Nonlinear magneto-optical resonances occurring for near-zero magnetic field are studied in Rb vapor using light-noise spectroscopy. With a balanced detection polarimeter, we observe high contrast variations of the noise power (at fixed analysis frequency) carried by diode laser light resonant with the $5{\mathrm{S}}_{1∕2}\left(F=2\right)\to 5{\mathrm{P}}_{1∕2}\left(F=1\right)$ transition ${}^{87}\mathrm{Rb}$ and transmitted through a rubidium vapor cell as a function of magnetic field $B$. A symmetric resonance doublet of anticorrelated noise is observed for orthogonal polarizations around $B=0$ as a manifestation of ground-state coherence. We also observe sideband noise resonances when the magnetic field produces an atomic Larmor precession at a frequency corresponding to one-half of the analysis frequency. The resonances on the light fluctuations are the consequence of phase to amplitude noise conversion owing to nonlinear coherence effects in the response of the atomic medium to the fluctuating field. A theoretical model (derived from linearized Bloch equations) is presented that reproduces the main qualitative features of the experimental signals under simple assumptions.

We show that a quasiperfect quantum-state transfer between an atomic ensemble and fields in an optical cavity can be achieved in electromagnetically induced transparency (EIT). A squeezed vacuum field state can be mapped onto the long-lived atomic spin associated to the ground-state sublevels of the $\Lambda$-type atoms considered. The EIT on-resonance situation show interesting similarities with the Raman off-resonant configuration. We then show how to transfer the atomic squeezing back to the field exiting the cavity, thus realizing a quantum memory–type operation.

The characteristics of quasi-one-dimensional (1D) high-$n$ Rydberg atoms produced by photoexciting, in a weak dc field, extreme members of the $n=350$ Stark manifold are investigated by studying their ionization when subjected to unidirectional electric field pulses, termed half-cycle pulses (HCP’s), of duration $T_p⪡T_n$ where $T_n$ is the classical electron orbital period, directed both parallel and perpendicular to the atomic axis. The observed differences in the ionization characteristics provide a measure of the anisotropy of the momentum distribution. It is shown that HCP’s applied transverse to the atomic axis provide a particularly sensitive probe of the quasi-1D nature of the state. The experimental data are in good agreement with the results of classical trajectory Monte Carlo simulations.

Absolute cross sections for single and double detachment from ${\mathrm{H}}^{-}$ following electron impact have been measured over a range of collision energies from the thresholds to $170\text{eV}$. The measurements were made using a magnetic storage ring. The ions in the ring were merged with a monoenergetic electron beam and neutral and positively charged fragments were detected. We cover larger energy ranges than in many of the previous experiments, and this is the first time both single and double detachment have been measured simultaneously. This allows us to present accurate ratios between the single and double detachment cross sections. On the basis of these ratio measurements we discuss possible mechanisms leading to double detachment.

We report controlled excitation of ground-state rotational wave packet by pulse-shaping technique. The experiment is conducted in nitrogen $\left({\mathrm{N}}_2\right)$ at room temperature and atmospheric pressure. A femtosecond laser pulse produces rotational coherences in the vibronic ground state of ${\mathrm{N}}_2$ through an impulsive Raman process. The laser pulse is tailored using a spatial light modulator producing spectral phase modulation. Periodic phase steps are applied in order to control the excitation of specific rotational Raman transitions. The outcome is the modification of the relative excitation between odd and even rotational states which allows the control of the symmetry and rephasing period of the wave packet.

We have laser cooled a small cloud of ${}^{40}{\mathrm{Ca}}^{+}$ ions stored in a Penning trap. The large Zeeman splittings that result from the presence of the imposed magnetic field necessitate the use of two cooling lasers tuned to the ${}^2{S}_{1/2}{-}^2{P}_{1/2}$ transition near 397 nm (whereas only a single blue laser frequency is required in an rf trap). The 397 nm radiation is provided by a pair of blue diode lasers operated in extended cavities. Ions can escape from the cooling cycle by falling into a ${}^2{D}_{3/2}$ state. There is also a small probability that ions can be pumped into a ${}^2{D}_{5/2}$ state. The presence of large Zeeman splittings complicates the provision of repumper radiation to empty the D states. We describe two repumping schemes. The first scheme employs five infrared extended cavity diode lasers (ECDL’s). The second scheme employs three infrared ECDL’s, two of which have their injection current modulated to produce sidebands. An upper bound to the temperature of 1 K is inferred from the linewidth of the 397-nm fluorescence for a small cloud of ${}^{40}{\mathrm{Ca}}^{+}$ ions in our Penning trap. This work is part of a program aimed at using atomic ions in a Penning trap for decoherence studies and quantum information processing.

We report on the experimental observation of periodical intensity fluctuations on the output of a fiber soliton ring laser passively mode-locked by using the nonlinear polarization rotation technique. It is found that the appearance of such intensity fluctuations is independent of the orientation of the polarizer in the cavity, but closely related to the pump intensity. We have also numerically simulated the pulse dynamics of the laser. Our numerical simulations confirmed the experimental observations and showed that the soliton pulse nonuniformity is caused by the interaction between the nonlinear polarization rotation and the polarizer in the cavity.

In this paper we propose a setup for the weak measurement of photon arrival time. It is found that the weak values of this arrival time can lie far away from the expectation value, and in principle also in regions forbidden by special relativity. We discuss in brief the implications of these results as well as their reconciliation with the principle of causality. Furthermore, an analysis of the weak arrival times of a pair of photons in a Bell state shows that these weak arrival times are correlated.

We report the observation of laser-induced fluorescence spectra of ${\text{Ba}}^{+*}\text{−}\text{He}$ exciplexes. The experiment is carried out in an environment of cold gaseous helium at a temperature range of $3–30\mathrm{K}$. We have observed the emission spectra of exciplexes by means of excitation of the $6p{}^{2}P_{3∕2}\leftarrow 6s{}^{2}S_{1∕2}$ transition of ${\text{Ba}}^{+}$ ions. It is found that these spectra are redshifted from the $D2$ emission line in the free space and are composed of several peaks. The experimental results are reproduced well by theoretical calculation of the emission spectra for vibrational levels of ${\text{Ba}}^{+*}\text{−}\text{He}$. We also investigate the vibrational dynamics of the $6p{}^2\Pi _{3∕2}$ state of ${\text{Ba}}^{+*}\text{−}\text{He}$, and we have determined the collision-induced vibrational relaxation cross sections of the $6p{}^2\Pi _{3∕2}$ state to be $9.7\pm 1.1{\mathrm{\AA }}^2$ at $15\mathrm{K}$.

Hyperfine quenching rates of the lowest-energy metastable ${}^{3}P_0$ and ${}^{3}P_2$ states of Mg, Ca, Sr, and Yb atoms are computed. The calculations are carried out using ab initio relativistic many-body methods. The computed lifetimes may be useful for designing novel ultraprecise optical clocks and trapping experiments with the ${}^{3}P_2$ fermionic isotopes. The resulting natural widths of the ${}^{3}P_0-{}^{1}S_0$ clock transition are $0.44\text{mHz}$ for ${}^{25}\mathrm{Mg}$, $2.2\text{mHz}$ for ${}^{43}\mathrm{Ca}$, $7.6\text{mHz}$ for ${}^{87}\mathrm{Sr}$, $43.5\text{mHz}$ for ${}^{171}\mathrm{Yb}$, and $38.5\text{mHz}$ for ${}^{173}\mathrm{Yb}$. Compared to the bosonic isotopes, the lifetime of the ${}^{3}P_2$ states in fermionic isotopes is noticeably shortened by the hyperfine quenching but still remains long enough for trapping experiments.

Electric polarizabilities of four even-parity states of atomic barium in the range $\mathrm{35\hspace{0.17em}600}–\mathrm{36\hspace{0.17em}000}{\text{cm}}^{-1}$, excited via two successive $E1$ transitions, are measured using direct spectroscopy. Several states have polarizabilities more than two orders of magnitude larger than might be expected from the known energy levels of Ba, implying the existence of two previously unobserved odd-parity states nearby. These two states are located using Stark-induced excitation, and tentatively identified as $\left(\text{Xe}\right)6s8p{}^{3}P_{0,2}$. The (also unusually high) polarizabilities of these states, as well as that of a third odd-parity state, are reported.

Electron emission from the conduction band of metal surfaces is studied under grazing scattering conditions. We investigate this process making use of the quantum-mechanical (QM) model to represent the electronic interactions within the binary collisional formalism. The QM approach is based on the use of the model potential and allows us to describe the main features of the metal surface. It provides a precise description of both one-electron states and surface induced potential. In this work, the approximation is employed to evaluate electron distributions for $100\text{keV}$ protons impinging grazingly on the $\text{Al}\left(111\right)$ surface. We have found that the realistic representation of the surface included in the QM model introduces substantial changes in the valence emission at low electron energies and intermediate ejection angles. The influence of the surface wake potential on the valence emission probability is also addressed. In order to compare with experiments, we add the contribution coming from atomic inner shells calculated with the field-distorted-wave approximation. Total theoretical results obtained with the QM model are in fairly good agreement with the available experimental data.

We demonstrate that there exist stationary states of Bose-Einstein condensates in an optical lattice that do not satisfy the usual Bloch periodicity condition. Using the discrete model appropriate to the tight-binding limit we determine energy bands for period-doubled states in a one-dimensional lattice. In a complementary approach we calculate the band structure from the Gross-Pitaevskii equation, considering both states of the usual Bloch form and states which have the Bloch form for a period equal to twice that of the optical lattice. We show that the onset of dynamical instability of states of the usual Bloch form coincides with the occurrence of period-doubled states with the same energy. The period-doubled states are shown to be related to periodic trains of solitons.

Injected two-level atoms, prepared and measured in various states, make an effective measurement of the cavity field of a micromaser prior to the injection of the atoms. In contrast to other existing literature on the micromaser, we have used the unconventional retrodictive quantum theory which allows us to calculate, in particular, the phase properties of the field state at an earlier time prior to the interaction with the injected atoms.

The problem of extraction of a single-mode quantum state from a high-$Q$ cavity is studied for the case in which the time of preparation of the quantum state of the cavity mode is short compared with its decay time. The temporal evolution of the quantum state of the field escaping from the cavity is calculated in terms of phase-space functions. A general condition is derived under which the quantum state of the pulse built up outside the cavity is a nearly perfect copy of the quantum state the cavity field was initially prepared in. The results show that unwanted losses prevent the realization of a nearly perfect extraction of nonclassical quantum states from high-$Q$ optical microcavities with presently available technology.

Quantum fluctuation and quantum entanglement of the pump fields reflected from an optical cavity for type-II second-harmonic generation are theoretically analyzed. The correlation spectra of quadrature components between the reflected subharmonic fields are interpreted in terms of pump parameter, intracavity losses, and normalized frequency. High correlation of both amplitude and phase quadratures can be accessed in a triple resonant cavity before the pitchfork bifurcation occurs. The two reflected subharmonic fields are in an entangled state with quantum correlation of phase quadratures and anticorrelation of amplitude quadratures. The proposed system can be exploited as a source for generating entangled states of continuous variables.

We explore classical to quantum transition of correlations by studying the quantum states located just outside of the classically correlated-states-only neighborhood of the maximally mixed state [the largest separable ball (LSB)]. We show that a natural candidate for such states raises the possibility of a layered transition, i.e., an annular region comprising only classical and the classical-like bound entangled states, followed by free or distillable entanglement. Surprisingly, we find the transition to be abrupt for bipartite systems: distillable states emerge arbitrarily close to the LSB. For multipartite systems, white the radius of the LSB remains unknown, we determine the radius of the largest undistillable ball. Our results also provide an upper bound on how noisy shared entangled states can be for executing quantum information processing protocols.

One-body quantum tunneling to continuum is treated via the two-potential approach, dividing the tunneling potential into external and internal parts. We show that corrections to this approach can be minimized by taking the separation radius inside the interval determined by simple expressions. The resulting modified two-potential approach reproduces the resonance’s energy and the width, both for narrow and wide resonances. We also demonstrate that, without losing its accuracy, the two-potential approach can be modified to a form resembling the $R$-matrix theory, yet without any uncertainties related to the choice of the matching radius.

Partial photoionization cross sections (PCSs), ${\sigma }_n$, leading to final ionic states of helium, ${\text{He}}^{+}\left(n\right)$, were measured at BESSY II in the region of doubly excited helium up to the ionization threshold $I_7$ of ${\text{He}}^{+}$. The experiments were performed with a time-of-flight (TOF) electron spectrometer and high photon resolution, $\Delta E\cong 6\text{meV}$. The results of these measurements are a most critical assessment of the decay dynamics of double-excitation resonances and agree well with those of recent eigenchannel $R$-matrix calculations. They also confirm the propensity rules set up for the autoionization of doubly excitated states. The mirroring behavior in the PCSs predicted recently by Liu and Starace is only partially observed. By discussing the formulas given by these authors in a more general context, the specific behavior of the PCSs of helium with respect to mirroring can be understood. The mirroring compensation properties between the “fractional partial cross sections” ${\gamma }_P={\sigma }_P∕{\sigma }_T$ and ${\gamma }_Q={\sigma }_Q∕{\sigma }_T$, with ${\sigma }_T={\sigma }_P+{\sigma }_Q$, are introduced and discussed.