We found alternate oscillations in AlGaAs/GaAs single-quantum-well quasistadium laser diodes (QSLDs). Unlike the alternate oscillations in conventional ring lasers, which are explained by interaction between two counterpropagating modes, the alternate oscillations in QSLDs arise from two nearly degenerate cavity modes due to its geometric structure. The lasing signals in QSLDs are directly obtained from the emitted beams which spread over the space without the use of waveguides. We also showed that the alternate oscillation frequencies decrease linearly as the amplitudes of the two different cavity modes increase.

We study a relativistic spin-1/2 fermion subjected to a Dirac oscillator coupling and a constant magnetic field. An interplay between opposed chirality interactions culminates in the appearance of a relativistic quantum phase transition, which can be fully characterized. We obtain analytical expressions for the energy gap, order parameter, and canonical quantum fluctuations across the critical point. Moreover, we also discuss the effect of this phase transition on the statistics of the chiral bosonic ensemble, where its super- or sub-Poissonian nature can be controlled by means of external parameters. Finally, we study the entanglement properties between the degrees of freedom in the relativistic ground state, where an interesting transition between a biseparable and a genuinely tripartite entangled state occurs.

We studied the emission from dense rubidium vapor under 100-fs pulsed laser excitation in the 730–820 nm range. Self-focusing along with a conical emission (CE) was observed for the excitation in the blue wing of $D2$ atomic resonance. Self-defocusing occurred for the red-wing excitation. This is in accordance with the theory of the intensity dependent nonlinear refraction index. In the case of the CE observation, our experimental results are attributed to the self-phase modulation of the laser beam interacting with the near-resonant atomic medium.

Single-photon states (and other non-Gaussian states) are typically studied in the time domain. In contrast, continuous-variable Gaussian states such as squeezed states are typically studied at side-band frequencies. Much of modern optical communication technology is also based on side-band techniques. Here we discuss what it means to produce single-photon states at side-band frequencies and propose techniques for producing and analyzing such states.

In a recent paper [B. Bergues, Z. Ansari, D. Hanstorp, and I. Yu. Kiyan, Phys. Rev. A 75, 063415 (2007)], there is the statement: “Our results unambiguously show that the length gauge is the proper one to use in the frame of the strong-field approximation.” This statement is contested, based on the fact that contrary conclusions from comparisons with experiments have already been demonstrated.

The Comment by Reiss [preceding Comment, H. R. Reiss, Phys. Rev. A 77, 067401 (2008)] is negated. His analysis [H. R. Reiss, Phys. Rev. A 76, 033404 (2007)] of our experimental data on strong-field photodetachment in a circularly polarized laser field [B. Bergues et al., Phys. Rev. Lett. 95, 263002 (2005)] is contested.

We have measured cold titanium-helium collisions that cause transitions between the fine-structure levels of the $\left[3d^{2}4s^2\right]{}^{3}F_J$ electronic ground state of atomic titanium, over a temperature range from 5 to $20\mathrm{K}$. The $\mathrm{Ti}\text{−}\mathrm{He}$ inelastic collision cross section is significantly smaller than cross sections measured for collisions of non-transition-metal atoms with noble gas atoms. Our theoretical calculations of the inelastic cross sections reproduce the magnitude and temperature dependence of the measurements, and attribute the suppression of inelastic collisions to titanium’s “submerged” $d$-shell valence electrons.

We investigate the entanglement properties of thermal states of the harmonic lattice in one, two, and three dimensions. We establish the value of the critical temperature for entanglement between neighboring sites and give physical reasons. Further sites are shown to be entangled only due to boundary effects. Other forms of entanglement are addressed in the second part of the paper by using the energy as witness of entanglement. We close with a comprehensive diagram showing the different phases of entanglement versus complete separability and propose techniques to swap and tune entanglement experimentally.

The hyperfine intervals of the ${}^{133}\mathrm{Cs}$ $7d{}^{2}D_{3∕2}$ manifold are measured using two-photon resonant laser-induced-fluorescence of an effusive cesium beam. A radio-frequency phase modulation technique directly references the relative frequency scale to the ground hyperfine splitting of ${}^{87}\mathrm{Rb}$. The ${}^{133}\mathrm{Cs}$ $7d{}^{2}D_{3∕2}$ hyperfine intervals are used to generate the magnetic dipole coupling constant $A=7.36\pm 0.03\mathrm{MHz}$ and electric quadrupole coupling constant $B=-0.1\pm 0.2\mathrm{MHz}$. The $A$ coupling constant agrees with a previous measurement, but with an improvement in resolution that is sufficient to serve as a benchmark value for testing high-precision theory. The result for the $B$ coupling constant is the first constraint placed on this parameter.

We present measurements of the photoionization cross sections from the $3s$, $3d$, $4s$, $4p$, and $4d$ excited states of lithium isotopes near the first ionization threshold using two dye lasers pumped by a common Nd:YAG (yttrium aluminum garnet) laser in conjunction with an atomic beam–time-of-flight mass spectrometer system. It is observed that the photoionization cross section from the $3d$ and $4d$ excited state is maximum near the ionization threshold and decreases smoothly for the excess energies above the threshold. However, for the $3s$ and $4s$ excited states, the photoionization cross section is lower at the threshold, increases to a maximum value, and then decreases monotonically for the excess energies. It is also observed that a drop off in the cross section of the $nd$ states is more hydrogenic than that of the $np$ and $ns$ excited states.

We present an accurate computation of the $g$ factors of the hyperfine states of the hydrogen molecular ion $\text{H}_2{}^{+}$. The results are in good agreement with previous experiments, and can be tested further by rf spectroscopy. Their implication for high-precision two-photon vibrational spectroscopy of $\text{H}_2{}^{+}$ is also discussed. It is found that the most intense hyperfine components of two-photon lines benefit from a very small Zeeman splitting.

Doubly resonant multiphoton ionization of PbF has been achieved via the $X_1\to A$ and $A\to D$ transitions. Excitation of the $A$ to the $D$ state by narrow-bandwidth laser radiation is found to have a cross section of ${\sigma }_D=100\pm 30\text{Mb}$. The ionization potential is found to be 7.55(1) eV, in agreement with our previous result. The lifetime of the $D$ state is found to be $250\pm 150\text{ps}$ and the ionization cross section is found to be ${\sigma }_{+}=90\pm 60\text{Mb}$. These characteristics allow for efficient state-selective ionization of the PbF molecule.

In this paper a class of model suitable for application to collision-sequence interference is studied. In these models it is assumed that the intervals between collisions are constant rather than exponentially distributed, as would be true if the collision times formed a Poisson process. The model may be two dimensional or three dimensional. Velocities are assumed to be completely randomized in each collision. The distribution of velocities is assumed to be Gaussian, though use is not always made of that fact. As applied to vector collisional interference the models allow the evaluation of the effects of windowing, which is of importance for $\mathcal{N}$-body simulation of more physically accurate models. They also lead to estimation of the effects of infilling of the interference dip following from deviations of the induced dipole moment from the intermolecular force. As applied to scalar collisional interference the models show the existence of a hitherto unknown (albeit weak) correlation between immediately successive collisions. An extension to the models, in which the magnitude of the induced dipole moment is equal to an arbitrary power or sum of powers of the intermolecular force, allows estimates of the infilling of the interference dip by the disproportionality of the induced dipole moment and force. One particular such model leads to the most realistic estimate for the infilling yet obtained.

The double ionization of helium by electron impact for $106\mathrm{eV}$ incident energy was studied in a kinematically complete experiment by using a reaction microscope. The pattern of the angular correlation of the three emitted electrons was analyzed by selecting different values of the recoil ion longitudinal momentum. The Wannier predicted geometry appears when the recoil ion carries the full initial projectile momentum. It was found that at this low impact energy, the outgoing electrons still remember the initial-state collision information.

We present the computation of two-photon transition spectra between rovibrational states of the $\text{H}_2{}^{+}$ molecular ion, including the effects of hyperfine structure and excitation polarization. The reduced two-photon matrix elements are obtained by means of a variational method. We discuss the implications of our results for high-resolution spectroscopy of $\text{H}_2{}^{+}$.

The photon emission spectrum of the hydrogen atom in an intense high-frequency laser pulse is simulated to show that regular fine structures appear in the two sides of both the odd and even order harmonics. The splitting of the fine structures around the normal harmonic line are determined by the energy differences of the eigenstates of the time averaged Kramers-Henneberger potential with the same parity. The lines around the even order harmonic positions are produced by the hyper-Raman transitions between the dressed atomic states with different parities. The hyper-Raman lines are predicted as long as stabilization occurs and are not so sensitive to the initial state of the atom as those appearing with the low-frequency and less strong laser field. The hyper-Raman lines can be strongly reduced with longer turn-on and turn-off times.

We introduce a new class of sine-Gordon models, for which the interaction term is present in a region different from the domain over which the quadratic part is defined. We develop a nonperturbative approach for calculating partition functions of such models, which relies on mapping them to statistical properties of random surfaces. As a specific application of our method, we consider the problem of calculating the amplitude of interference fringes in experiments with two independent low dimensional Bose gases. We calculate full distribution functions of interference amplitude for one-dimensional and two-dimensional gases with nonzero temperatures.

We investigate the quantum noise in phase quadratures of resonance fluorescence from a two-level atom driven by a trichromatic exciting field. It is shown that the noise spectra are crucially dependent on the sum of relative phases of the sideband components compared to the central component although the sideband exciting components are much weaker than the central component. When we tune the exciting sidebands on two-photon resonance with the Mollow sideband transitions and set the phase sum to $\pi$, sideband squeezing in the in-phase quadrature remains almost the same as in the monochromatic case. Once the phase sum is set to zero, the squeezing is destroyed. The responsible mechanism is explained in terms of two-photon emission processes induced by the trichromatic components and the interference between these processes.

We investigate the existence and linear stability of coupled vortex solitons supported by cascaded four-wave mixing in a Raman active medium excited away from the resonance. We present a detailed analysis for the two- and three-component vortex solitons and demonstrate the formation of stable and unstable vortex solitons, and associated spatiotemporal helical beams, under the conditions of the simultaneous frequency and vortex comb generation.

We consider squeezing of one component of the collective spin vector of an atomic ensemble inside an optical cavity. The atoms interact with a cavity mode, and the squeezing is obtained by probing the state of the light field that is transmitted through the cavity. Starting from the stochastic master equation, we derive the time evolution of the state of the atoms and the cavity field, and we compute expectation values and variances of the atomic spin components and the quadratures of the cavity mode. The performance of the setup is compared to spin squeezing of atoms by probing of a light field transmitted only once through the sample.