We present atom chip traps and guides created by a combination of two current-carrying wires and a bias field pointing perpendicular to the chip surface. These elements can be arranged in any orientation on the chip surface. We study loading schemes for the traps and present a detailed study of the guiding of thermal atomic clouds in an omnidirectional matter waveguide along a $25\text{−}\mathrm{mm}$-long curved path at various atom-surface distances $(35–450\mu \mathrm{m})$. An extension of the scheme for the guiding of Bose-Einstein condensates is outlined. Such a concept enables utilizing the full two-dimensional surface of the chip.

In this paper we investigate the resonance fluorescence, the squeezing, and the absorption spectra of a laser-driven four-level atom consisting of three closely spaced upper levels decaying to a common lower level. The three upper levels are coupled by the same vacuum modes to the lower level leading to spontaneously generated coherence effects. High population inversion and extremely narrow emission lines are obtained with moderate Rabi frequencies, which are a direct consequence of decay-induced interferences. The fluorescent field is shown to exhibit two-mode squeezing in the in-phase quadrature. Squeezing in both quadratures simultaneously at different frequencies is greatly enhanced when quantum interference is accounted for. We also examine the absorption spectrum of a weak field and demonstrate that quantum interference can induce two prominent and nearly transparent holes where the slope of the refractive index is very steep. This special situation could allow the simultaneous propagation of two weak pulses with different frequencies, which could be feasibly exploited towards the realization of the entanglement of two photons.

A tunable scheme for slowing down and stopping light using the backward frequency conversion in the quasi-phase-matched waveguides is proposed. It is shown that delay time ranging from a nanosecond to hundreds of microseconds can be obtained in few-centimeter-long GaAs-based structures with up to ten GHz bandwidths at moderate (few W) peak powers of coupling light. The proposed scheme also allows one to continuously change the frequency of the signal.

The polarization characteristics of the signal wave produced in Rb vapor by difference-frequency, parametric four-wave mixing (FWM) has been investigated for either ultrafast $(\sim 150\mathrm{fs})$ or nanosecond time-scale excitation of the $5s\to \to 5d$, $7s$ two photon transitions. The electronic configurations of the $5d{}^{2}D_{5∕2}$ and $7s{}^{2}S_{1∕2}$ states of Rb, as well as their energy separation $(\sim 608{\mathrm{cm}}^{-1})$, offers the opportunity to examine separately the resonantly enhanced $5s\to \to 7s$, $5d\to 6p\to 5s$ FWM pathways on the nanosecond time scale and then to drive both channels simultaneously with an ultrafast pulse of sufficient spectral width. As expected, dye laser $(\sim 10\mathrm{ns})$ excitation of the $5s\to \to 5d$ $(J=5∕2)$ transition produces a signal wave $({\lambda }_s\sim 420\mathrm{nm})$ having the same ellipticity as the driving optical field. Two photon excitation of Rb $\left(7s\right)$ on the same time scale, however, generates an elliptically polarized signal when the pump is linearly polarized $(\epsilon =1)$, a result attributed to $7s\to 6p$, $5p$ amplified spontaneous emission at $\sim 4\mu \mathrm{m}$ and $\sim 741\mathrm{nm}$, respectively. Simultaneous excitation of the $5s\to \to 7s$, $5d$ transitions with $\sim 150\mathrm{fs}$ pulses centered at $\sim 770\mathrm{nm}$ yields polarization characteristics that can be approximated as a superposition of those for the individual transitions, thus displaying weak coupling between the two FWM channels. Also, the influence of molecular contributions to the FWM signal is observed for Rb number densities above $\sim 5\times {10}^{14}{\mathrm{cm}}^{-3}$.

A method for obtaining the WKB wave function describing the particle tunneling outside of a two-dimensional potential well is suggested. The Cartesian coordinates $(x,y)$ are chosen in such a way that the $x$ axis has the direction of the probability flux at large distances from the well. The WKB wave function is then obtained by simultaneous expansion of the wave function in the coordinate $y$ and the parameter determining the curvature of the escape path. It is argued, both physically and mathematically, that these two expansions are mutually consistent. It is shown that the method provides systematic approximation to the outgoing probability flux. Both the technical and conceptual advantages of this approach in comparison with the usual approach based on the solution of classical equations of motion are pointed out. The method is applied to the problem of the coupled anharmonic oscillators and verified through the dispersion relations.

The local field correction to the spontanous decay rate of an impurity source atom embedded in a disordered dielectric is calculated to second order in the dielectric density. The result is found to differ from predictions associated with both “virtual” and “real” cavity models of this decay process. However, if the contributions from two dielectric atoms at the same position are included, the virtual cavity result is reproduced.

We calculate the entanglement of formation and the entanglement of distillation for arbitrary mixtures of the zero spin states on an arbitrary-dimensional bipartite Hilbert space. Such states are relevant to quantum black-holes and to decoherence-free subspaces based communication. The two measures of entanglement are equal and scale logarithmically with the system size. We discuss its relation to the black-hole entropy law. Moreover, these states are locally distinguishable but not locally orthogonal, thus violating a conjecture that the entanglement measures coincide only on locally orthogonal states. We propose a slightly weaker form of this conjecture. Finally, we generalize our entanglement analysis to any unitary group.

A recently developed single-center model of double photoionization (DPI) of the ${\mathrm{H}}_2$ molecule [Kheifets, Phys. Rev. A 71, 022704 (2005)] has been extended to represent the DPI process at unequal energy sharing. The model is applied to describe the shape of the fully-differential cross-section (FDCS) of a randomly oriented hydrogen molecule in the isotopic form of ${\mathrm{D}}_2$ at the kinematics of recent experiments. Comparison with analogous FDCS for the He atom helps to elucidate the molecular effects.

We solve the time-dependent Schrödinger equation for an ion-molecule collision using a lattice approach. This method carries over naturally from similar lattice treatments of ion-atom collisions, and is free from the multicenter problems that make extensions of other ion-atom methods difficult.

Experiments of Zweiback et al. [Phys. Rev. Lett. 84, 2634 (2000)] on the interaction of intense femtosecond laser pulses with a dense molecular beam of large deuterium clusters have shown that these clusters can lose most of their electrons and explode, in a process known as Coulomb explosion. The collisions between the fast deuterium (D) nuclei give rise to D-D fusion. This has motivated us to carry out computer simulations based on the time-dependent density-functional theory in order to understand the ultrafast processes occurring under these high excitations. In particular we have studied the laser irradiation of the singly charged cluster $\mathrm{D}_{13}{}^{+}$. The simulations show the occurrence of two different cluster fragmentation behaviors, depending on the intensity of the laser pulse: For not too large intensities, the cluster becomes disassembled in a slow way, whereas for large laser intensities substantial ionization takes place and a violent explosion occurs due to the electrostatic repulsion between the nuclei following the loss of the electrons by the cluster. The fast fragmentation mode fits well into the idea of the Coulomb explosion.

Backscattered signal of coherent anti-Stokes Raman spectroscopy can be an extremely useful tool for remote identification of airborne particles, provided the signal is sufficiently large. We formulate a semiclassical theory of nonlinear scattering to estimate the number of detectable photons from a bacterial spore at a distance. For the first time, the theory incorporates enhanced quantum coherence via femtosecond pulses and a nonlinear process into the classical scattering problem. Our result shows a large backscattered signal in the far field, using typical parameters of an anthrax spore with maximally prepared vibrational coherence. Using train pulses of 1 kHz of repetition rate each with energy of 10 mJ, we estimate that about ${10}^7$ photons can be detected by a 1 m diameter detector placed 1 km away from the spore in the backward scattering direction. The result shows the feasibility of developing a real time remote detection of hazardous microparticles in the atmosphere, particularly biopathogenic spores.

A theoretical investigation on the coherent control of optical transient four-wave mixing interactions in two-level systems with two intense few-cycle propagating laser pulses of central angular frequencies $\omega$ and $3\omega$ is reported. By numerically solving the full Maxwell-Bloch equations beyond the slowly varying envelope and rotating-wave approximations in the time domain, the nonlinear coupling to the optical field at frequency $5\omega$ is found to depend critically on the initial relative phase $\varphi$ of the propagating pulses: the coupling is enhanced when the pulses interfere constructively in the center $(\varphi =0)$, while it is nearly suppressed when they are out of phase $(\varphi =\pi )$.

The coupling-constant dependence is derived in time-dependent current-density-functional theory. The scaling relation can be used to check approximate functionals and in conjunction with the adiabatic connection formula to obtain the ground-state energy from the exchange-correlation kernel. The result for the uniform gas using the Vignale-Kohn approximation is deduced.

We calculate the bound-state energy spectrum of the Dirac equation in a Schwarzschild black-hole background using a minimax variational method. Our method extends that of Talman to the case of non-Hermitian interactions, such as a black hole. The trial function is expressed in terms of a basis set that takes into account both the Hermitian limit of the interaction in the nonrelativistic approximation, and the general behavior of the solutions at the origin, the horizon, and infinity. Using this trial function an approximation to the full complex-energy bound-state spectrum is computed. We study the behavior of the method as the coupling constant of the interaction is increased, which increases both the relativistic effects and the size of the non-Hermitian part of the interaction. Finally we confirm that the method follows the expected Hylleraas-Undheim behavior.

We discuss the generation and evolution of entangled light in a correlated spontaneous emission laser. The master equation for the two-mode field in a cavity is derived and solved analytically. The time-dependent characteristic function in the Wigner representation for the two-mode field is obtained. It shows that the two-mode field in the cavity evolves in a two-mode Gaussian state. The entanglement degree of the two-mode field in the cavity increases initially, then decreases, and finally vanishes as the field evolves from an initial vacuum. The period of the entanglement is extended as the intensity of the driving field is increased. It is found that the entanglement still exists even when the two-mode squeezing disappears. During the entanglement period, the intensity of the field is amplified. The entanglement for the initial field being a two-mode squeezed vacuum and the entanglement of the output field are also discussed.

We propose experimental schemes to implement ancilla-free $1\to 3$ optimal phase covariant quantum cloning machines for $x\text{−}y$ and $x\text{−}z$ equatorial qubits by interfering a polarized photon, which we wish to clone, with different light resources at a six-port symmetric beam splitter. The scheme requires linear optical elements and three-photon coincidence detection, and is feasible with current experimental technology.

The technique of stimulated Raman adiabatic passage (STIRAP) is used to excite laser-cooled rubidium atoms from the ${}^{85}\mathrm{Rb}5S_{1∕2}$ ground state to the $44D_{5∕2}$ Rydberg state through the $5P_{3∕2}$ state. The utilized double-STIRAP scheme allows for an accurate determination of the absolute excitation efficiency. Experimental data are compared with results of a detailed theoretical model, and good agreement is found. It is concluded that at the center of the excitation region an excitation efficiency of 70% is achieved.

We study the phenomenon of electromagnetically induced transparency (EIT) of ${}^{87}\mathrm{Rb}$ vapor at the temperature of $325\mathrm{K}$ in a magnetic field. Two linearly polarized orthogonal laser fields act on two dipole-allowed transitions of the $D1$ line of ${}^{87}\mathrm{Rb}$ in the $\Lambda$ configuration, respectively. In the absence of magnetic fields, we observe a wide EIT window with the contrast of about 66% while when the magnetic field is applied, the wide EIT window is split into three or four narrower subwindows with contrasts of 32% or 16% due to the lifting of magnetic sublevels’ degeneracy. The number of EIT subwindows depends on the magnetic field orientation. Our theoretical simulations and analysis are in good agreement with the experimental results.

We propose an alternative and simple method to create states of the quantized radiation field with controlled holes in their photon-number distribution. The scheme relies on resonant interaction of a cavity field with two-level Rydberg atoms plus selective atomic detection.

We perform ab initio calculations of isotope shifts for isotopes of cesium (from $A=123$ to $A=137$) and francium (from $A=207$ to $A=228$). These calculations start from the relativistic Hartree-Fock method and make use of several techniques to include correlations. The field (volume) isotope shift is calculated by means of an all-order correlation potential method and within the singles-doubles–partial-triples linearized coupled-cluster approach. Many-body perturbation theory in two different formulations is used to calculate the specific mass shift. We discuss the strong points and shortcomings of the different approaches and implications for parity nonconservation in atoms. Changes in nuclear charge radii are found by comparing the present calculations with experiment.