Cascade-fluorescence spectroscopy on impact-excited He-atoms using level-crossing techniques

He atoms have been excited by 35 keV-Ne⁺ ions, and magnetic depolarization signals of the induced fluorescent light at 667.8nm (1s3d ¹ D-1s 2p ¹ P) have been investigated. By applying suitable electric fields in addition to the variable magnetic field, the complicated superposition structure of the depolarization signal resulting from cascade processes could be analyzed. Beside direct excitation of 1s 3d ¹ D (53%), cascade excitation through 1s4f (26%), 1s 5g (12%), and 1s5f-levels (6%) contributes significantly to the magnetic depolarization signal. From the signal widths the radiative lifetimes of the 1s4f-levels and 1s5g-levels have been deduced: τ(1s4f)=(74±3)ns, τ(1s5g)=(230±20)ns.     

Quantum-dot size dependence of exciton fine-structure splitting

A systematic variation of the exciton fine-structure splitting with quantum dot size in single MOCVD-grown self-organized InAs/GaAs quantum dots is observed, ranging from several tens to as much as , thus covering more than one order of magnitude. Piezoelectricity is identified to be the dominant factor governing the observed trend. A change in sign of the fine-structure splitting is reported for the first time, originating from quantum dots with confinement potentials elongated in the and crystal direction, respectively.     

用多粒子态进行量子信息分配

我们提出一个用五粒子态将量子信息分裂成几部分的方案。在这个过程中,如果且只有接受者相互合作才能重建初始比特的态。我们所用的量子通道是Bell太和三比特GHZ态的组合态,这些态在实验上都是很容易制备的。这个方案对某些窃听攻击来说是安全的。而且,它还可以用来实现控制的量子隐形传态。     

用多粒子态进行量子信息分配

我们提出一个用五粒子态将量子信息分裂成几部分的方案.在这个过程中,如果有且只有接受者相互合作才能重建初始比特的态.我们所用的量子通道是Bell态和三比特GHZ态的组合态,这些态在实验上都是很容易制备的.这个方案对某些窃听攻击来说是安全的.而且,它还可以用来实现控制的量子隐形传态.     

On the fine-structure splitting in\bar p atoms

Recent measurements of fine-structure splitting in \(\bar p\) atoms of¹⁷⁴Yb are analysed. Effects of nuclear deformation are calculated. The strength of nuclear spin-orbit coupling is determined and its implications on theN \(\bar N\) potential are discussed.     

Hyperfine level-crossing spectroscopy of NH2 with dye-laser excitation

Hyperfine structure of a number of levels of the (0, 9, 0) and (0, 10, 0) vibrational states of the à ²A₁ state of NH₂ has been measured using the technique of magnetic level-crossing. A CW dye-laser served as an excitation source. The resolution achieved is ～ 3 MHz. The analyses have been aided by calculations of the relative fields for the level-crossings in terms of the parameters of a model hamiltonian, together with their relative intensities for linear and non-linear excitation. These calculations are presented for I = ½ and 1 for J = 1 ½, 2 ½, 3 ½, and 4 ½.

Hyperfine parameters for the (0, 10, 0) vibrational state are in good agreement with the one set of literature values, obtained using the independent method of intermodulated fluorescence.

We observe an apparent drop of 30 per cent in the Fermi contact parameter between the (0, 10, 0) and (0, 9, 0) levels. However, it is also found that the hyperfine splittings within the (0, 9, 0) state are not completely in accord with the simple model. These observations are briefly discussed in terms of the Renner effect and the s-p hybrid nature of the molecular orbital occupied by the unpaired electron.     

Dynamical study of femtosecond-laser-ablated liquid-aluminum nanoparticles using spatiotemporally resolved x-ray-absorption fine-structure spectroscopy

We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensed liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.     

Photoacoustic X-ray absorption fine-structure spectroscopy of the NiK-edge

The X-ray absorption in a 5 m thick Ni foil for energies from 8.2 keV to 8.8 keV was measured by the photoacoustic method using a gas-microphone-cell. Results are presented for both photoacoustic amplitude and phase as a function of incident photon energy. The absorption fine structure above the NiK-edge is clearly resolved. The data are compared with a simple theory for the signal generation, and discrepancies are explained by discussing the various energy dissipation channels following the X-ray absorption.     

Measurement of the fine structure separation in the 42 D term of lithium by the method of electric field induced level anti-crossing

An electric field is employed to convert lithium 4² D Zeeman level crossings into anti-crossings. The lithium atoms are excited by electron impact. The anti-crossings are detected by the change in polarization of the light emitted in the 4² D-2² P transition. From the corresponding values of the magnetic field, we obtain 400 (10) MHz for the zero field fine structure energy separationE(4² D _5/2)-E(4² D _3/2).     

Measurement of the hyperfine structure splitting for the 4 and 52 P 1/2 states of sodium using radio-frequency spectroscopy

The hyperfine-structure splitting for the 4 and 5² P ^1/2 states of sodium was measured using step-wise laser excitation combined with rf-resonance techniques. The magnetic dipole interaction constants were found to be a(4² P _1/2)=30.4(5) MHz and a(5₂ P _1/2) =13.3(2) MHz. The results are compared with a theoretical calculation, taking polarization effects into account.     

Cancellation of fine-structure splitting in quantum dots by a magnetic field

We demonstrate control of the fine-structure splitting of the exciton emission lines in single InAs quantum dots by the application of an in-plane magnetic field. The composition of the barrier material and the size and symmetry of the quantum dot are found to determine decrease or increase in the linear polarization splitting of the dominant exciton emission lines with increasing magnetic field. This enables the selection of dots for which the splitting can to be tuned to zero, within the resolution of our experiments. General differences in the g-factors and exchange splittings are found for different types of dot.     

Laboratory spectroscopy and the search for variation of the fine-structure constant

Theories unifying gravity with other interactions suggest that fundamental “constants” could (or even should) vary with time and space in an expanding Universe. The value of the fine-structure constant, $\alpha = e^2/\hbar c$ , can be probed over the history of the Universe using quasar absorption systems. On the other hand by comparing atomic clocks over some reasonably long time period (~ years) we can test whether α is currently changing with time on Earth. In this paper we discuss the some of the directions in which this research is heading and some laboratory measurements of absolute frequency and isotope shift which are much needed for these studies of α-variation. Researchers who are interested in performing these measurements should contact the authors directly.     

Quantum information splitting of a two-qubit Bell state using a four-qubit entangled state

A scheme is proposed for quantum information splitting of a two-qubit Bell state by using a four-qubit entangled state as a quantum channel. In the scenario, it is supposed that there are three legitimate parties, say Alice, Bob and Charlie. Alice is the sender of quantum information. Bob and Charlie are two agents. Alice first performs GHZ state measurement and tells Bob and Charlie the measurement results via a classical channel. It is impossible for Bob to reconstruct the original state with local operations unless help is obtained from Charlie. If Charlie allows Bob to reconstruct the original state information, he needs to perform a single-qubit measurement and tell Bob the measurement result. Using the measurement results from Alice and Charlie, Bob can reconstruct the original state. We also consider the problem of security attacks. This protocol is considered to be secure.     

Determination by quantum beat spectroscopy of fine-structure intervals in a series of highly excited sodium D states

Using the quantum beat method in conjunction with stepwise excitation, we have measured the absolute value of the fine-structure (fs) intervals in a series of highly excited sodium nD states (n=9 to 16). Preliminary Stark effect measurements of these levels also indicate that the fs is inverted. Our results and those previously obtained on the lowest D intervals (n=3 to 6) agree with an empirical formula giving the fs constant as an expansion in odd powers of n^?1. This formula allows the prediction of the as yet not measured 7D and 8D intervals.     

Some remarks on the application of the terms level-crossing and line-crossing in atomic spectroscopy

The differences between level-crossing in light emission, level- and line-crossing in forward scattering and selective reflection as well as in absorption are discussed.     

Exciton polarization, fine-structure splitting, and the asymmetry of quantum dots under uniaxial stress

We derive a general relation between the fine-structure splitting (FSS) and the exciton polarization angle of self-assembled quantum dots under uniaxial stress. We show that the FSS lower bound under external stress can be predicted by the exciton polarization angle and FSS under zero stress. The critical stress can also be determined by monitoring the change in exciton polarization angle. We confirm the theory by performing atomistic pseudopotential calculations for the InAs/GaAs quantum dots. The work provides deep insight into the dot asymmetry and their optical properties and a useful guide in selecting quantum dots with the smallest FSS, which are crucial in entangled photon source applications.