Jonathan G. Underwood

Time‐Resolved Photoelectron Spectroscopy of Nonadiabatic Dynamics in Polyatomic Molecules

This review article discusses advances in the use of time-resolved photoelectron spectroscopy for the study of non-adiabatic processes in molecules. A theoretical treatment of the experiments is presented together with a number of experimental examples.

Methods and applications of femtosecond time-resolved photoelectron spectroscopy

Femtosecond time-resolved photoelectron spectroscopy is emerging as a new technique for investigating polyatomic excited state dynamics. Due to the sensitivity of photoelectron spectroscopy to both electronic configurations and vibrational dynamics, it is well suited to the study of ultrafast non-adiabatic processes such as internal conversion, often occurring on sub-picosecond time scales. We discuss technical requirements for such experiments, including laser systems, energy and angle resolved photoelectron spectrometers and new detectors for coincidence experiments. We illustrate these methods with examples from diatomic wavepacket dynamics and ultrafast non-adiabatic processes in polyatomic molecules.

High harmonic emission from a superposition of multiple unrelated frequency fields

We report observations and analysis of high harmonic generation driven by a superposition of fields at 1290 nm and 780 nm. These fields are not commensurate in frequency and the superposition leads to an increase in the yield of the mid-plateau harmonics of more than two orders of magnitude compared to using the 1290 nm field alone. Significant extension of the cut-off photon energy is seen even by adding only a small amount of the 780 nm field. These observations are explained by calculations performed in the strong field approximation. Most importantly we find that enhancement is found to arise as a consequence of both increased ionization in the sum-field and modification of the electron trajectories leading to an earlier return time. The enhanced yield even when using modest intensity fields of 5 x 10(13) Wcm(-2) is extended to the 80 eV range and is a promising route to provide a greater photon number for applications in XUV imaging and time-resolved experiments at a high repetition rate.

Two-photon state selection and angular momentum polarization probed by velocity map imaging: Application to H atom photofragment angular distributions from the photodissociation of two-photon state selected HCl and HBr

A formalism for calculating the angular momentum polarization of an atom or a molecule following two-photon excitation of a J-selected state is presented. This formalism is used to interpret the H atom photofragment angular distributions from single-photon dissociation of two-photon rovibronically state selected HCl and HBr prepared via a Q-branch transition. By comparison of the angular distributions measured using the velocity map imaging technique with the theoretical model it is shown that single-photon dissociation of two-photon prepared states can be used for pathway identification, allowing for the identification of the virtual state symmetry in the two-photon absorption and/or the symmetry of the dissociative state. It is also shown that under conditions of excitation with circularly polarized light, or for excitation via non-Q-branch transitions with linearly polarized light the angular momentum polarization is independent of the dynamics of the two-photon transition and analytically computable.

Measurement of electronic structure from high harmonic generation in non-adiabatically aligned polyatomic molecules

We have explored the use of laser driven high-order harmonic generation to probe the electronic structure and symmetry of conjugated polyatomic molecular systems. We have investigated non-adiabatically aligned samples of linear symmetric top, nonlinear symmetric top and asymmetric top molecules, and we have observed signatures of their highest occupied molecular orbitals in the dependence of harmonic yields on the angle between the molecular axis and the polarization of the driving field. A good quantitative agreement between the measured orientation dependence of high harmonic generation and calculations employing the strong field approximation has been found. These measurements support the extension of molecular imaging techniques to larger systems.

Stable kilohertz rate molecular beam laser ablation sources

We describe a stable kHz rate laser ablation/desorption supersonic molecular beam source for use in kHz rate laser experiments. With the development of modern lasers that typically operate at kHz rates, a need has arisen for stable molecular beam laser ablation/desorption sources for the study of involatile species. Many biomolecules of interest cannot be brought into the gas phase without thermal decomposition by simply heating the substrate and most (especially refractory) metals have melting and boiling points that are impossible to reach with conventional ovens. The source is based upon strong nonresonant interaction of a dithering laser focus with a rotating and translating solid rod, hydrodynamic transport of the ablated/desorbed material in helium or argon, and subsequent supersonic expansion. Further design details include flexible and easy adjustment of the source for rapid prototyping and optimization for kHz rate performance. Due to the high rate of sample removal, a major concern is clogging of the nozzle and laser input channel due to both material condensation and debris formation. In order to illustrate the range of applications, we demonstrate (1) the kHz laser ablation of a high temperature refractory metal (niobium) for use in studies of metal clusters; and (2) the kHz laser desorption and jet cooling of an involatile biomolecule (the DNA base guanine) for use in spectroscopic and dynamical studies. This kHz source design has been shown to be stable for over 12 continuous hours of operation (>4×10 7 laser shots) and can be readily scaled to even higher repetition rates (>10 kHz).

Enhancement of high harmonics generated by field steering of electrons in a two-color orthogonally polarized laser field

We demonstrate enhancement by 1 order of magnitude of the high-order harmonics generated in argon by combining a fundamental field at 1300 nm (10(14) W cm(-2)) and its orthogonally polarized second harmonic at 650 nm (2 × 10(13) W cm(-2)) and by controlling the relative phase between them. This extends earlier work by ensuring that the main effect is the combined field steering the electron trajectory with negligible contribution from multiphoton effects compared to the previous schemes with 800/400 nm fields. We access a broad energy range of harmonics (from 20 eV to 80 eV) at a low laser intensity (far below the ionization saturation limit) and observe deep modulation of the harmonic yield with a period of π in the relative phase. Strong field theoretical analysis reveals that this is principally due to the steering of the recolliding electron wave packet by the two-color field. Our modeling also shows that the atto chirp can be controlled, leading to production of shorter pulses.

Ultrafast science and development at the Artemis facility

The Artemis facility for ultrafast XUV science is constructed around a high average power carrier-envelope phasestabilised system, which is used to generate tuneable pulses across a wavelength range spanning the UV to the far infrared, few-cycle pulses at 800nm and short pulses of XUV radiation produced through high harmonic generation. The XUV pulses can be delivered to interaction stations for materials science and atomic and molecular physics and chemistry through two vacuum beamlines for broadband XUV or narrow-band tuneable XUV pulses. The novel XUV monochromator provides bandwidth selection and tunability while preserving the pulse duration to within 10 fs. Measurements of the XUV pulse duration using an XUV-pump IR-probe technique demonstrate that the XUV pulselength is below 30 fs for a 28 fs drive laser pulse. The materials science station, which contains a hemispherical electron analyser and five-axis manipulator cooled to 14K, is optimised for photoemission experiments with the XUV. The end-station for atomic and molecular physics and chemistry includes a velocity-map imaging detector and molecular beam source for gas-phase experiments. The facility is now fully operational and open to UK and European users for twenty weeks per year. Some of the key new scientific results obtained on the facility include: the extension of HHG imaging spectroscopy to the mid-infrared; a technique for enhancing the conversion efficiency of the XUV by combining two laser fields with non-harmonically related wavelengths; and observation of D3+ photodissociation in intense laser fields.

Quantum control via the dynamic Stark effect: Application to switched rotational wave packets and molecular axis alignment

We study the influence of delayed optical feedback from a short external cavity (EC) on the emission dynamics of vertical-cavity surface-emitting semiconductor lasers (VCSELs). We find the emergence of pulse packages (PP) exhibiting characteristics which originate from the interplay of time-delay induced dynamics and polarization mode (PM) competition. We provide detailed analysis of the polarization dynamics applying complementary cross-correlation and spectral analysis techniques. The analysis reveals an interplay of the dynamics linked to the hierarchy of time scales present in the laser system: the fast time scale of the EC delay, the slower time scale of the PP, and the slow time scale of the polarization mode competition. For an analysis of the dynamics we provide a toolbox of methods adapted to the different relevant time scales and temporal variations of the dynamics. This complementary view unveils distinct changes in the relative oscillation phase of the two PM for increasing the injection current on both the fast and the slow time scales. Our results emphasize the significance of the polarization mode competition for PP dynamics in VCSELs, contrasting the observed behavior to what was reported for edge emitters.We present the results of a set of quantum and semiclassical simulations of the response of H{sub 2}{sup +} molecular ions, when submitted to a strong and ultrashort (femtosecond) infrared laser pulse. Going beyond the framework of the fixed nuclei (Born-Oppenheimer) approximation, we have addressed several questions related to the competition between excitation, dissociation, and ionization. In this context, it is shown that semiclassical simulations can provide valuable informations about the dynamics of the processes considered.By a comparative analysis of the emission of highly charged ions and energetic electrons the interaction dynamics of intense femtosecond laser fields (10{sup 13}-10{sup 14} W/cm{sup 2}) with nanometer-sized silver clusters is investigated. Using dual laser pulses with variable optical delay the time-dependent cluster response is resolved. A dramatic increase both in the atomic charge state of the ions and the maximum electron kinetic energy is observed for a certain delay of the pulses. Corresponding Vlasov calculations on a metal cluster model system indicate that enhanced cluster ionization as well as the generation of fast electrons coincide with resonant plasmon excitation.A study is made of low-energy electron-impact single ionization of ground-state helium. The time-dependent close-coupling method is used to calculate total integral, single differential, double differential, and triple differential ionization cross sections for impact electron energies ranging from 32 to 45 eV. For all quantities, the calculated cross sections are found to be in very good agreement with experiment, and for the triple differential cross sections, good agreement is also found with calculations made using the convergent close-coupling technique.The ionization of xenon Rydberg atoms excited to the lowest states in the n=17 and n=20 Stark manifolds at a flat Au(111) surface is investigated. Despite the strong perturbations in the energies and structure of the atomic states that occur as the surface is approached, it is shown that, under appropriate conditions, each incident atom can be detected as an ion and that the experimental data can be well fit by assuming that the ionization rate on average increases exponentially as the surface is approached. The ionization rates are compared to theoretical predictions.Electron-impact ionization cross sections for H{sub 2} are calculated using a nonperturbative time-dependent close-coupling method. In a standard frozen-core approximation, the six-dimensional wave function for the valence target electron and the incident projectile electron is expanded in products of rotational functions. The time-dependent Schroedinger equation for the two-electron system is then reduced to a set of close-coupled partial differential equations for the four-dimensional expansion functions in (r{sub 1},{theta}{sub 1},r{sub 2},{theta}{sub 2}) center-of-mass spherical polar coordinates. The nonperturbative close-coupling results are found to be over a factor of 2 lower than perturbative distorted-wave results, but in excellent agreement with experimental measurements, at incident electron energies near the peak of the total integrated cross section.The high precision relativistic and radiative corrections to the energy of the excited 3 {sup 1}S state of the beryllium atom are obtained. The nonrelativistic wave function, expanded in a basis of exponentially correlated Gaussian functions, yields the lowest upper bounds to the energy of 2 {sup 1}S and 3 {sup 1}S states. By means of the integral representation, a reference-quality Bethe logarithm has been obtained. The resulting theoretical 2 {sup 1}S-3 {sup 1}S transition energy amounts to 54 677.78(45) cm{sup -1} and differs from the known experimental value by about 0.5 cm{sup -1}.Nonlinear optical quantum gates can be created probabilistically using only single-photon sources, linear optical elements, and photon-number-resolving detectors. These gates are heralded but operate with probabilities much less than 1. There is currently a large gap between the performance of the known circuits and the established upper bounds on their success probabilities. One possibility for increasing the probability of success of such gates is feed-forward, where one attempts to correct certain failure events that occurred in the gates operation. In this Brief Report we examine the role of feed-forward in improving the success probability. In particular, for the nonlinear sign-shift gate, we find that in a three-mode implementation with a single round of feed-forward the optimal average probability of success is approximately given by p{sub success}=0.272. This value is only slightly larger than the general optimal success probability without feed-forward, p{sub success}=0.25.We investigate the relation between the thermalization cross section {sub T} and the scattering length a of spin-polarized metastable neon (Ne{sup *}) in the Doppler-limited temperature regime. We show that a temperature-dependent, quantum-mechanical, five-channel calculation allows one to obtain a consistent with the mass scaling rule between {sup 20}Ne{sup *} and {sup 22}Ne{sup *} from recent data of {sub T} by Spoden et al. [Phys. Rev. Lett. 94, 223201 (2005)]. We find a=+24{sub -5}{sup +5}a{sub 0} or a=-128{sub -22}{sup +16}a{sub 0} for {sup 20}Ne{sup *} and +115 < or approx. a < or approx. +160a{sub 0} for {sup 22}Ne{sup *}, respectively. According to numerical simulations of the evaporative cooling process, these values of a are not large enough to make Bose-Einstein condensation of Ne{sup *} feasible for realistic experimental conditions, given the measured ionization rate constants.We report a new measurement of the photoionization cross section for the (2p){sup 5}(3p) {sup 3}D{sub 3} state of neon at the wavelengths of 351 and 364 nm. These data were obtained by monitoring the decay of the fluorescence of atoms trapped in a magneto-optical atom trap under the presence of a photoionizing laser, a technique developed by Dinneen et al. [Opt. Lett. 17, 1706 (1992)]. We obtain absolute photoionization cross sections of 2.05{+-}0.25x10{sup -18} cm{sup 2} at {lambda}=351 nm and 2.15{+-}0.25x10{sup -18} cm{sup 2} at {lambda}=364 nm, an improvement in accuracy of a factor of 4 over previously published values. These new values are not consistent with published theoretical data.We present a theoretical investigation on the open-aperture Gaussian-beam Z-scan technique for two dominant saturable absorption models, by using the Adomian decomposition method. Analytic expressions of the Z-scan traces are deduced for a cw laser and a pulsed laser, respectively; in particular, for performable simulations, the optimal sum upper limit is found. We give an experimental demonstration, in which a side-chain azobenzene polymer poly [6-[1-(4-(4-nitrophenylazo)phenyl) piperazine] hexyl methacrylate] (Pda) film behaves as a test sample. The results manifest that our theory is reasonable and the Pda film is a good saturable absorber at the wavelength of 532 nm.The time-dependent Schroedinger equation is solved numerically to investigate laser-assisted charge transfer in He{sup 2+}+H+nh{nu} collisions at 1 keV in the semiclassical impact parameter approach. Laser polarizations parallel and perpendicular to the projectile trajectory are studied. For both polarizations even a moderately intense laser (I{sub 0}=3.5x10{sup 12} W/cm{sup 2}) significantly increases the reaction probability. In addition, we find that the relative collision-laser phase has little influence on the charge transfer. We focus on parameters more favorable to experiment.We describe a quantum algorithm to prepare an arbitrary pure state of a register of a quantum computer with fidelity arbitrarily close to 1. Our algorithm is based on Grovers quantum search algorithm. For sequences of states with suitably bounded amplitudes, the algorithm requires resources that are polynomial in the number of qubits. Such sequences of states occur naturally in the problem of encoding a classical probability distribution in a quantum register.The {sup 1,3}P{sup o} resonance states of positronium negative ions embedded in dense plasma environments are determined by calculating the density of resonance states using the stabilization method. A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charge particles, together with employing highly correlated wave functions to represent the correlation effect between them. We have calculated one {sup 1}P{sup o} and two {sup 3}P{sup o} resonances associated with and below the n=2 threshold of the positronium atom. The resonance energies and widths for various Debye lengths ranging from infinity to a small value are reported.The phenomenon of Coulomb explosion is studied through qualitative numerical simulations of clusters irradiated with intense ultrashort laser pulses. We introduce a semiquantum approach which allows us to model two different types of materials--akin to rare gases and dielectrics--and which is appropriate for both low- and high-energy domains, i.e., the thermodynamic regime and the Coulomb explosion regime. Through a detailed study of clusters submitted to laser pulses of various intensities, we demonstrate that Coulomb explosion is the process responsible for cluster explosion under femtosecond laser pulses. We examine the differences in the dynamics of explosion of rare-gas clusters as a function of the wavelength of the incident laser radiation. For dielectric clusters, our simulations reveal a fragmented explosion mechanism; the influence of the size of the cluster is also studied.We propose a scheme for squeezing vibrational wave packets in the ground (or excited) states of diatomic molecules that uses pulse sequences of strong nonresonant short pulses. The physical mechanism of the scheme is a two step process involving adiabatic and diabatic transformations of the wave packet. The first step is the adiabatic stretching of the wave packet on a light-induced potential, and the second step is dynamic squeezing by free evolution after ultrashort (i.e., diabatic) population transfer. We show that this sequence of transformations can be performed very efficiently with a simple two pulse sequence with slow switch on and fast switch off pulse shapes, and we analyze the required physical resources that are needed. We test the scheme on a model of harmonic oscillators and on the Rb{sub 2} dimer. Finally, different possible generalizations are proposed.We show that the Comment by Diener and Ho [Phys. Rev. A 73, 017601 (2006)] is based on the misunderstanding that the Hamiltonian used by Dickerscheid et al. to describe Feshbach resonances in an optical lattice is a microscopic Hamiltonian as opposed to an effective Hamiltonian.We study nonclassical polarization states characterized by polarization distributions taking negative values. We consider two different families of polarization distributions that include polarization analogs of the Wigner function. We apply different measures of nonclassical behavior such as the nonclassical depth and the distance of the polarization distribution to its modulus. This approach is applied to relevant quantum field states such as one-photon states, SU(2) coherent states, quadrature coherent states, and twin number states. We examine observables allowing the detection of the negativity of the polarization distributions.Carbon and oxygen dimers with charge states 1+ and 3+ were implanted into GaAs along the [100] direction at an energy of 0.5 MeV/atom. The defect depth profiles are extracted from Rutherford backscattering spectrometry and channeling. The depth profile of carbon is extracted from secondary ion mass spectrometry measurements. The defect density produced by dimer ions is larger than monomer ions. The depth profile of carbon in dimer implanted GaAs is deeper than that of monomer implanted GaAs showing negative molecular effect. The defect depth profile of oxygen dimer implanted GaAs is deeper for 3+ than that for 1+ charge state. This indicates that energy loss of O{sub 2}{sup 3+} is smaller than that of O{sub 2}{sup +}. It is attributed to charge asymmetry and a higher degree of alignment of O{sub 2}{sup 3+} along the [100] axis of GaAs.Quantum phases of hard core bosons (HCBs) confined in a one-dimensional quasiperiodic (QP) potential are studied within the theoretical framework of Hanbury-Brown-Twiss interferometry. The QP potential induces a cascade of Mott-like band-insulator phases in the extended regime, in addition to the Mott insulator, Bose glass, and superfluid phases. The new phases are incompressible and have zero superfluid fraction. At critical filling factors, the appearance of these insulating phases is heralded by a peak to dip transition in the interferogram, which reflects the fermionic aspect of HCBs. In the localized phase, the interference pattern exhibits an hierarchy of peaks at the reciprocal lattice vectors of the system. Our study demonstrates that in contrast to the momentum distribution, HBTI provides an effective method to distinguish Mott and glassy phases.The double autoionization rate for the He{sup -}(2s{sup 2}2p {sup 2}P) hollow atom state is calculated using a nonperturbative time-dependent close-coupling method. The nine-dimensional wave function for the three electron atom is expanded in coupled spherical harmonics. The time-dependent Schroedinger equation is then reduced to a set of close-coupled partial differential equations for the three-dimensional radial expansion functions. Relaxation in imaginary time subject to orthogonality constraints yields a 2s{sup 2}2p {sup 2}P hollow atom state with real energy, while propagation in real time yields total and double Auger rates. The total Auger rate is in reasonable agreement with previous saddle-point complex-rotation calculations. The double Auger rate is found to be 10% of the total Auger rate, in keeping with the relatively large double to total ratio found in recent experiments for He{sup -}(2s2p{sup 2} {sup 4}P)Electron impact ionization cross sections (EIICS) of 30 L-shell targets, with open- and closed-shell configurations in the isoelectronic sequences ranging from Li to Ne, are evaluated using the generalized parameters of our recent modification of BELL formula (MBELL) [Haque et al., Phys. Rev. A 73, 012708 (2006)]. Three sets of parameters, one each for the 1s, 2s, and 2p orbits, provide an excellent account of the experimental EIICS data of atomic targets, neutral and ionic, up to the atomic number Z=92 and incident energies up to about 250 MeV. In comparison with the quantum mechanical predictions, it is found that the present MBELL cross sections are in better agreement with the experimental results.Absolute photoionization cross-section measurements for a mixture of ground and metastable states of Xe{sup 4+}, Xe{sup 5+}, and Xe{sup 6+} are reported in the photon energy range of 4d{yields}nf transitions, which occur within or adjacent to the 13.5 nm window for extreme ultraviolet lithography light source development. The reported values allow the quantification of opacity effects in xenon plasmas due to these 4d{yields}nf autoionizing states. The oscillator strengths for the 4d{yields}4f and 4d{yields}5f transitions in Xe{sup q+} (q=1-6) ions are calculated using nonrelativistic Hartree-Fock and random phase approximations. These are compared with published experimental values for Xe{sup +} to Xe{sup 3+} and with the values obtained from the present experimental cross-section measurements for Xe{sup 4+} to Xe{sup 6+}. The calculations assisted in the determination of the metastable content in the ion beams for Xe{sup 5+} and Xe{sup 6+}. The experiments were performed by merging a synchrotron photon beam generated by an undulator beamline of the Advanced Light Source with an ion beam produced by an electron cyclotron resonance ion source.Conventional quantum key distribution (QKD) protocols include a basis selection process for providing a secure secret key. In contrast, this paper proposes an entanglement-based QKD with no basis selection procedure. Entangled-photon pulse trains with an average photon number less than one per pulse are sent to two legitimate parties, from which a secret key is created utilizing the entanglement nature. Eavesdropping on a transmission line is prevented by a condition of less than one photon per pulse, and sending classically correlated coherent pulses instead of quantum correlated ones is revealed by monitoring coincident count rate000.Second-harmonic generation is studied for the case where the fundamental field is light produced in a spontaneous parametric down-conversion process. We show that second-harmonic generation is sensitive to the transverse correlations between signal and idler fields. In particular, when the fundamental is prepared in a state exhibitting spatial antibunching, the second-harmonic intensity may be zero, independent of the intensity of the fundamental field.Multielectron processes have been studied by measuring the Na{sup 2+} and Na{sup 3+} recoil momenta resulting from 10 keV/amu He{sup 2+}+Na(3s) collisions. The Na{sup 2+} Q-value spectrum shows that transfer ionization dominates two-electron removal. Double capture populates mostly singly excited He(1snl) states. A smaller fraction of double capture leads to doubly excited He. Na{sup 3+} recoil ions are created by double capture into the He ground state and the emission of a third electron into the continuum. The Na{sup 3+} recoil ion is not left in its triplet ground state but in one of the low-lying excited singlet terms due to spin conservation.We have determined the lifetime of the Li-like {sub 22}{sup 48}Ti 1s2s2p {sup 4}P{sub 5/2}{sup o} level (210.5{+-}13.5 ps) using data from its x-ray decay channel through beam single- and two-foil experiments, coupled to a multicomponent iterative growth and decay analysis. Theoretical lifetime estimates for this zero-nuclear-spin ion lies within the uncertainty range of our experimental results, indicating that blending contributions to this level from the He-like 1s2p {sup 3}P{sub 2}{sup o} and 1s2s {sup 3}S{sub 1} levels are eliminated within the current approach. A previously reported discrepancy between experimental and theoretical 1s2s2p {sup 4}P{sub 5/2}{sup o} level lifetimes in {sub 23}{sup 51}V may, as a result, be attributed to hyperfine quenching.Orientation effects for electron transfer in keV He{sup 2+}-H{sub 2}{sup +} collisions are calculated based on a semiclassical close coupling model which accurately describes the electronic dynamics. When direct processes dominate it is shown that a configuration where the molecule is perpendicular to the ion momentum is always most favorable. At lower collision energies, rotational couplings and important contributions from low impact parameters can lead to dominant capture cross sections from molecular target aligned parallel with the collision beam.We formulate an expression for the accessible information in mirror-symmetric ensembles of real qubit states. This expression is used to make a detailed study of optimum quantum measurements for extracting the accessible information in three-state, mirror-symmetric ensembles. Distinct measurement regimes are identified for these ensembles with optimal measurement strategies involving different numbers of measurement operators, similar to results found for minimum error discrimination. Our results generalize known results for the accessible information in two pure states and in the trine ensemble.We propose a method to control population transfer and coherence in a multimode system using a transform-limited pump and a linearly chirped Stokes pulse in stimulated Raman scattering. Simultaneously applied pump and Stokes pulse are shown to induce the ac Stark shifts that result in nonadiabatic coupling of the dressed states, through which the pulse chirp governs population distribution. The method may be applied to selectively excite Raman transitions having the frequency difference less than the bandwidth of a transform-limited pulse.We investigate the properties of the vortex-antivortex superposed state for a Bose-Einstein condensate confined in a harmonic potential. The density distribution of the vortex-antivortex superposed state has a petal structure which is determined by the quantum circulations and proportion of the vortex and antivortex. Based on the Gross-Pitaevskii equation, we show that this vortex-antivortex superposed state can be stable through both analytical derivation and numerical calculations. Furthermore, we propose a feasible scheme to generate a coherently superposed vortex-antivortex state with arbitrary proportion by compressing and rehabilitating the harmonic trap with specific time order, which is proven by numerical simulations.The electric-field-dependent g factor of the ground state of {sup 2}{pi}{sub 1/2} molecules is predicted cross zero at a specific value of electric field. Furthermore, Edg/dE evaluated at this field is expected to be small, allowing for extremely precise zeroing of the molecular magnetic moment. For the PbF molecule, we estimate this field to be 68 kV/cm. If this prediction is correct, PbF could provide a uniquely sensitive probe of the electric dipole moment of the electron.The lifetimes of three isotopologs of the molecular hydrogen anion have been measured using an electrostatic ion-beam trap. Much longer lifetimes (up to {approx}2 ms for D{sub 2}{sup -}) than predicted by the most recent calculation are found, and it is proposed that more than one electronic state contributes to the overall lifetimes of these species.We have measured the absolute energy-averaged cross section for the electron impact excitation of C{sup 2+}(2s2p {sup 3}P{sup o}{yields}2p{sup 2} {sup 3}P) from energies below threshold to 17 eV above, and present the measured absolute rate coefficients for this transition, for temperatures from 10{sup 4} to 10{sup 5} K. These rate coefficients are required for diagnostics of plasmas such as those found in astrophysical environments. The synchronous photon detection method with beams modulation and inclined electron and ion beams was used. Radiation at 117.6 nm from the decay of the excited ions back to the metastable state was detected using an absolutely calibrated optical system. The fractional population of metastable C{sup 2+}(2s2p {sup 3}P{sup o}) in the incident ion beam was determined to be 0.42{+-}0.03(1.65 {sigma}). The rate coefficient for log{sub 10} T=4.8 was determined to be 1.01x10{sup -8} cm{sup 3} s{sup -1}{+-}14% at a 90% confidence (1.65 {sigma}) level. The measured cross section is in agreement within experimental uncertainty with 6-term close-coupling R-matrix calculations and 90-term R matrix with pseudostates calculations.In a Bose-Einstein condensate of {sup 87}Rb (F=2,m{sub F}=2) atoms we have topologically created a quantized vortex with a charge of 4 by reversing the magnetic field of the trap. Experimental conditions of reversal time and initial magnetic field strength for the successful vortex creation were restricted within narrower ranges, compared to those in the case of the {sup 23}Na condensate. The experimental difficulty was explained in terms of a non-negligible gravitational sag arising from its large atomic mass. We have successfully stabilized the vortex formation by compensating gravity with a blue-detuned laser beam.In this study we evaluate the cross section for forming the nonrelativistically bound state of a positron with the helium triplet atom by radiative attachment. Although this cross-section was expected to be small compared with a competing rearrangement process involving positronium and ground-state helium, this calculation is a first step which should be useful for experimental production of this interesting system.We analyze coherence effects during the splitting of a quasi one-dimensional condensate into two spatially separated ones and their subsequent merging into a single condensate. Our analysis takes into account finite-temperature effects, where phase fluctuations play an important role. We show that, at zero temperature, the two split condensates can be merged into a single one with a negligible phase difference. By increasing the temperature to a finite value below the critical point for condensation (T{sub c}), i.e., 0{<=}T/T{sub c}<1, a considerable enhancement of phase and density fluctuations appears during the process of splitting and merging. Our results show that if the process of splitting and merging is sufficiently adiabatic, the whole process is quite insensitive to phase fluctuations and even at high temperatures, a single condensate can be produced.A simple scheme is proposed to generate an n-qubit W state in cavity QED. Conditioned on no photon leakage from the cavity, the n-qubit W state can be generated by resonant interaction between atoms and the cavity if the cavity is initially prepared in the single-photon state and all the atoms are in the ground states. We check the time evolution of the system involving decay, and show that, since the required interaction time is very short, with present cavity QED techniques, the success probability of our scheme is almost unity.We consider the development of pairing in an ideal Fermi gas in the presence of a time-dependent BCS interaction. The pairing amplitude time evolution is controlled by the interplay of linear instability of the unpaired state and nonlinear interactions which limit the growth. This results in oscillatory time dependence with predictable characteristics, selecting periodic soliton trains of a specific form, described by a Jacobi elliptic function. While the parameters of the soliton train, such as the period, amplitude, and time lag, fluctuate among different realizations, the elliptic function form remains robust. The parameter fluctuations are accounted for by the randomness of particle distribution in the initial unpaired state.We present a theoretical treatment of the surprisingly large damping observed recently in one-dimensional Bose-Einstein atomic condensates in optical lattices. We show that time-dependent Hartree-Fock-Bogoliubov (HFB) calculations can describe qualitatively the main features of the damping observed over a range of lattice depths. We also derive a formula of the fluctuation-dissipation type for the damping, based on a picture in which the coherent motion of the condensate atoms is disrupted as they try to flow through the random local potential created by the irregular motion of noncondensate atoms. When parameters for the characteristic strength and correlation times of the fluctuations, obtained from the HFB calculations, are substituted in the damping formula, we find very good agreement with the experimentally observed damping, as long as the lattice is shallow enough for the fraction of atoms in the Mott insulator phase to be negligible. We also include, for completeness, the results of other calculations based on the Gutzwiller ansatz, which appear to work better for the deeper lattices.The angular dependence of dissociative electron attachment (DEA) to polyatomic targets is formulated in the local complex potential model, under the assumption that the axial recoil approximation describes the dissociation dynamics. An additional approximation, which is found to be valid in the case of H{sub 2}O but not in the case of H{sub 2}S, makes it possible to describe the angular dependence of DEA solely from an analysis of the fixed-nuclei entrance amplitude, without carrying out nuclear dynamics calculations. For H{sub 2}S, the final-vibrational-state-specific angular dependence of DEA is obtained by incorporating the variation of the angular dependence of the entrance amplitude with nuclear geometry into the nuclear dynamics. Scattering calculations using the complex Kohn method and, for H{sub 2}S, full quantum calculations of the nuclear dynamics using the multiconfiguration time-dependent Hartree method, are performed.We introduce a family of linear maps which are positive but not completely positive. We exhibit examples of nondecomposable maps and 2{sup N}x2{sup N}, N{>=}2, bound entangled states - e.g., nondistillable bipartite states of N+N qubits. Such states, as the standard Bell diagonal states, are diagonal in a maximally entangled basis and, apart remaining positive under partial transposition, are not detected by the realignment criterion.We have used an electron beam ion trap to observe a visible line at 598.30(13) nm that corresponds to the 4d{sup 9} {sup 2}D{sub 3/2}-4d{sup 9} {sup 2}D{sub 5/2} magnetic dipole transition within the ground state configuration of Xe{sup 9+}. We have found no evidence to support the claim by others that a line near this position originates from Xe{sup 31+}. The comparison of the measured wavelength with previous indirect experimental values, and the dependence of the line intensity on the electron beam energy, confirms the validity of the present identification. Our measured wavelength is in agreement with semiempirical Hartree-Fock calculations but shows a discrepancy with ab initio multiconfiguration Dirac-Fock calculations. We propose that the line may be useful as a diagnostic for extreme ultraviolet lithography light sources.We show that the complex scaling method for resonances is equivalent to carrying out a gedanken experiment, where particles are scattered by a target with the incoming flux not being constant as usual but exponentially reduced in time at the rate {gamma}. Resonances are examined at discrete energy levels, while a counterintuitive reverse dynamical control is demonstrated off these levels for {gamma} greater than the resonance decay rate {gamma}{sub r}.In this paper we describe an application of fermion molecular dynamics to the simulation of the behavior of H{sub 2}{sup +} and H{sub 2} immersed in a strong laser field. The laser field consists of a single short pulse of linearly polarized long wavelength radiation; viz., t{sub pulse}{approx}100 fs, {lambda}=758 nm, and 10{sup 13}{<=}I{sub 0}<10{sup 14} W/cm{sup 2}. Results are compared with data from recent laboratory measurements.Using the known perturbation series for the idempotent Dirac density matrix in powers of a given one-body potential V(r), Stoddart and March (SM) generated a corresponding series for the kinetic energy density. While the general term of the SM series is known, a summation has not been achieved to date. A contribution to solve this problem is made here by exhibiting an explicit form of the above kinetic energy density for Fermions filling an arbitrary number of closed shells, when the confinement is harmonic. This example is of considerable current interest because of ongoing experiments on ultracold atomic gases of Fermions.A modified version of the Moeller-Plesset approach for obtaining the correlation energy associated with a Hartree-Fock ground state is proposed. The method is tested in a model of interacting fermions that allows for an exact solution. Using up to third order terms improved results are obtained, even in the limit of loosely bound particles. Tested in molecules as well, the modified method appears to give improved results in symmetric systems.We investigate quantum properties of phase-locked light beams generated in a nondegenerate optical parametric oscillator (NOPO) with an intracavity waveplate. This investigation continues our previous analysis presented in Phys. Rev. A 69, 053814 (2004), and involves problems of continuous-variable quadrature entanglement in the spectral domain, photon-number correlations as well as the signatures of phase-locking in the Wigner function. We study the role of phase-localizing processes on the quantum correlation effects. The peculiarities of phase-locked NOPO in the self-pulsing instability operational regime are also cleared up. The results are obtained in the P-representation as a quantum-mechanical calculation in the framework of stochastic equations of motion, as well as by numerical simulation based on the method of quantum state diffusion.The best three-channel projectile-inelastic close-coupling approximation (CCA) is used to study the resonances in positronium (Ps) and hydrogen (H) scattering at the energy region below the inelastic threshold. The s-wave elastic phase shifts and s-wave elastic cross sections are studied using the static-exchange, two- and three-channel projectile-inelastic CCA for both the singlet (+) and triplet (-) channels. The singlet resonances detected using different CCA schemes confirm previous predictions [Drachman and Houston, Phys. Rev. A 12, 885 (1975); Page, J. Phys. B. 9, 1111 (1976)]. We report a resonance in the triplet channel too using the present three-channel CCA scheme.Results of a theoretical study of photoionization cross sections and photoelectron angular asymmetry parameters of atoms confined by positively C{sub 60}{sup +z} or negatively C{sub 60}{sup -z} charged fullerene shells are presented. For negatively charged C{sub 60}, entirely new confinement resonances, termed Coulomb confinement resonances, that dominate the spectra of the encapsulated atoms are predicted. In addition, the effect of a negative C{sub 60} shell is to move some of the oscillator strength of the encapsulated atom from the discrete excitation region into the continuum. For positively charged C{sub 60}, the situation is much different; no Coulomb confinement resonances occur in the photoionization spectrum of the encapsulated atom, and charging the shell positively does nothing to the photoionization cross section (as a function of photon energy) except to increase the threshold energy. The findings result from model Hartree-Fock calculations of 1s photoionization of Ne confined by neutral, negative, and positive C{sub 60}.A new nuclear quadrupole moment, Q=0.305(2) b, of {sup 87}Sr is determined by combining precise measurement of the electric quadrupole hyperfine structure constant of the 4d {sup 2}D{sub 5/2} state of its ion with calculation. This is a significant improvement over the previous values 0.335(20), 0.327(24), and 0.323(20) b. Relativistic coupled-cluster theory is employed in the calculations and electron correlation effects are included using the single, double, and an important subset of triple excitations. The magnetic dipole and electric quadrupole hyperfine structure constants of a few low-lying states are calculated to a high accuracy. The role of different electron correlation effects in the 4d {sup 2}D{sub 5/2} state is investigated.Within the context of quantum teleportation, a proposed interpretation of bipartite entanglement describes teleportation as consisting of a qubit of information evolving along and against the flow of time of an external observer. We investigate the physicality of such a model by applying time reversal to the Schroedinger equation in the teleportation context. To do so, we first present the theory of time reversal applied to the circuit model. We then show that the outcome of a teleportationlike circuit is consistent with the usual tensor product treatment and is therefore independent of the physical quantum system used to encode the information. Finally, we illustrate these concepts with a proof-of-principle experiment on a liquid-state NMR quantum-information processor. The experimental results are consistent with the interpretation that information can be seen as flowing backward in time through entanglement.Absolute K-shell ionization and L{alpha} and L{beta}{sub 1} x-ray production cross sections for Ga and As have been measured for incident electrons in the energy range from 1.5 to 39 keV. The cross sections were deduced from K{alpha}, L{alpha}, and L{beta}{sub 1} x-ray intensities emitted from ultrathin GaAs samples deposited onto self-supporting carbon films. The x-ray intensities were measured on an electron microprobe equipped with several wavelength-dispersive spectrometers and were converted into absolute cross sections by using estimated values of the target thickness, spectrometer efficiency, and number of incident electrons. Experimental results are compared with cross sections calculated from the plane-wave and distorted-wave Born approximations, the relativistic binary-encounter-Bethe model, the results of two widely used simple analytical formulas, and, whenever possible, experimental data from the literature.Using the experimental data on the energy-level shift of kaonic hydrogen in the ground state [Beer et al., Phys. Rev. Lett. 94, 212302 (2005)] and the theoretical value of the energy-level shift, calculated within the phenomenological quantum field theoretic approach to the description of strong low-energy KN and KNN, interactions, we estimate the value of the {sigma}{sub KN}{sup (I=1)}(0) term of low-energy KN scattering. We get {sigma}{sub KN}{sup (I=1)}(0)=433{+-}132 MeV. This shows the absence of strange quarks in the proton structure.The nonrelativistic ground-state energy of {sup 4}HeH{sup +} is calculated using a variational method in Hylleraas coordinates. Convergence to a few parts in 10{sup 10} is achieved, which improves the best previous result of Pavanello et al. [J. Chem. Phys. 123, 104306 (2005)]. Expectation values of the interparticle distances are evaluated. Similar results for {sup 3}HeH{sup +} are also presented.

Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL

We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.