Effects of phase decoherence on the entanglement of a two-qubit anisotropic Heisenberg XYZ chain with an in-plane magnetic field

We investigate the phase decoherence effects on the entanglement of a two-qubit anisotropic Heisenberg model with a nonuniform magnetic field in the x–z-plane. As a measure of the entanglement, the concurrence of the system is calculated. It is shown that when the magnetic field is along the z-axis, the nonuniform and uniform components of the field have no influence on the entanglement for the cases of and , respectively. But when the magnetic field is not along the z-axis, both the uniform and the nonuniform components of the field will introduce the decoherence effects. It is found that the effects of the Heisenberg chain's anisotropy in the Z-direction on the entanglement are dependent on the direction of the field. Moreover, the larger the initial concurrence is, the higher value it will exhibit during the time evolution of the system for a proper set of the parameters ν, Δ, θ, γ , B and b.     

Continuum variable entangled state generated by an asymmetric beam splitter

For an asymmetric beam-splitter a new kind of entangled state is introduced, we then derive the integration measure with which such states can make up a complete and orthonormal representation in two-mode Fock space. We then show how to use in finding new squeezing operator and new squeezed state, whose generation can relies on the asymmetric beamsplitter.     

Retrodiction for coherent communication with homodyne or heterodyne detection

Previous work on the retrodictive theory of direct detection is extended to cover the homodyne detection of coherent optical signal states and . The retrodictive input state probabilities are obtained by the application of Bayes' theorem to the corresponding predictive distributions, based on the probability operator measure (POM) elements for the homodyne process. Results are derived for the retrodictive information on the complex amplitude of the signal field obtainable from the difference photocount statistics of both 4-port and 8-port balanced homodyne detection schemes. The local oscillator is usually assumed much stronger than the signal but the case of equal strengths in 4-port detection is also considered. The calculated probability distributions and error rates are illustrated numerically for values of signal and local oscillator strengths that extend from the classical to the quantum regimes.     

Atomic squeezing in assembly of two two-level atoms interacting with a single mode coherent radiation

Saito and Ueda [Phys. Rev. A 59, 3959 (1999)] studied atomic and radiation squeezing in interaction of a single mode coherent state of radiation with two excited two-level atoms, using the Jaynes Cummings Hamiltonian. They considered α real and studied squeezing of the Dicke operator S_x using the Kitagawa-Ueda criterion for squeezing and coupling times less than or nearly equal to . We obtain results to all orders in coupling time for atoms, which are initially in (i) fully excited, (ii) superradiant or in (iii) ground states and obtain more general results. We use our recently reported criterion for atomic squeezing, of which the Kitagawa-Ueda criterion is a special case, and obtain a much stronger (nearly 95%) atomic squeezing than that (nearly 1.1%) reported by Saito and Ueda.     

Modular construction of special mixed quantum states

For a homogeneous quantum network of N subsystems with n levels each we consider separable generalized Werner states. A generalized Werner state is defined as a mixture of the totally mixed state and an arbitrary pure state : with a mixture coefficient . For this density operator to be separable, will have an upper bound . Below this bound one should alternatively be able to reproduce by a mixture of entirely separable input-states. For this purpose we introduce a set of modules, each contributing elementary coherence properties with respect to a generalized coherence vector. Based on these there exists a general step-by-step mixing process for any . For being a cat-state it is possible to define an optimal process, which produces states right up to the separability boundary ( ).Received: 3 December 2002, Published online: 29 July 2003PACS: 03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bells inequalities, GHZ states, etc.) - 03.67.-a Quantum information - 03.65.-w Quantum mechanics     

Lifetime vibrational interference during the NO 1s-1π* resonant excitation studied by the NO+(A 1Π → X 1Σ+) fluorescence

Dispersed fluorescence from fragments formed after the de-excitation of the 1s^-1π^* resonances of N^*O and NO^* has been measured in the spectral range of 118–142 nm. This range is dominated by lines of atomic nitrogen and oxygen fragments and by the bands in the NO⁺ ion which result from the participator Auger decay of the 1s^-1π^* resonances. Ab-initio calculations of the transition probabilities between vibrational levels during the reaction NO N^*O ⇒ NO were used to explain the observed intensity dependence for the fluorescence bands on the exciting-photon energy across the resonances and on both v^′ and v^′′ vibrational quantum numbers. The multiplet structure of the 1s^-1π^* resonance and lifetime vibrational interference explain the observed exciting-photon energy dependence of the fluorescence intensity. A strong spin-orbit coupling between singlet and triplet states of NO⁺ is proposed to reduce additional cascade population of the state via radiative transitions from the and states and to explain remaining differences between measured and calculated integral fluorescence intensities.     

Hyperfine structure and isotope shift study in singly ionized lead

Hyperfine structure and isotope shifts in five optical transitions: 424.5 nm ( – ), 537.2 nm ( – ), 554.5 nm ( – ), 560.9 nm ( – ) and 666.0 nm ( – ) of Pb  II have been measured. As a light source the discharge tube was used. The hyperfine structure measurements were performed using metallic isotope ²⁰⁷Pb. For isotope shifts measurements natural lead was used. The high resolution spectral apparatus consisted of a silver coated Fabry-Perot etalon and a grating spectrograph combined with a CCD camera used as a detector. In the analysis of the spectra a computer simulation technique was used. The hyperfine structure observations yielded the splitting constants A for seven levels of Pb II. The isotope shift studies enabled to separate the mass and the field shifts and to determine values of changes of the mean square nuclear charge radii.     

Operator product expansion and quark condensate from lattice QCD in coordinate space

We present a lattice QCD determination of the chiral quark condensate based on a new method. We extract the quark condensate from the operator product expansion of the quark propagator at short euclidean distances, where it represents the leading contribution in the chiral limit. From this study we obtain , in good agreement with determinations of this quantity based on different approaches. The simulation is performed by using the -improved Wilson action at on a volume 32³ × 70 in the quenched approximation.Received: 8 March 2005, Revised: 15 April 2005, Published online: 18 May 2005PACS: 11.15.Ha, 11.30.Rd, 12.38.-t, 12.38.Gc     

On the Modified Korteweg–De Vries Equation

We consider the large time asymptotic behavior of solutions to the Cauchy problem for the modified Korteweg–de Vries equation , with initial data . We assume that the coefficient is real, bounded and slowly varying function, such that , where . We suppose that the initial data are real-valued and small enough, belonging to the weighted Sobolev space . In comparison with the previous paper (Internat. Res. Notices 8 (1999), 395–418), here we exclude the condition that the integral of the initial data u ₀ is zero. We prove the time decay estimates and for all , where . We also find the asymptotics for large time of the solution in the neighborhood of the self-similar solution.     

Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy on cluster size in a large range of has been measured. The experimental results indicate that when the cluster size , the average ion energy Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.     

Decelerated molecular beams for high-resolution spectroscopy

Ultimately, the resolution of any spectroscopic experiment is limited by the interaction time between the particles that are to be examined and the measuring device. The obtainable spectroscopic resolution in a molecular beam experiment can be considerably improved using samples of slow molecules, as produced, for example, in a Stark-decelerator. This is demonstrated here by measuring the inversion tunneling spectrum of using a pulsed molecular beam that has been decelerated to about 52 m/s. Hyperfine resolved inversion transitions in in the state (around 1.43 GHz) are induced in a microwave region, and molecules that have undergone the transition are subsequently detected using a UV-laser based ionization detection scheme. To increase the signal intensity, the decelerated molecular beam is both transversally and longitudinally focused into the laser detection region. The observed spectral width of individual hyperfine transitions in the fully resolved spectrum is about 1 kHz, and the standard deviation of the best fit is 62 Hz.Received: 7 September 2004, Published online: 23 November 2004PACS: 33.15.Pw Fine and hyperfine structure - 33.20.Bx Radio-frequency and microwave spectra - 33.40. + f Multiple resonances - 33.70.Jg Line and band widths, shapes, and shifts - 39.10. + j Atomic and molecular beam sources and techniques     

Hyperfine structure and isotope shifts in near-infrared transitions of atomic nitrogen

We have obtained Doppler-free spectra of transitions in the → 2p²(³P) and → multiplets of atomic nitrogen using saturated absorption spectroscopy. These multiplets consist of respectively of seven and eight transitions, and have center of gravity wavelengths of 821 nm and 869 nm. Values for the hyperfine structure coupling constants of all the upper and lower states for these multiplets were obtained for both ¹⁴N and ¹⁵N. Isotope shifts of three transitions in each multiplet were also measured, and a significant J-dependence to the shifts was observed.     

Soft X-ray contact microscopy of nematode Caenorhabditis elegans

Soft X-ray Contact Microscopy (SXCM) of Caenorhabditis elegans nematodes with typical length m and diameter m has been performed using the PALS laser source of wavelength m and pulse duration ps. Pulsed soft X-rays were generated using molybdenum and gold targets with laser intensities W/cm². Images have been recorded on PMMA photo resists and analyzed using an atomic force microscope operating in contact mode. Cuticle features and several internal organs have been identified in the SXCM images including lateral field, cuticle annuli, pharynx, and hypodermal and neuronal cell nuclei.Received: 18 February 2004, Published online: 29 June 2004PACS: 42.62.Be Biological and medical applications - 07.85.Tt X-ray microscopes - 87.59.Bh X-ray radiographyA color version of the figures is available in electronic form at .     

Electron impact excitation of 2p and 3p states of hydrogen at intermediate energies

The recent theoretical work by Bartlett et al. [J. Phys. B 38, L95 (2005)] and the latest measurements on the reduced Stokes parameters , and for 54.4 eV electron impact excitation of the 2p state atomic hydrogen by Williams and Mikosza [J. Phys. B 39, 4113 (2006)] has motivated the present work. A coupled-channel-optical calculation with 9 and 12 atomic states supplemented with the continuum optical potentials for the stronger coupling channels has been performed. The calculated n = 2 and n = 3 differential cross sections and the reduced Stokes parameters are comparable with the state-of-the art calculations. There is closer agreement between the present calculations and the experimental measurements for the reduced Stokes parameters and in the n = 2p excitation at 54.4 eV. The present CCO calculations also display good accord with the limited experimental data for the reduced Stokes parameters in the n=3p excitation.     

Noise sensitivity of an atomic velocity sensor

We use Bloch oscillations to accelerate coherently rubidium atoms. The variation of the velocity induced by this acceleration is an integer number times the recoil velocity due to the absorption of one photon. The measurement of the velocity variation is achieved using two velocity selective Raman -pulses: the first pulse transfers atoms from the hyperfine state 5S1/2, $" align="middle" border="0"> to 5S1/2, $" align="middle" border="0"> into a narrow velocity class. After the acceleration of this selected atomic slice, we apply the second Raman pulse to bring the resonant atoms back to the initial state 5S1/2, $" align="middle" border="0"> . The populations in (F=1 and F=2) are measured separately by using a one-dimensional time-of-flight technique. To plot the final velocity distribution we repeat this procedure by scanning the Raman beam frequency of the second pulse. This two -pulses system constitutes then a velocity sensor. Any noise in the relative phase shift of the Raman beams induces an error in the measured velocity. In this paper we present a theoretical and an experimental analysis of this velocity sensor, which take into account the phase fluctuations during the Raman pulses.     

Colour reconnection in e+e– → W+W–at {\sqrt s } =180–209 GeV

The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies in the range ≃ 189–209 using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles in hadronic decays of . Measurements of inclusive charged particle multiplicities, and of their angular distribution with respect to the four jet axes of the events, are used to test models of colour reconnection. The data are found to exclude extreme scenarios of the Sj?strand-Khoze Type I () model and are compatible with other models, both with and without colour reconnection effects. In the context of the model, the best agreement with data is obtained for a reconnection probability of 37%. Assuming no colour reconnection, the charged particle multiplicity in hadronically decaying W bosons is measured to be =19.38±0.05(stat.)±0.08(syst.). Arrival of the final proofs: 28 November 2005     

Two-step laser optogalvanic spectroscopy of the odd-parity Rydberg states of atomic mercury

We present new experimental data on the highly excited levels in mercury using the two-step laser excitation and optogalvanic detection technique in conjunction with a RF discharge cell. The 6s7s ³S₁ intermediate level has been accessed from the 6s6p ³P₂ metastable level that is collisionally populated in the mercury discharge in the presence of a buffer gas at a pressure of about 1 Torr. Two beams fromtwo different dye lasers pumped with a common excimer laser were passed through the discharge cell containing mercury vapors. The first laser was tuned to 6s7s ³S₁ level whereas the second laser was scanned covering the wavelength region between 544-458 nm. We have observed the 6snp ³P₀ ( ), 6snp ( ), 6snp ( ) and 6snp ) Rydberg series. The 6snp Rydberg series to such high n-value has been reported for the first time. The first ionization potential of mercury is determined from the 6snp Rydberg series as 84184.15 0.05 cm^-1. Some collisionally induced parity forbidden transitions have also been located that are identified as 6sns ( ) series.Received: 5 November 2003, Published online: 20 January 2004PACS: 31.50.-x Potential energy surfaces - 32.30.Jc Visible and ultraviolet spectra - 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)     

Triple differential cross-sections of Ne (2s<Superscript>2</Superscript>) in coplanar to perpendicular plane geometry

The distorted wave Born approximation (DWBA) with the spin averaged static exchange potential has been used to calculate the triple differential cross-sections (TDCSs) for Ne (2s ²) ionization by electron impact in coplanar to perpendicular plane symmetric geometry at 110.5 eV incident electron energy. The present theoretical results at gun angles (coplanar symmetric geometry) and (perpendicular plane geometry) are in satisfactory agreement with the available experimental data. A deep interference minimum appears in the TDCS in the coplanar symmetric geometry and a strong peak at scattering angle caused by the single collision mechanism has been observed in the perpendicular plane geometry. The TDCSs at the gun angles , and are predicted.Received: 16 July 2002, Published online: 22 July 2003PACS: 34.80.Gs Molecular excitation and ionization by electron impact - 34.80.Dp Atomic excitation and ionization by electron impact     

Metastable level lifetimes from electron-shelving measurements with ion clouds and single ions

The lifetime of the -level in singly-ionized calcium has been measured by the electron-shelving technique on different samples of rf trapped ions. The metastable state has been directly populated by exciting the dipole-forbidden transition. In ion clouds, the natural lifetime of this metastable level has been measured to be ( ) ms. For the single-ion case, we determined a lifetime of ( ) ms. The -error bars at the 2%-level have different origins for the two kinds of experiments: data fitting methods for lifetime measurements in an ion cloud and control of experimental parameters for a single ion. De-shelving effects are extensively discussed. The influence of differing approaches for the processing of the single-ion quantum jump data on the lifetime values is shown. Comparison with recent measurements shows excellent agreement when evaluated from a given method.Received: 14 November 2003, Published online: 24 February 2004PACS: 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Pj Optical cooling of atoms, trapping