We demonstrate confinement of ${}^{85}\mathrm{Rb}$ atoms in a dark, toroidal optical trap. We use a spatial light modulator to convert a single blue-detuned Gaussian laser beam to a superposition of Laguerre-Gaussian modes that forms a ring-shaped intensity null bounded harmonically in all directions. We measure a $\mathrm{\dots }$

[Phys. Rev. A 76, 061404(R)] Published Fri Dec 28, 2007

We report on the Stark deceleration and electrostatic trapping of ${}^{14}\text{N}\text{H}$ $\left(a{}^1\Delta \right)$ radicals. In the trap, the molecules are excited on the spin-forbidden $A{}^3\Pi \leftarrow a{}^1\Delta$ transition and detected via their subsequent fluorescence to the $X{{}^3\Sigma }^{-}$ ground state. The $1∕e$ trapping time is $1.4\pm 0.1\text{s}$, from which a lower limit…

[Phys. Rev. A 76, 063408] Published Thu Dec 27, 2007

We present measurements of the internal state distribution of electrostatically guided formaldehyde. Upon excitation with continuous tunable ultraviolet laser light the molecules dissociate, leading to a decrease in the molecular flux. The population of individual guided states is measured by addres…

[Phys. Rev. A 76, 061402(R)] Published Thu Dec 20, 2007

We report measurements of both the phase and intensity of high-order harmonic emission from aligned ${\mathrm{CO}}_2$ molecules, using a mixture of a molecular and an atomic gas. The molecules are transiently aligned using an ultrashort pulse, and a subsequent stronger pulse is used to generate high-order harmoni…

[Phys. Rev. A 76, 061403(R)] Published Thu Dec 20, 2007

The theory of measurement projection operators in grid-based time-dependent wave-packet calculations involving electronic continua in atoms and molecules is discussed. A hierarchy of projection operators relevant in their individual restricted configuration spaces is presented. At asymptotically lar…

[Phys. Rev. A 76, 063407] Published Tue Dec 18, 2007

We study high-order harmonic generation in ${\mathrm{C}}_{60}$ molecules interacting with a linearly polarized intense short laser pulse at near- and mid-infrared wavelengths, using an extension of the so-called three-step or Lewenstein model to the molecular case. The results exhibit modulations in the plateaus of…

[Phys. Rev. A 76, 063406] Published Fri Dec 14, 2007

We present optimal control, using femtosecond laser pulses in a closed-loop experiment, of the ionization process of ultracold rubidium molecules formed in a magneto-optical trap. The resulting spectrum of the optimally shaped pulse exhibits two frequency bands, which drive a resonantly enhanced thr…

[Phys. Rev. A 76, 063404] Published Wed Dec 12, 2007

We describe an efficient technique for calculating cross sections for two-photon single and double ionization of an atom without the use of the final-state continuum wave function. We present results of an application to helium over the photon energy range $25-54\text{eV}$, and we compare our results to a r…

[Phys. Rev. A 76, 063405] Published Wed Dec 12, 2007

We investigate the effect of incoherent perturbations on atomic photoionization due to a femtosecond midinfrared laser pulse by solving the time-dependent stochastic Schrödinger equation. For a weak laser pulse which causes almost no ionization, an addition of a Gaussian white noise to the pulse lea…

[Phys. Rev. A 76, 063403] Published Thu Dec 06, 2007

We have studied the velocity distribution of chromium atoms released from a solid neon matrix at cryogenic temperatures via Doppler spectroscopy. The Ne matrix is grown by directing a small flux of gas onto a cold substrate, while Cr atoms are simultaneously implanted by laser ablation, with the res…

[Phys. Rev. A 76, 061401(R)] Published Tue Dec 04, 2007

An optical pumping scheme is presented that uses incoherent Raman transitions to prepare a trapped cesium atom in a specific Zeeman state within the $6S_{1/2}$, $F=3$ hyperfine manifold. An important advantage of this scheme over existing optical pumping schemes is that the atom can be prepared in any of t…

[Phys. Rev. A 76, 063401] Published Mon Dec 03, 2007

Two contrasting physical viewpoints and calculational approaches are adopted within the framework of molecular quantum electrodynamics for the evaluation of the static contribution to the change in mutual interaction energy between a pair of electric dipole polarizable molecules in an intense radiat…

[Phys. Rev. A 76, 063402] Published Mon Dec 03, 2007

We observe velocity-selective two-photon resonances in a cold atom cloud in the presence of a magnetic field. We use these resonances to demonstrate a simple magnetometer with sub-mG resolution. The technique is particularly useful for zeroing the magnetic field and does not require any additional l…

[Phys. Rev. A 76, 053421] Published Thu Nov 29, 2007

Subnatural linewidth in an optical transition in Cs was obtained by the suppression and recovery of the trapping of atoms. Cold Cs atoms in a magneto-optical trap (MOT) were irradiated using a weak probe laser to suppress MOT loading. When a counterpropagating coupling laser was directed to be reson…

[Phys. Rev. A 76, 055404] Published Thu Nov 29, 2007

Doubly dressed states in a ladder-type two-photon, three-level coupling system are observed. The electromagnetically induced transparency (EIT) doublet signal is interpreted as arising from the absorption and gain components of the Mollow spectrum. The separation of the EIT doublet matches the theor…

[Phys. Rev. A 76, 053420] Published Wed Nov 28, 2007

Numerical simulations have revealed that by adding a second harmonic field to a laser field with a time-dependent ellipticity, single isolated attosecond pulses can be generated as a result of the combined power of the two-color gating and the polarization gating. The duration of the pump laser appl…

[Phys. Rev. A 76, 051403(R)] Published Tue Nov 27, 2007

We investigate cooling mechanisms in magneto-optically and magnetically trapped erbium. We find efficient sub-Doppler cooling in our trap, which can persist even in large magnetic fields due to the near degeneracy of two Landé $g$ factors. Furthermore, a continuously loaded magnetic trap is demonstrat…

[Phys. Rev. A 76, 053418] Published Tue Nov 27, 2007

We study in detail coherent phase control of femtosecond resonance-mediated $\left(2+1\right)$ three-photon absorption and its dependence on the spectral bandwidth of the excitation pulse. The regime is the weak-field regime of third perturbative order. The corresponding interference mechanism involves a group o…

[Phys. Rev. A 76, 053419] Published Tue Nov 27, 2007

We investigate the temporal dynamics of Doppler cooling of an initially hot single trapped atom in the weak-binding regime using a semiclassical approach. We develop an analytical model for the simplest case of a single vibrational mode for a harmonic trap, and show how this model allows us to estim…

[Phys. Rev. A 76, 053416] Published Mon Nov 26, 2007

We discuss the properties of ultracold Rydberg atoms in a Ioffe-Pritchard magnetic field configuration. The derived two-body Hamiltonian unveils how the large size of Rydberg atoms affects their coupling to the inhomogeneous magnetic field. The properties of the compound electronic and center of mas…

[Phys. Rev. A 76, 053417] Published Mon Nov 26, 2007

Photoassociation of a pair of cold atoms by excitation with a short chirped laser pulse creates a dynamical hole in the initial continuum wave function. This hole is manifested by a void in the pair wave function and a momentum kick. Photoassociation into loosely bound levels of the external well in…

[Phys. Rev. A 76, 053415] Published Wed Nov 21, 2007

Optical trapping of selected species of radioactive atoms has great potential in precision measurements for testing fundamental physics such as the electric dipole moment, atomic parity nonconservation, and parity-violating $\beta$-decay correlation coefficients. We report on the trapping of ${10}^4$ radioacti…

[Phys. Rev. A 76, 051402(R)] Published Tue Nov 20, 2007

Ultrafast and narrow linewidth lasers are combined to study multiphoton photoassociative ionization (PAI) in a Rb magneto-optical trap. Through the use of time of flight spectroscopy and by varying the parameters of the ultrafast laser, the excitation pathway for PAI was determined. It was found tha…

[Phys. Rev. A 76, 051401(R)] Published Mon Nov 19, 2007

Intrashell transitions in Rydberg atoms with a nonhydrogenic core were studied. The degeneracy of the energy shell was lifted by constant electric and magnetic fields and transitions from initial coherent elliptic states (CES) were driven by a harmonic electric field. Evenly spaced hydrogenic resona…

[Phys. Rev. A 76, 053414] Published Mon Nov 19, 2007

A classical ensemble is employed to investigate double ionization of helium for laser wavelength 390 nm and intensity $1.1\text{PW}∕{\text{cm}}^2$, below the threshold for recollision impact ionization. Significant numbers of trajectories that lead to electron energy above $2U_p$ are shown to be present and to feature a…

[Phys. Rev. A 76, 053412] Published Fri Nov 16, 2007

We investigate the rotational dynamics of heteronuclear diatomic molecules possessing a ${{}^1\Sigma }^{+}$ electronic ground state exposed to a strong external time-dependent homogeneous electric field. An exponential switching on and off is employed for the electric field. We analyze the orientation and hybridiza…

[Phys. Rev. A 76, 053413] Published Fri Nov 16, 2007

A general ab initio and nonperturbative method to solve the time-dependent Schrödinger equation (TDSE) for the interaction of a strong attosecond laser pulse with a general atom, i.e., beyond the models of quasi-one-electron or quasi-two-electron targets, is described. The field-free Hamiltonian and…

[Phys. Rev. A 76, 053411] Published Thu Nov 15, 2007

The very pronounced intensity-dependent enhancements of groups of peaks of high-order above-threshold-ionization spectra of rare-gas atoms are investigated using an improved version of the strong-field approximation, which realistically models the respective atom. Two types of enhancements are found…

[Phys. Rev. A 76, 053410] Published Wed Nov 14, 2007

The ionization of nonsymmetric heteronuclear diatomic molecules by intense few-cycle laser pulses linearly polarized along the internuclear axis has been investigated. It is found that enhanced ionization (EI) occurs in nonsymmetric molecules and is accompanied by enhanced excitation (EE). We show t…

[Phys. Rev. A 76, 053409] Published Tue Nov 13, 2007

Ultracold photoassociation is a process in which two cold atoms combine to form a molecule. This process is crucially dependent on the atom pair density at close distance termed the photoassociation window. We explore the possibilities for increasing the pair density at the photoassociation window b…

[Phys. Rev. A 76, 053408] Published Mon Nov 12, 2007

Within the framework of the relativistic quantum theory the multiphoton above-threshold ionization (ATI) of hydrogenlike atoms in the field of super-strong electromagnetic radiation of linear polarization, taking into account the photoelectron stimulated bremsstrahlung (SB) on the residual ion, is i…

[Phys. Rev. A 76, 053406] Published Fri Nov 09, 2007

Theoretical analysis of the Autler-Townes splitting pattern in a three-level cascade excitation of a Doppler-broadened sample reveals that the observed Autler-Townes splitting is not only a function of the coupling-laser Rabi frequency, as in the homogeneously broadened case, but can also strongly d…

[Phys. Rev. A 76, 053407] Published Fri Nov 09, 2007

The photoionization spectrum of an atom in a magnetic field is calculated by combining $R$-matrix propagation with local adiabatic basis expansions. This approach considerably increases the speed and the energy range over which calculations can be performed compared to previous methods, allowing one t…

[Phys. Rev. A 76, 053405] Published Thu Nov 08, 2007

We demonstrate loading of ${}^{88}\mathrm{Sr}^{+}$ ions by laser ablation into a mm-scale surface-electrode ion trap. The laser used for ablation is a pulsed, frequency-tripled Nd:YAG with pulse energies of $1–10\mathrm{mJ}$ and durations of $4\mathrm{ns}$. An additional laser is not required to photoionize the ablated material. The effici…

[Phys. Rev. A 76, 055403] Published Thu Nov 08, 2007

In this paper, the problem of achieving an arbitrary $\text{SU}\left(1,1\right)$ coherent state is considered via switching the control field back and forth between admissible values with minimal number of switching times. When the controlled system Hamiltonian is hyperbolical or parabolical, the results show that the …

[Phys. Rev. A 76, 053403] Published Tue Nov 06, 2007

We present an analytically exactly soluble two-state model, in which a hyperbolic-secant-shaped pulsed interaction has a phase jump of $\varphi$ at the time of its maximum. The detuning has a constant part and a hyperbolic-tangent chirp term. For $\varphi =0$, this model reduces to the Demkov-Kunike model, which in …

[Phys. Rev. A 76, 053404] Published Tue Nov 06, 2007

We show that magnetic-field-induced circular differential deflection of light can be observed in reflection or refraction at a single interface. The difference in the reflection or refraction angles between the two circular polarization components is a function of the magnetic-field strength and the…

[Phys. Rev. A 76, 055402] Published Tue Nov 06, 2007

We have observed the phase lag in the sinusoidal variation of the asymmetric photoelectron angular distributions into two ionization channels of atomic barium using an $\omega \text{−}2\omega$ excitation scheme. We excite atomic barium from the $6s6p{{}^{1}P}_1$ intermediate state electron to an energy between the $5d_{3∕2}ϵ$ and th…

[Phys. Rev. A 76, 053401] Published Mon Nov 05, 2007

Tunnel ionization of room-temperature ${\mathrm{D}}_2$ in an ultrashort (12 femtosecond) near infrared $\left(800\mathrm{nm}\right)$ pump laser pulse excites a vibrational wavepacket in the ${{\mathrm{D}}_2}^{+}$ ions; a rotational wavepacket is also excited in residual ${\mathrm{D}}_2$ molecules. Both wavepacket types are collapsed a variable time later by an ultras…

[Phys. Rev. A 76, 053402] Published Mon Nov 05, 2007

A recent work on two-photon fluorescence is extended by considering the pump field to be a coherent state, which represents a laser field operating well above threshold. The dynamical conditions are investigated under which the two-photon spectrum gives rise, in addition to a Lorentzian line shape a…

[Phys. Rev. A 76, 055401] Published Mon Nov 05, 2007

We numerically study the implementation of a NOT gate by laser pulses in a model molecular system presenting two electronic surfaces coupled by nonadiabatic interactions. The two states of the bit are the fundamental states of the cis-trans isomers of the molecule. The gate is classical in the sense…

[Phys. Rev. A 76, 043424] Published Tue Oct 30, 2007

An investigation of field-free molecular alignment produced by elliptically polarized laser pulses is reported. Experiments are conducted in ${\text{CO}}_2$ at room temperature. A noninvasive all-optical technique, based on the cross defocusing of a probe pulse, is used to measure the alignment along two orthog…

[Phys. Rev. A 76, 043423] Published Mon Oct 29, 2007

Dynamics of multilevel molecules and pulse propagation is studied near the two-photon resonance. We have found a strict solution of this problem beyond the rotating wave approximation. Our analytical solution is in close agreement with the strict numerical solution for the $4,4^{\prime }$-bis(dimethylamino) st…

[Phys. Rev. A 76, 043422] Published Thu Oct 25, 2007

We produce large numbers of low-energy ions by photoionization of laser-cooled atoms inside a surface-electrode-based Paul trap. The isotope-selective trap’s loading rate of $4\times {10}^5{\mathrm{Yb}}^{+}\mathrm{ions}∕\mathrm{s}$ exceeds that attained by photoionization (electron-impact ionization) of an atomic beam by three (six) orders o…

[Phys. Rev. A 76, 041401(R)] Published Wed Oct 24, 2007

A method is described for extracting double ionization amplitudes from a quantum wave packet for an atom after a short radiation pulse, but while the electrons are still interacting. The procedure involves the use of exterior complex scaling to effectively propagate the field-free solution to infini…

[Phys. Rev. A 76, 043420] Published Wed Oct 24, 2007

Tunable, polarized, microfocused x-ray pulses were used to record x-ray absorption spectra across the $K$ edges of ${\text{Kr}}^{+}$ and ${\text{Kr}}^{2+}$ produced by laser ionization of Kr. Prominent $1s\to 4p$ and $5p$ excitations are observed below the $1s$ ionization thresholds in accord with calculated transition energies and proba…

[Phys. Rev. A 76, 043421] Published Wed Oct 24, 2007

Using a quantum-mechanical three-step model, we present numerical calculations of the high-order harmonic generation from four polyatomic molecules. Ethylene $\left({\text{C}}_2{\text{H}}_4\right)$ serves as an example where orbital symmetry directly affects the harmonic yield. We treat the case of methane $\left({\text{CH}}_4\right)$ to address the high…

[Phys. Rev. A 76, 043419] Published Fri Oct 19, 2007

The Siegert-state expansion approach is applied to the solution of the time-dependent Schrödinger equation describing a model one-dimensional laser-atom interaction problem in the Kramers-Henneberger frame. Our method is mathematically rigorous and numerically exact even though a very restricted spa…

[Phys. Rev. A 76, 043418] Published Wed Oct 17, 2007

In the strong-field approximation, we calculate the electron momentum distribution following strong-field ionization of atomic hydrogen by an $N$-cycle circularly polarized laser pulse. For $N\lesssim 5$, our results show a pronounced interference structure in addition to the well-known carrier-envelope phase d…

[Phys. Rev. A 76, 043416] Published Tue Oct 16, 2007

We report the experimental observation of temporal quantum interference between two time-delayed 3S-3P-5S (or 4D) transition pathways created through two collision-assisted two-step excitation processes by using a single nanosecond laser pulse in the ${\mathrm{Na}}_2\text{−}\mathrm{Na}$ system. It is clearly shown that the colli…

[Phys. Rev. A 76, 043417] Published Tue Oct 16, 2007

This paper presents state-selective field ionization spectra of highly excited Rydberg states of NO. The competition between electron-nuclear coupling and electron-field coupling is investigated and it is shown that the slew rate of the electric field can be exploited to control the rotational quant…

[Phys. Rev. A 76, 043413] Published Fri Oct 12, 2007

We propose a technique which produces nearly complete ionization of the population of a discrete state coupled to a continuum by a two-photon transition via a lossy intermediate state whose lifetime is much shorter than the interaction duration. We show that using counterintuitively ordered pulses, …

[Phys. Rev. A 76, 043414] Published Fri Oct 12, 2007

We investigate the effect of temperature on resonant and antiresonant dynamics in a dilute atomic gas kicked periodically by a standing-wave laser field. Our numerical calculations are based on a Monte Carlo method for an incoherent mixture of noninteracting plane waves, and show that the atomic dyn…

[Phys. Rev. A 76, 043415] Published Fri Oct 12, 2007

We report the laser cooling and confinement of Cd atoms in a magneto-optical trap and characterize the loading process from the background Cd vapor. The trapping laser drives the ${}^{1}S_0\to {}^{1}P_1$ transition at $229\mathrm{nm}$ in this two-electron atom and also photoionizes atoms directly from the ${}^{1}P_1$ state. This photo…

[Phys. Rev. A 76, 043411] Published Thu Oct 11, 2007

We present an ab initio three-dimensional (3D) calculation of multiphoton ionization (MPI) and high-order harmonic generation (HHG) of the hydrogen molecular ions subject to intense linearly polarized laser pulses. The orientation of the molecular axis with respect to the polarization of the laser f…

[Phys. Rev. A 76, 043412] Published Thu Oct 11, 2007

We investigated the coherence accumulation in Rb atoms excited by a train of femtosecond pulses. The coherence accumulation results in the velocity selective optical pumping of Rb hyperfine levels, observed by a cw probe laser. The effects of the pulse train excitation on the cw probe laser transmis…

[Phys. Rev. A 76, 043410] Published Wed Oct 10, 2007

We perform a detailed analysis of high-order harmonic generation in diatomic molecules within the strong-field approximation (SFA), with emphasis on quantum-interference effects. Specifically, we investigate how the different types of electron orbits, involving one or two centers, affect the interfe…

[Phys. Rev. A 76, 043407] Published Tue Oct 09, 2007

In the field of optical trapping and micromanipulation it is well known that linearly polarized Gaussian beams, which possess no inherent angular momentum, can exert an orienting torque on optically or geometrically anisotropic particles. Conservation of angular momentum requires that the applicatio…

[Phys. Rev. A 76, 043408] Published Tue Oct 09, 2007

In this paper, we present a detailed investigation of the laser cooling and trapping of the Zn atom, and various schemes employing the ${{}^{1}S}_0\text{−}{{}^{3}P}_0$ transition, induced by nuclear magnetic moment or applied fields, as the clock transition. Using numerical simulations, the deceleration of Zn by a Zeeman sl…

[Phys. Rev. A 76, 043409] Published Tue Oct 09, 2007

We propose that micrometer-sized atom traps can be created using the optical dipole force between the ends of two single-mode optical fibers carrying counterpropagating light beams of two different wavelengths from both fibers. The traps have a simple design that is feasible to implement with commer…

[Phys. Rev. A 76, 043404] Published Mon Oct 08, 2007

We have developed an ab initio $R$-matrix-based approach for the time-dependent description of the multielectron response of complex atoms irradiated by intense ultrashort laser pulses. Ionization rates for Ar irradiated by intense $390\mathrm{nm}$ laser light are in excellent agreement with the most accurate ra…

[Phys. Rev. A 76, 043405] Published Mon Oct 08, 2007

Doppler cooling on narrow transitions has become a crucial technique for preparing ultracold samples of alkaline-earth-metal and alkaline-earth-metal-like atoms. For lighter species, such as calcium and magnesium, this technique relies on artificial broadening (quenching) of the upper level of the n…

[Phys. Rev. A 76, 043406] Published Mon Oct 08, 2007

A method to prepare nonclassical states of the motion of a trapped ion that interacts with a traveling wave light field has been proposed, which is based on modulation of the frequency of the traveling wave field. In the end, an experiment configuration about its preparation is proposed and discusse…

[Phys. Rev. A 76, 043403] Published Fri Oct 05, 2007

We analyzed the two-dimensional (2D) electron momentum distributions of high-energy photoelectrons of atoms in an intense laser field using the second-order strong field approximation (SFA2). The SFA2 accounts for the rescattering of the returning electron with the target ion to first order and its …

[Phys. Rev. A 76, 043402] Published Thu Oct 04, 2007

We analyze carrier-envelope phase (CEP) effects on electron wave-packet momentum and energy spectra produced by one or two few-cycle attosecond xuv pulses. The few-cycle attosecond pulses are assumed to have arbitrary phases. We predict CEP effects on ionized electron wave-packet momentum distributi…

[Phys. Rev. A 76, 043401] Published Mon Oct 01, 2007

We demonstrate an efficient scheme for continuous trap loading based upon spatially selective optical pumping. We discuss the case of ${}^{1}S_0$ calcium atoms in an optical dipole trap (ODT), however, similar strategies should be applicable to a wide range of atomic species, which do not permit efficient c…

[Phys. Rev. A 76, 033418] Published Fri Sep 28, 2007

In contrast to the long-wavelength regime, x-ray nonlinear optical processes are characterized in general by sequential single-photon single-electron interactions. Despite this fact, the sequential absorption of multiple x-ray photons depends on the statistical properties of the radiation field. Tre…

[Phys. Rev. A 76, 033416] Published Thu Sep 27, 2007

In the framework of the state-specific expansion approach, we have solved nonperturbatively the time-dependent Schrödinger equation for systems involving the time-dependent excitation of nonstationary states by hypershort one or two electromagnetic pulses. The related problems concern the quantitati…

[Phys. Rev. A 76, 033417] Published Thu Sep 27, 2007

The ionization dynamics of $\mathrm{H}_2{}^{+}$ in an intense xuv laser pulse is studied beyond the dipole approximation in fields of linear and circular polarization. Our theoretical work shows distinct signatures of new ionization mechanisms and subsequent dynamics. Both low- and high-energy electrons emerge from …

[Phys. Rev. A 76, 033415] Published Wed Sep 26, 2007

Through multiphoton ionization measurements, the polarization effects in destructive quantum interference under three-photon resonant excitation have been studied. Recent observations [V. Peet, Phys. Rev. A 74, 033406 (2006)] have indicated that contrary to the well-known pattern of a total suppress…

[Phys. Rev. A 76, 035402] Published Tue Sep 25, 2007

We propose a method of manipulating selectively the symmetric Dicke subspace in the internal degrees of freedom of $N$ trapped ions. We show that the direct access to ionic-motional subspaces, based on a suitable tuning of motion-dependent ac Stark shifts, induces a two-level dynamics involving previo…

[Phys. Rev. A 76, 033413] Published Mon Sep 24, 2007

We present a simple quantum mechanical model to describe Coulomb explosion of $\mathrm{H}_2{}^{+}$ and $\mathrm{D}_2{}^{+}$ by short, intense infrared laser pulses. The model is based on the length gauge version of the molecular strong-field approximation and is valid when the process of dissociation prior to ionization is negligibl…

[Phys. Rev. A 76, 033414] Published Mon Sep 24, 2007

When molecules interact with light sources of femtosecond or shorter duration the rotational degrees of freedom are frozen during the response to the strong nonperturbative interaction. We analytically derive how the frozen degrees of freedom affect the measurable signals in high-order harmonic gene…

[Phys. Rev. A 76, 035401] Published Mon Sep 24, 2007

We describe a technique based upon the principles of two-pathway coherent control that allows one to amplify the magnitude of a weak atomic or molecular transition. In our initial demonstrations, we amplify a weak Stark-induced transition (the $6s{{}^{2}S}_{1∕2}\to 8s{{}^{2}S}_{1∕2}$ transition in atomic cesium) by cohere…

[Phys. Rev. A 76, 033412] Published Thu Sep 20, 2007

The polarization of high-order harmonic radiation emitted from ${\mathrm{N}}_2$ molecules interacting with a linearly polarized laser pulse is investigated theoretically. We find that the exchange effect between the recombining electron and the bound core electrons imprints a clear signature onto the high-order h…

[Phys. Rev. A 76, 031404(R)] Published Wed Sep 19, 2007

We present a strategy for optimal control of the ground-state dynamics in multidimensional systems based on a combination of the semiclassical Wigner distribution approach with direct quantum chemical molecular dynamics (MD) “on the fly.” This allows one to treat all degrees of freedom without the n…

[Phys. Rev. A 76, 031405(R)] Published Wed Sep 19, 2007

We have realized a two-dimensional permanent magnetic lattice of Ioffe-Pritchard microtraps for ultracold atoms. The lattice is formed by a single $300\text{−}\mathrm{nm}$ magnetized layer of FePt, patterned using optical lithography. Our magnetic lattice consists of more than 15 000 tightly confining microtraps with…

[Phys. Rev. A 76, 033408] Published Wed Sep 19, 2007

We consider a system composed of a trapped atom and a trapped ion. The ion charge induces in the atom an electric dipole moment, which attracts it with an $r^{-4}$ dependence at large distances. In the regime considered here, the characteristic range of the atom-ion interaction is comparable or larger th…

[Phys. Rev. A 76, 033409] Published Wed Sep 19, 2007

We describe a technique for mapping the spatial variation of static electric, static magnetic, and rf magnetic fields using a pulsed atomic or molecular beam. The method is demonstrated using a beam designed to measure the electric dipole moment of the electron. We present maps of the interaction re…

[Phys. Rev. A 76, 033410] Published Wed Sep 19, 2007

We have measured motional heating rates of trapped atomic ions, a factor that can influence multi-ion quantum logic gate fidelities. Two simplified techniques were developed for this purpose: one relies on Raman sideband detection implemented with a single laser source, while the second is even simp…

[Phys. Rev. A 76, 033411] Published Wed Sep 19, 2007

We experimentally investigate one-dimensional (1D) expansion of a cold cloud of cesium atoms in orthogonal 2D configuration of near resonant laser beams by temporally modulating a pair of counterpropagating trapping beams of a magneto-optical trap (MOT). The cloud is observed to undergo ballistic ex…

[Phys. Rev. A 76, 033407] Published Tue Sep 18, 2007

We consider the dynamic escape of a small packet of ultracold atoms launched from within an optical dipole trap. Based on a theoretical analysis of the underlying nonlinear dynamics, we predict that fractal behavior can be seen in experimental escape data. These data can be collected by measuring th…

[Phys. Rev. A 76, 031403(R)] Published Mon Sep 17, 2007

By solving nonperturbatively the equations of Schrödinger and of Hamilton, we have studied the time-dependent multiphoton dissociation of a diatomic molecule induced by a moderate low-frequency laser field. The photodissociation probabilities are calculated and analyzed as a function of the laser fr…

[Phys. Rev. A 76, 033406] Published Mon Sep 17, 2007

Using a three-dimensional semiclassical method, we perform a systematic analysis of the effects of an additional static electric field on nonsequential double ionization (NSDI) of a helium atom in an intense, linearly polarized laser field. It is found that the static electric field influences not o…

[Phys. Rev. A 76, 033405] Published Fri Sep 14, 2007

The effect of an intense external linearly polarized radiation field on the angular distributions and polarization states of the photons emitted during the radiative capture of a free electron by a bare nucleus into the ground state of the bound system is investigated. On symmetry grounds it is pred…

[Phys. Rev. A 76, 031402(R)] Published Thu Sep 13, 2007

A recent experimental study of the photodetachment of negative fluorine ions by a strong, circularly polarized laser field has been used as a test case for comparison of different gauges in a strong-field theory. Earlier studies concluded that the length gauge was the more suitable theory, but it wa…

[Phys. Rev. A 76, 033404] Published Mon Sep 10, 2007

In the customary formulation of the strong-field approximation (SFA) for laser-induced ionization, the initial bound state is taken as field-free. In the formulation of a length-gauge SFA for ionization of a molecule described by a two-center binding potential with sufficiently large internuclear se…

[Phys. Rev. A 76, 033403] Published Wed Sep 05, 2007

We report the results of a study of the effects of combined electric and magnetic fields on dielectronic recombination (DR) from a continuum of finite bandwidth. Specifically, we have examined the process $\mathrm{Ba}6p_{3∕2}8g\to \mathrm{Ba}6p_{1∕2}nk\to \mathrm{Ba}6s_{1∕2}nk+h\nu$ in the presence of electric fields from $0\text{to}7\mathrm{V}∕\mathrm{cm}$ and magnetic …

[Phys. Rev. A 76, 031401(R)] Published Tue Sep 04, 2007

We study quantum systems with even numbers $N$ of levels that are completely state controlled by unitary transformations generated by Lie algebras isomorphic to $\mathrm{sp}\left(N\right)$ of dimension $N(N+1)∕2$ as discussed by Albertini and D’Allesandro [IEEE Trans. Autom. Control 48, 1399 (2003)]. These Lie algebras are s…

[Phys. Rev. A 76, 033401] Published Tue Sep 04, 2007

We present a theoretical framework for the electronic dynamics of arbitrarily oriented molecular hydrogen in strong and short electromagnetic fields. The ground state of ${\mathrm{H}}_2$ is obtained by propagating the time-dependent Schrödinger equation in imaginary time by assuming the Hartree-Fock ansatz for th…

[Phys. Rev. A 76, 033402] Published Tue Sep 04, 2007

We discuss the general problem of generating confining potentials for neutral matter by combining different kinds of static forces. The interactions taken into account are those having a linear or quadratic dependence on the modulus of an irrotational and solenoidal field. Particular attention is de…

[Phys. Rev. A 76, 023428] Published Fri Aug 31, 2007

A numerical simulation of photodetachment of ${\mathrm{F}}^{-}$ by a circularly polarized laser pulse has been accomplished by using a Keldysh-type approach. The numerical results are in agreement with measurements of photoelectron energy spectra recently reported in the literature. The features exhibited by the sp…

[Phys. Rev. A 76, 021401(R)] Published Thu Aug 30, 2007

The time and momentum distributions of electron emission from a molecule during a single laser cycle are calculated by solving a two-dimensional time-dependent Schrödinger equation. The momentum distributions strongly depend on the orbital symmetry and orientation of the molecular axis. Field-induce…

[Phys. Rev. A 76, 023426] Published Thu Aug 30, 2007

Different descriptions of the light-matter interaction which include the full spatial dependence of the electromagnetic field are presented. It is demonstrated how nondipole forms of both the Kramers-Henneberger and the length gauge Hamiltonians may be obtained from the minimum-coupling Hamiltonian …

[Phys. Rev. A 76, 023427] Published Thu Aug 30, 2007

The theory of laser cooling assisted by transverse magnetic field ${\mathbf{B}}_{\mathbf{t}}$ based on the $(1+3)$-level atomic system is presented. With the additional ${\mathbf{B}}_{\mathbf{t}}$, atoms could be redistributed among the upper Zeeman sublevels via Larmor precession, and results in large stimulated radiation force and low temperature. …

[Phys. Rev. A 76, 023425] Published Wed Aug 29, 2007

The quantum resonances of an atom possessing a single valence electron which shows hyperfine interaction with the nucleus is investigated in the presence of a three-dimensional magnetic quadrupole field. Particular emphasis is put on the study of the interplay of the hyperfine and quadrupole forces.…

[Phys. Rev. A 76, 023424] Published Tue Aug 28, 2007

We present convergent-close-coupling (CCC) calculations of the angular anisotropy parameters ${\beta }_2,{\beta }_4$ and the recoil ion momentum distribution $d\sigma ∕d\mathit{p}$ in two-photon double ionization (TPDI) of helium. In a stark contrast to single-photon double ionization (SPDI), where the ${\beta }_2$ parameter varies widely chan…

[Phys. Rev. A 76, 025402] Published Tue Aug 28, 2007

Electron detachment from negative ions by few-cycle laser pulses is considered. The results of a full numerical solution of the time-dependent Schrödinger equation are compared to those from several analytic approaches. A nonmonotonic dependence of the detachment probability on the pulse duration at…

[Phys. Rev. A 76, 023423] Published Mon Aug 27, 2007

We study the dynamics of a dilute Bose-Einstein condensate confined in a toroidal trap and exposed to a pair of periodically flashed optical lattices. We first prove that in the noninteracting case this system can present a quantum symmetry which forbids the ratchet effect classically expected. We t…

[Phys. Rev. A 76, 023421] Published Fri Aug 24, 2007

A weak resonant femtosecond pulse propagates through an optically thick atomic medium whose properties have been modified by a strong nonresonant ultrashort pulse. We study the energy redistribution between the spectral components of the weak resonant pulse using both experimental and theoretical me…

[Phys. Rev. A 76, 023422] Published Fri Aug 24, 2007