Magnetically trapped neutral atoms can be cooled with the evaporation technique. This is typically done by using a radio-frequency (rf) field that adiabatically couples trapped and untrapped internal atomic states for atoms with kinetic energies above a value set by the field frequency. The rf field can also induce nonadiabatic changes of internal atomic spin states $\mathrm{}(F,M)\mathrm{}$ that lead to heating and enhanced loss of atoms. In this paper we use wave-packet simulations to show that the evaporation process can induce these nonadiabatic transitions, which change the internal spin state of doubly spin-polarized (2,2) trapped atoms. We also verify the validity of a multistate Landau-Zener model in describing the nonadiabatic dynamics. In addition, we calculate exchange relaxation rate coefficients for collisions between atoms in the $\mathrm{}(2,M)\mathrm{}$ states of ${}^{23}\mathrm{Na}$ atoms. Large exchange relaxation coefficients for ${}^{23}\mathrm{Na}$ as compared to ${}^{87}\mathrm{Rb}\hspace{0.5em}F=2\mathrm{}$ suggest that evaporative cooling of (2,2) Na will be more difficult than for the corresponding state of Rb.

We report on spin precession experiments using a ${}^7\mathrm{Li}$ atomic beam, which offers a perturbation-free environment to investigate spin dynamics under the influence of external fields. The ground-state magnetic moments perform a Larmor precession in a “fictitious magnetic field” induced by an off-resonant, circularly polarized laser beam. For a fictitious magnetic field parallel to a real one, we observe additional rotation of the spins, whereas an echo is observed if both fields are perpendicular with respect to each other. The systematics of these phenomena are studied.

We calculate the reflection probability for ultracold sodium atoms incident on an evanescent-wave atomic mirror. For low enough energies the reflection probability curves exhibit quantum effects that are sensitive to the long-range part of the potential and can therefore be used to resolve Casimir retardation effects. We also explore the accuracy of model potentials approximating the exact atom-wall effective potential.

We report on the use of an efficient stepwise-resonant two-photon excitation scheme to study high principal quantum number even-parity $\mathrm{}\left(2pnp\right)\mathrm{}$ Rydberg states of atomic carbon. This scheme uses intense vacuum ultraviolet light to drive the resonance transition of the atoms, followed by excitation to Rydberg states with tunable ultraviolet light. Atomic carbon was produced under high vacuum conditions using laser ablation. Analysis of the spectrum of the unperturbed $J=3\mathrm{}$ Rydberg series below and above the first ionization limit yielded a new value for the ionization potential of the atom, with an accuracy primarily limited by the accuracy with which the intermediate state energy is known. The spectra of the $J=0,$ 1, and 2 Rydberg states all displayed the effects of coupling between different series converging to the two fine-structure states of the ion core. These spectra have been successfully reproduced using ab initio R-matrix calculations.

One electron bound by a three-dimensional two-center zero-range potential is embedded in an electric field with sinusoidal time dependence and arbitrary polarization and orientation with respect to the axis of the two-center potential. In the absence of the field, the model supports up to two bound states, which have a large transition dipole moment. Hence, the physical systems best described by the model are molecular ions such as ${\mathrm{H}}_2^{+}.$ Rates for high-harmonic emission are calculated analytically up to one final quadrature. In terms of the rescattering picture, harmonic emission can be attributed to two different mechanisms: electrons recombine either at the center they started from or at the other one. The latter case allows for three topologically different classes of orbits, which lead to different spectral ranges of harmonics. Two of them are similar to atomic (one-center) harmonic generation, but have different cutoff laws that are no longer proportional to the ponderomotive potential. In the third the electron moves directly from one center to the other. This leads to strong harmonic emission at comparatively low frequencies similar to emission from a two-level atom with the cutoff proportional to the field amplitude rather than the intensity. The molecular dipole phase in this case is almost independent of the field intensity and, at constant intensity, the phases of neighboring harmonics are locked. Different orientations of the two-center system with respect to the field with various polarization configurations are investigated. Most of the observed features lend themselves to interpretation in terms of the simple man’s model.

A double atom interferometer based upon the Stern-Gerlach method in which the first interferometer acts as a “nonordinary” source for the second one is described. Experiments have been carried out with a wide-velocity-distribution beam of metastable hydrogen atoms, using two different operating modes: (i) continuous mode in which the magnitude of the magnetic field in the first interferometer is fixed whereas that of the second one is scanned; (ii) time-of-flight mode in which both magnetic fields are fixed. In the former case lateral interference patterns appear, in the latter one an overmodulation of the time-of-flight distribution is observed. It is predicted that this overmodulation becomes more and more marked as the number of interferometers is increased, leading to a limiting behavior characteristic of a quantum Zeno effect.

We study hydrodynamic oscillations of a cylindrical Bose gas above the Bose-Einstein transition temperature using the hydrodynamic equations derived by Griffin, Wu, and Stringari. This extends recent studies of a cylindrical Bose-condensed gas at $T=0.\mathrm{}$ Explicit normal mode solutions are obtained for non-propagating solutions. In the classical limit, the sound velocity is shown to be the same as a uniform classical gas. We use a variational formulation of the hydrodynamic equations to discuss the propagating modes in the degenerate Bose-gas limit and show there is little difference from the classical results. We discuss the propagation of sound pulses above and below $T_{\mathrm{BEC}}.$

We have developed a compact closed-form solution of the band transport model for high-contrast gratings in photogalvanic crystals. Our solution predicts the effect of the photoconductivity and the electric field grating enhancement due to the photogalvanic effect. We predict a pronounced dependence of the steady-state photogalvanic current on the contrast of the interference pattern and an increase of holographic storage time due to the enhancement of the photoconductivity grating contrast. In the high contrast limit and a large photogalvanic effect the refractive index grating will be shifted from the position of the intensity modulation pattern, contrary to the usually adopted model of unshifted gratings.

One of the canonical questions in quantum optics is the nature of the radiative properties of an atom when the normal vacuum fluctuations of the electromagnetic reservoir are replaced by the asymmetric, reduced fluctuations of a squeezed vacuum. While the basic radiative linewidth-narrowing effect has been known for over a decade [C. W. Gardiner, Phys. Rev. Lett. 56, 1917 (1986)], experimental realizations with operationally definable definitive manifestations of the quantum nature of the squeezed reservoir have been largely lacking from subsequent investigations. This paper presents measurements on an experimentally realized atom–squeezed-light system, in which the squeezed-light output of a subthreshold optical parametric oscillator illuminates an atom strongly coupled to a high-finesse optical resonator. Transmission of a weak probe field incident on the atom-cavity system is investigated both theoretically and experimentally. Alteration of the transmitted probe spectrum has been observed, as has a transmission modulation that depends on the phase of the squeezed field relative to a saturating coherent field (displaced squeezing). In certain parameter regimes, properties unique to the quantum nature of the squeezed light have been identified in the theoretical treatment, but complications in the experiment prevent their unequivocal measure. It is found that the observed effects of the squeezed light are dramatically reduced relative to the predictions of an idealized theory. This is quantitatively attributed to the effects of atomic beam fluctuations and a simple modeling of the atomic beam as an additional loss mechanism in the theory leads to reasonable agreement with the data.

An approximate solution is given for the interaction of a set of $A$ two-level atoms with a single mode of a quantized radiation field when the field is damped by a reservoir at zero temperature. Assuming that the average photon number is much larger than the number of atoms, we study the influence of dissipation on the approximate factorization of the density matrix. For realistic values of the parameters, the factorization survives under the presence of field damping. The main effect of dissipation is an exponential decay of the average photon number and a loss of coherence among the different factorized states. The influence of field dissipation on the atomic inversion, purity, and field squeezing are studied.

We study the dynamical squeezing of the photon-added coherent state (PACS) due to a time dependence of the frequency of the electromagnetic field oscillator in a cavity or a vibrational frequency of an ion inside an electromagnetic trap. Explicit expressions for the time dependence of various functions characterizing the quantum state, such as the photon distribution, the Wigner function, the mean values and variances of the quadrature components and of the photon number, show that the dynamically squeezed PACS possesses a larger squeezing coefficient than the usual squeezed states. The dynamical squeezing is accompanied by a change of the sub-Poissonian photon statistics to the super-Poissonian one.

We investigate the population differences between ground-state hyperfine levels (${5S}_{1/2},F=2\mathrm{}$ and ${5S}_{1/2},$ $F=1\mathrm{}$) of an optically pumped ${}^{87}\mathrm{Rb}$ beam in a static magnetic field, taking into account the various kinds of atomic coherence (Zeeman, hyperfine, and optical). The pumping lasers are monochromatic and in resonance with the ${(5S}_{1/2},F=1\mathrm{}\leftrightarrow {5P}_{1/2}{,F}^{\prime }=1)$ transition. By varying the polarization configuration of the pumping lasers, we find that the pumping efficiency is substantially enhanced when a $\sigma$-polarized laser and a $\pi$-polarized laser are counterpropagating. In this case, the pumping efficiency remains high even in a weak magnetic field, which explains qualitatively experimental data reported previously from a cesium beam experiment.

Using tunable ultraviolet picosecond laser pulses pump-probe degenerate four-wave mixing (DFWM) and polarization spectroscopy experiments were conducted in atmospheric pressure flames to investigate the temporal signal behavior in selected rotational transitions of the OH $A{}^2\Sigma –X{}^2\Pi \hspace{0.5em}\mathrm{}(0,0)\mathrm{}$ electronic band. The relaxation behavior of simultaneously excited main and satellite transitions in the Q and P branches was studied in premixed stoichiometric methane-air and hydrogen-oxygen flames. Experimental signal traces are compared with expressions from a detailed theoretical treatment of the signal generation process using perturbation calculations. The theoretical approach consists in calculating the energy density in the signal field mode taking into account the frequency spread of the pump and probe beam radiation, collisional relaxation effects, and the polarization configuration of the incident beams. Relaxation times for population and orientation deduced from the fitting algorithm are in good agreement with DFWM line-shape studies [S. Williams et al., J. Chem. Phys. 104, 3947 (1996)]. It is shown that quantitative agreement with experimental data obtained for different polarization configurations of pump, probe, and signal photons can be achieved when appropriate time correlated interactions of pump and probe photons are taken into account. In addition, it is shown that due to the frequency spread of the employed laser pulses the different frequency components in the signal beam contribute with different amplitude to the oscillating and nonoscillating parts in the temporal development of the signal intensity depending on the relative strength of the simultaneously excited transitions.

Strong evidence indicating the occurrence of electromagnetically induced transparency (EIT) in a solid medium was found. Fluorescence reduction due to EIT was observed in solids. The excitation intensity dependence of the fluorescence reduction was found to be consistent with theoretical predictions for EIT. It was experimentally demonstrated that the essential condition for the observation of EIT in solids is that the Rabi frequency of excitation must be larger than the inhomogeneous width of the transition between the two states coupled to the third state by the pair of optical fields.

We report experiments that investigate the generation of coherent VUV radiation at 123.6 nm via a resonant sum-difference frequency mixing scheme in Kr. One of the mixing fields at 212.55 nm was in two-photon resonance with the transition between the ${4p}^6{}^{1}S$ ground state and the ${4p}^{5}5p[0,\frac{1}{2}]$ excited state $\left(94\mathrm{}093.7\hspace{0.5em}{\mathrm{cm}}^{-1}\right).\mathrm{}$ The second field (the coupling field) at 759 nm was in single-photon resonance with the transition between the ${4p}^{5}5p[0,\frac{1}{2}]$ state and the ${4p}^{5}5s[1,\frac{1}{2}]$ state at $80917.6\hspace{0.5em}{\mathrm{cm}}^{-1}.$ The presence of the coupling field leads to electromagnetically induced transparency (EIT) at the wavelength of the generated field, 123.6 nm. This is predicted to enhance the four-wave-mixing efficiency by a large factor. We have studied the dependence of the four-wave mixing process on the detuning and strength of the coupling field. The efficiency for four-wave mixing was found to be enhanced by a significant factor (>5) by the EIT effect when the resonant coupling field strength exceeded about half the Doppler width $\left(0.1\mathrm{}\hspace{0.5em}{\mathrm{cm}}^{-1}\right).\mathrm{}$ A calculation for monochromatic fields and a uniform slab of gas provided qualitative agreement with the results of experiment. The relative conversion efficiency for this resonant mixing scheme is found to be ${10}^4$ times greater than that for a similar scheme where the coupling laser is tuned far $\left(1270\mathrm{}\hspace{0.5em}{\mathrm{cm}}^{-1}\right)$ off resonance. A substantial part of this resonant enhancement can thus be attributed to the EIT effect.

It is known that there is a transition from photon antibunching to bunching in the resonance fluorescence of a driven system of two two-level atoms with dipole-dipole interaction when the atomic distance decreases and the other parameters are kept fixed. We give a simple explanation for the underlying mechanism that in principle can also be applied to other systems.

The generation of radiation pulses that can be as short as 120 attoseconds is demonstrated theoretically. We have employed a two-dimensional exact solution of the Schrödinger equation that allows for arbitrary laser ellipticity. By manipulating the laser ellipticity in time, it is shown that one can control the wave-packet dynamics of the ejected atomic electron. The nonlinear interaction of the electron with the atomic core can thus be restricted to extremely short times. Photon energies up to 160 eV are generated. It is also shown that with a higher laser frequency, even shorter pulses can be produced.

We analyze the possibility of creating photons from a vacuum due to the dynamical Casimir effect in a nondegenerate cavity with vibrating boundaries, taking into account losses and detuning from the exact resonance. Explicit analytical solutions of the equations for the quadrature variances of an equivalent field oscillator with a time-dependent frequency show that photon generation is possible provided the relative detuning and inverse quality factor do not exceed a critical value of the order of ${10}^{-8}.$ Under this condition, the field goes finally to a highly squeezed quantum state.

We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler-broadened medium. Nanosecond SF pulses at 5.5 μm were generated on the Ca $4s4p{}^1{P}_1–3d4s{}^1{D}_2$ transition from a column of calcium vapor buffered with Ar by optically pumping the ${4s}^2{}^1{S}_0–4s4p{}^1{P}_1$ transition. The Rabi frequency associated with the intense pump pulse prevents the occurrence of SF while the pump laser is on. As a result, the predicted scaling laws that describe the properties of SF in a transversely excited system, such as peak heights, pulse widths, and delay times, are shown to apply in our situation in which the conditions resemble swept excitation. The delay times were found to be in agreement with a fully quantum mechanical calculation which describes the initiation of SF. Measurements of the densities of the three levels, the absolute SF photon yield, and the spatial distribution of the excited states indicate that the system has a quantum yield of unity. The SF intensity increases with an increase in Ar pressure due to collisional redistribution until the collisional dephasing rate inhibits SF. The conditions describing the transition of SF to amplified spontaneous emission allow us to measure the collisional broadening rate for the SF transition.

An interferometric arrangement utilizing a pair of twin photons, generated by parametric down-conversion, is devised to show second-order interferences revealing de Broglie’s wavelength of the photon pair as a whole and the Pancharatnam phase depending on the number of photons. This proposed experiment utilizes the phenomenon “induced coherence without stimulated emission” to generate a coherent superposition of states distinct from the usual superposition with beam splitters, where the photons are independently scattered. In this experiment interference occurs due to recombination of photon trajectories on a beam splitter and also through frustration or enhancement of the down-conversion processes.