We report on Doppler-free frequency modulation spectroscopy and polarization spectroscopy in a discharge heat pipe of yet unexplored transitions connecting the metastable ${}^{3}P_2\left(4s4p\right)$ state of calcium atoms with the multiply excited states ${}^{3}P_2\left(4p4p\right)$ and ${}^{3}D_3\left(4s3d\right)$. Calcium vapor is efficiently produced in a heat pipe operating in a small Pyrex cell filled with $2\text{torr}$ of neon. A dc discharge running at $500\mathrm{V}$ efficiently populates the metastable triplet states. Narrow resonances with bandwidths of a few tens of MHz with excellent signal-to-noise ratios are observed, well suited as references for laser frequency stabilization. Examination of the Zeeman shifts lets us determine the Landé $g$ factors of the excited states and compare them with the predictions based on the Russel-Saunders coupling scheme. We describe an economic, simple, and robust experimental setup that should work for other alkaline-earth-metal atoms like Mg and Sr, as well as for other solid elements with insufficient vapor pressures at room temperature.

A method is described for estimating effective scattering lengths via spectroscopy on a trapped pair of atoms. The method relies on the phenomena that the energy levels of two atoms in a harmonic trap are shifted by their collisional interaction. The amount of shift depends on the strength of the interaction (i.e., scattering length). By combining the spectra of the trap state energy levels and a suitable model for the effective scattering length, an estimate for the latter may be inferred. Two practical methods for measuring the trap spectra are proposed and illustrated in examples. The accuracy of the scheme is analyzed and requirements on measurement precision are given.

Efficient and long-lived field-free molecular orientation is achieved using only two kicks appropriately delayed in time. The understanding of the mechanism rests upon a molecular target state providing the best efficiency versus persistence compromise. An optimal control scheme is referred to for fixing the free parameters (amplitudes and the time delay between them). The limited number of kicks, the robustness and the transposability to different molecular systems advocate in favor of the process, when considering its experimental feasibility.

An accurate study of the lowest $1{\sigma }_g$ and the low-lying excited $1{\sigma }_u,1{\pi }_{u,g},1{\delta }_{g,u}$ electronic states of the exotic molecular ion $\mathrm{H}_3{}^{2+}$ in linear configuration parallel to a magnetic field is carried out. The magnetic field ranges from ${10}^{10}\mathrm{G}$ up to $4.414\times {10}^{13}\mathrm{G}$, where nonrelativistic considerations are justified. The variational method is exploited and the same trial function is used for different magnetic fields. It is shown that the states of positive $z$ parity $1{\sigma }_g,1{\pi }_u,1{\delta }_g$ are bound states of the $\mathrm{H}_3{}^{2+}$ exotic ion: the state $1{\sigma }_g$ exists for magnetic fields $B\gtrsim {10}^{10}\mathrm{G}$, and the states $1{\pi }_u,1{\delta }_g$ exist for $B\gtrsim 2.35\times {10}^{10}\mathrm{G}$. It is demonstrated that for magnetic fields $B\gtrsim 2.35\times {10}^{12}\mathrm{G}$ the potential energy surface well corresponding to the $1{\sigma }_g$ state contains at least one longitudinal vibrational state. It is shown that the negative $z$-parity states $1{\sigma }_u,1{\pi }_g,1{\delta }_u$ are pure repulsive in the whole range of magnetic fields studied, $B={10}^{10}\text{–}4.414\times {10}^{13}\mathrm{G}$.

An optically dense, anisotropic cloud of ultracold atoms is used to observe recoil-induced resonances in the high-gain regime. Optical gains as large as 30 are realized, limited primarily by pump depletion. We demonstrate a light-amplified all-optical switch based on this effect. The switch exhibits contrasts exceeding 35 dB.

We consider a single particle which is bound by a central potential and obeys the Dirac equation in $d$ dimensions. We first apply the asymptotic iteration method to recover the known exact solutions for the pure Coulomb case. For a screened Coulomb potential and for a Coulomb plus linear potential with linear scalar confinement, the method is used to obtain accurate approximate solutions for both eigenvalues and wave functions.

This paper describes a quantum cellular automaton capable of performing universal quantum computation. The automaton has an elementary transition function that acts on Margolus cells of $2\times 2$ qubits, and both the “quantum input” and the program are encoded in the initial state of the system.

The relaxation of atomic polarization in buffer-gas-free, paraffin-coated cesium vapor cells is studied using a variation on Franzen’s technique of “relaxation in the dark” [Franzen, Phys. Rev. 115 850 (1959)]. In the present experiment, narrow-band, circularly polarized pump light, resonant with the Cs D2 transition, orients atoms along a longitudinal magnetic field, and time-dependent optical rotation of linearly polarized probe light is measured to determine the relaxation rates of the atomic orientation of a particular hyperfine level. The change in relaxation rates during light-induced atomic desorption (LIAD) is studied. No significant change in the spin relaxation rate during LIAD is found beyond that expected from the faster rate of spin-exchange collisions due to the increase in Cs density.

We investigate two-component boson systems by using their two individual average sizes and the distance between their centers as coordinates. We use zero-range interactions and include only relative $s$ waves. An effective potential is computed and discussed as a function of particle numbers and interaction strengths. Efimov conditions of two very large scattering lengths can arise if one component is a binary molecule. The corresponding atom-molecule interaction can then exhibit chaotic behavior. We present static and dynamic properties of an atom-molecule two-component system. We discuss the possible atom-molecule oscillations when all atoms are identical. The atomic number is then used as a collective coordinate and the cranking mass is computed. The collective oscillation frequency is estimated and compared with the trap frequency and the three-body recombination rate.

We discuss details of momentum transfer in the interaction between localized atoms and localized optical fields which are relevant to precision atom interferometry. Specifically, we consider a $\Lambda$-type atom coherently driven between its ground states by a bichromatic optical field. We assume that the excited state can be eliminated adiabatically from the time evolution. It is shown that the average recoil momentum is given by the phase gradient of the two-photon field at the “position” of the atom, provided that the optical field can be described by a function which is separable in position and time and that the atomic wave function is symmetric and well localized within the optical field envelope. The result does not require the optical fields to have a Gaussian spatial dependence. Our discussion provides the basis for the analysis of systematic errors in precision atom interferometry arising from optical wave-front curvature, wave-front distortion, and the Gouy phase shift of Gaussian beams. We apply our result to the atom interferometer experiment of Chu and co-workers which measures the fine-structure constant.

We report an experimental study of the control of molecular alignment of ${\mathrm{N}}_2$ by use of spectrally modulated pulses at an intensity regime below the intrinsic saturation of the alignment. By manipulating the relative timing of the alignment revival pattern arising from the even subset of the thermal ensemble as compared to the odd subset, we demonstrate that the angular distribution of the aligned molecule can be converted into planar delocalization at specific times. We also show that the angular focusing of the molecular axis can be switched off by applying a specific bipulse.

We have made an investigation on the $2s2p$ ${}^{1,3}P^o$ resonance states of helium embedded in dense plasma environments. A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charge particles. A correlated wave function consisting of a generalized exponential expansion has been used to represent the correlation effect. Resonance energies and widths for the doubly excited He embedded in plasmas with various Debye lengths are determined using the stabilization method by calculating the density of resonance states. The resonance energies and widths for various Debye parameters ranging from infinity to a small value for the lowest ${}^{1,3}P^o$ resonance states are reported.

We present a spectroscopy technique for studying cold-collision properties. The technique is based on the association and dissociation of ultracold molecules using a magnetically tunable Feshbach resonance. The energy and lifetime of a shape resonance are determined from a measurement of the dissociation rate. Additional spectroscopic information is obtained from the observation of a spatial interference pattern between an outgoing $s$ wave and $d$ wave. The experimental data agree well with the results from a model, in which the dissociation process is connected to a scattering gedanken experiment, which is analyzed using a coupled-channel calculation.

Double ionization of ground-state helium by the Compton scattering of a photon is calculated using the well-known product of three Coulomb waves (3C) wave function for the final double-continuum state of the atom and the Pluvinage wave function for the initial ground state (also a product of three Coulomb waves). The theoretical model fails to predict both the shape and the overall magnitude of the observed integrated cross section vs incident-photon energy. However, when the monopole part of the electron-photon interaction is removed by an ad hoc procedure, qualitative agreement is obtained, although the absolute size of the cross section is still almost an order of magnitude too large.

The key realization that led to the emergence of the new field of quantum information processing is that quantum mechanics, the theory that describes microscopic particles, allows the processing of information in fundamentally new ways. But just as in classical information processing, errors occur in quantum information processing, and these have to be corrected. A fundamental breakthrough was the realization that quantum error correction is in fact possible. However, most work so far has not been concerned with technological feasibility, but rather with proving that quantum error correction is possible in principle. Here we describe a method for filtering out errors and entanglement purification which is particularly suitable for quantum communication. Our method is conceptually new, and, crucially, it is easy to implement in a wide variety of physical systems with present-day technology and should therefore be of wide applicability.

We propose a robust and decoherence insensitive scheme to generate controllable entangled states of two three-level atoms interacting with an optical cavity and a laser beam. Losses due to atomic spontaneous transitions and to cavity decay are efficiently suppressed by employing fractional adiabatic passage and appropriately designed atom-field couplings. In this scheme the two atoms traverse the cavity-mode and the laser beam in opposite directions and become entangled in the free space outside the cavity. We also show that the coherence of a traveling atom can be transferred to the other one without populating the cavity mode.

We present a study on scattering of $100–1400\mathrm{eV}$ ${\mathrm{Ne}}^{+}$ ions off Mg, Al, Si, and P surfaces. Exit energy distributions and yields of single-scattered ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ne}}^{2+}$ were separately measured to investigate charge exchange mechanisms occurring at the onset of inelastic losses in binary hard collision events. At low incident energies, collisions appear elastic and projectile ion survival is dominated by nonlocal Auger-type neutralization involving the target valence band. However, once a critical $R_{\min }$ (distance of closest approach) is reached, three phenomena occur simultaneously: ${\mathrm{Ne}}^{2+}$ generation, reversal of the ${\mathrm{Ne}}^{+}$ yield trend, and inelastic losses in ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ne}}^{2+}$. $R_{\min }$ values for the ${\mathrm{Ne}}^{2+}$ turn-on agree very well with the $L$-shell overlap distances of the colliding partners, suggesting that electron transfer involving the highly promoted $4f\sigma$ molecular orbital (correlated to the Ne $2p$) at close internuclear distance $(\sim 0.5\mathrm{\AA })$ is responsible. For the ${\mathrm{Ne}}^{+}$ yield, a clear transition from nonlocal neutralization to $R_{\min }$-dependent collision induced neutralization was observed. Binary collision inelasticities $\left(Q_{\mathit{bin}}\right)$ were evaluated for ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ne}}^{2+}$ off Al and Si by taking into account electron straggling. Saturation-like behavior at $R_{\min }<0.5\mathrm{\AA }$ was seen for ${\mathrm{Ne}}^{+}$ $(Q_{\mathit{bin}}\sim 40–45\mathrm{eV})$ and ${\mathrm{Ne}}^{2+}$ $(68–75\mathrm{eV})$. These losses fit well with double promotion of ${\mathrm{Ne}}^0\to {\mathrm{Ne}}^{**}$ ($2p^{4}3s^2$, $41–45\mathrm{eV}$) and ${\mathrm{Ne}}^{+}\to {\mathrm{Ne}}^{+**}$ ($2p^{3}3s^2∕3s3p$, $69–72\mathrm{eV}$), followed by autoionization as the projectile leaves the surface region to give ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ne}}^{2+}$. In contrast, $Q_{\mathit{bin}}$ values for ${\mathrm{Ne}}^{2+}$ at the $+2$ turn-on were seen much lower ($35–40\mathrm{eV}$ off Al, $55–60\mathrm{eV}$ off Si) than that required for double promotion—eliminating the possibility that ${\mathrm{Ne}}^{2+}$ is only generated in double excitation of surviving ${\mathrm{Ne}}^{+}$. Thus single-electron excitation appears to be more important in the threshold region compared to the two-electron events seen at higher collision energies. In addition, the ${\mathrm{Ne}}^{+}\mathrm{P}$ system shows striking similarities with the other target cases from the perspective of a well-defined ${\mathrm{Ne}}^{2+}$ turn-on, continually increasing ${\mathrm{Ne}}^{2+}$ yield with impact energy, and inelasticity values which point to the same $4f\sigma$ excitation pathway. The decreasing $R_{\min }$ requirement for higher target $Z$ in terms of ${\mathrm{Ne}}^{2+}$ production has been confirmed for the Mg through P series, where hard collision excitation is governed by $L$-shell orbital overlaps.

In anticipation of upcoming experiments on two-photon double ionization of atoms and particularly helium, under strong short-wavelength radiation sources (45 eV), we present quantitative signatures of direct two-photon double ejection, in the photoelectron spectrum (PES) and the peak power dependence, that can be employed in the interpretation of related data. We show that the PES provides the cleanest signature of the process. An inflection (knee) in the laser power dependence of double ionization is also discernible, within a window of intensities that depends on the pulse duration and cross sections

Attosecond pulse trains (APT) are natural tools for controlling strong field processes, due to their periodicity and short duration. Here we present nonadiabatic calculations of the macroscopic harmonic signal created by a gas of helium atoms exposed to a strong infrared (IR) pulse in combination with an APT. We find that the harmonic yield can be enhanced by two to four orders of magnitude for the optimal delays between the IR and the APT pulses. The large enhancement is due to the change in the IR-intensity dependence of both the harmonic strength and phase caused by the presence and timing of the APT. This leads to enhancement of the harmonic yield and improved phase matching conditions over a large volume.

Motivated by recent experiments that demonstrated a strongly enhanced reflection efficiency of atoms on microfabricated, gratinglike surface structures, we develop a detailed description of the scattering of atomic matter waves on such structures. We start with a simple model that describes the ridged surface as an equivalent absorbing medium. This model correctly predicts the experimentally observed scaling and magnitude of the reflection efficiency. We then calculate the accurate solutions for the Fresnel diffraction of waves at grazing incidence at a periodic set of idealized, parallel edges. Both numerical and analytical solutions are presented. The specular reflectivity and its phase, as well as the efficiencies of higher diffraction orders are calculated. We compare our results to experimental data in a wide range of parameters. We extend the model including the finite size of the grating ridges and the van der Waals attraction and suggest a more general estimate of the reflection coefficient.