplace transformation of the CPMG decays for each point (Z) in the propagator produced a two-dimensional propagator. Analysis of these two-dimensional propagators provided insight into the transport and exchange behaviour of water flowing through this system. This experiment has been simulated in a model bead structure and the resulting T2 relaxation time behaviour and T2-resolved propagators were found to be in good agreement with the experimental data. We also present a theoretical analysis of the response to the combined PGSTE/CPMG sequence in the simple model case of Pouseille flow in a cylindrical capillary, where diffusion to a surface sink is assumed to be the dominant relaxation mechanism.     

Slow light via four-wave mixing in a hot rubidium vapour

In this work,we report on an off-resonant four-wave mixing experiment via a ladder-type configuration in a hot rubidium atomic vapour.We find for the first time,to the best of our knowledge,that the generated light is delayed compared with the reference.At the same time,the seeded signal beam is also delayed,though the delay time is not as so large as the one that the generated light has.Both delayed times can be adjusted experimentally by controlling the two-photon detuning.The experimental results are in good agreement with our theoretical predictions.Our results may be important for storing telecom-band photons.