Coherent population trapping (CPT) resonances study in Hanle configuration is reported for different polarizations of the exciting light field, on the $D_2$ line of Cs atoms. While for linear/circular polarization dip/peak in the fluorescence is registered, in case of elliptical polarization, a complex shape resonance is evidenced experimentally, whose profile strongly depends on the ellipticity of polarization. A theoretical model is proposed and developed, which includes the influence on the resonance of polarization ellipticity, transverse magnetic field, and spatial intensity profile of the laser beam. Good agreement is found between the theoretical and experimental results. The reported results allow one to accomplish more profound than in previous research analysis of the CPT resonances behavior pointing out their sensitivity to the light polarization and power as well as to transverse magnetic fields. The presented study is of general importance for the wide application of the coherent resonances in high resolution spectroscopy and precise measurements. The purity of linear/circular polarization of the light needed in different applications can be estimated implementing the proposed model.

We present a theory describing the transients and rise times of the refractive Kerr nonlinearity which is enhanced using electromagnetically induced transparency (EIT). We restrict our analysis to the case of a pulsed signal field with continuous-wave EIT fields, and all fields are well below saturation. These restrictions enable the reduction of an EIT Kerr, four-level, density-matrix equation to a two-level Bloch-vector equation which has a simple and physically intuitive algebraic solution. The physically intuitive picture of a two-level Bloch vector provides insights that are easily generalized to more complex and experimentally realistic models. We consider generalization to the cases of Doppler broadening, many-level EIT systems (we consider the $D1$ line of ${}^{87}\mathrm{Rb}$), and optically thick media. For the case of optically thick media we find that the rise time of the refractive EIT Kerr effect is proportional to the optical thickness. The rise time of the refractive EIT Kerr effect sets important limitations for potential few-photon applications.

A fermion ground state energy functional is set up in terms of particle density, relative pair density, and kinetic energy tensor density. It satisfies a minimum principle if constrained by a complete set of compatibility conditions. A partial set, which thereby results in a lower bound energy under minimization, is obtained from the solution of model systems, as well as a small number of exact sum rules. Prototypical application is made to several one-dimensional spinless noninteracting models. The effectiveness of “atomic” constraints on model “molecules” is observed, as well as the structure of systems with only finitely many bound states.

We have observed severe damage to films of DNA components (thymine, D-ribose, 2-deoxy-D-ribose, and thymidine) induced by $10\text{to}100\mathrm{eV}$ ${\mathrm{He}}^{+}$ ions $(2.5–25\mathrm{eV}∕\mathrm{amu})$. The damage is attributed to the kinetic and potential energies, as well as the chemical reactivity of the ${\mathrm{He}}^{+}$ projectiles. Hyperthermal ${\mathrm{He}}^{+}$ ion impact on these films results in the complete destruction of the molecules via fragmentation, and direct and indirect (secondary fragment) reactive scattering, all of which leads to the desorption of abundant cation and anion fragments. The chemical composition of the fragments is identified, and the fragmentation patterns are compared to those produced by ${\mathrm{Ar}}^{+}$ irradiation. While the lower mass of ${\mathrm{He}}^{+}$ ions causes less efficient desorption of very heavy fragments, several reactive collisions are also observed, including hydrogen abstraction by incident ${\mathrm{He}}^{+}$ from any of the molecules studied to yield desorbing $\mathrm{He}{\mathrm{H}}^{+}$. This process likely occurs via the formation of an intermediate molecular ion ${\left(\mathrm{He}\text{−}\mathrm{H}\text{−}R\right)}^{*+}$, which decays to $\mathrm{He}{\mathrm{H}}^{+}+R^{•}$. Compared to ${\mathrm{Ar}}^{+}$, here a significant $(\times 23)$ enhancement in ${\mathrm{H}}^{+}$ desorption is observed during ${\mathrm{He}}^{+}$ ion irradiation, which likely involves (a) the decay of the intermediate ${\left(\mathrm{He}\text{−}\mathrm{H}\text{−}R\right)}^{*+}$, or desorbing $\mathrm{He}{\mathrm{H}}^{+}$, and (b) Auger or quasiresonant excitations of C, N, or O atom centers (or C-H, N-H, or O-H bonds) by the incident ${\mathrm{He}}^{+}$ ion. The formation of several molecular cations, e.g., ${\mathrm{H}}_3{\mathrm{O}}^{+}$, also requires hydrogen abstraction from its parent or adjacent molecules by initial cation fragments prior to desorption.

We have analyzed the statistical distribution of the fluorescence signal levels in a magneto-optical trap containing a few atoms and observed that it strongly depends on the relative size of the bin time with respect to the trap decay time. We derived analytic expressions for the signal distributions in two limiting cases, long and short bin time limits, and found good agreement with numerical simulations performed regardless of the size of the bin time. We found an optimal size of the bin time for minimizing the probability of indeterminate atom numbers while providing accurate information on the instantaneous number of atoms in the trap. These theoretical results are compared with actual experimental data. We observed super-Poisson counting statistics for the fluorescence from trapped atoms, which might be attributed to uncorrelated motion of trapped atoms in the inhomogeneous magnetic field in the trap.

Our recent measurements on the expansion of a chromium dipolar condensate after release from an optical trapping potential are in good agreement with an exact solution of the hydrodynamic equations for dipolar Bose gases. We report here the theoretical method used to interpret the measurement data as well as more details of the experiment and its analysis. The theory reported here is a tool for the investigation of different dynamical situations in time-dependent harmonic traps.

We derive a class of inequalities, from the uncertainty relations of the su(1,1) and the su(2) algebra in conjunction with partial transposition, that must be satisfied by any separable two-mode states. These inequalities are presented in terms of the su(2) operators $J_x=(a^{†}b+a{b}^{†})∕2$, $J_y=(a^{†}b-a{b}^{†})∕2i$, and the total photon number $⟨N_a+N_b⟩$. They include as special cases the inequality derived by Hillery and Zubairy [Phys. Rev. Lett. 96, 050503 (2006)], and the one by Agarwal and Biswas [New J. Phys. 7, 211 (2005)]. In particular, optimization over the whole inequalities leads to the criterion obtained by Agarwal and Biswas. We show that this optimal criterion can detect entanglement for a broad class of non-Gaussian entangled states, i.e., the su(2) minimum-uncertainty states. Experimental schemes to test the optimal criterion are also discussed, especially the one using linear optical devices and photodetectors.

We investigate the influence the surface description when channeled protons collide grazingly with $\mathrm{LiF}\left(100\right)$ surfaces in the $100–400\mathrm{keV}$ energy range. The projectile is considered to move taking into account the (static and dynamic) potentials with all the ions of the grid. In this model the surface reveals not as an impenetrable isotropic plane but as a complicated percolator strongly dependent on the crystallographic indices, and on the initial conditions.

Coherent population accumulations of multiphoton transitions induced by an ultrashort pulse train in a two-level polar molecule are investigated theoretically by solving the density-matrix equations without invoking any of the standard approximations. It is shown due to the effects of permanent dipole moments, that the population accumulation of multiphoton transitions can be obtained in the polar molecule. Moreover, the population accumulations depend crucially on the relative phase between two sequential pulses, and the period in which the maximum population accumulation occurs is $2\pi ∕N$ in $N$-photon transitions.

We propose a trap scheme for cold alkali-metal atoms with an efficient intensity-gradient induced Sisyphus cooling in a weak standing-wave hollow-beam gravito-optical trap, which is composed of the interference of two well collimated, counterpropagating doughnut hollow beams with an intensity difference and a plug beam. We calculate the intensity distribution of the weak standing-wave hollow-beam field and its intensity gradient one, and find that such an optical dipole trap with an extremely high intensity gradient is desirable to realize an efficient intensity-gradient cooling for alkali-metal atoms in the trap. We also calculate the optical potentials, instantaneous dipole forces and spontaneous emission rates for a three-level dressed atom and study the dynamic process of intensity-gradient cooling of ${}^{87}\mathrm{Rb}$ atoms in the weak standing-wave hollow-beam trap by Monte Carlo simulations. Our study shows that the minimum optical potential at each node in our dipole trap is high enough to trap almost all cold atoms with a temperature of $120\mu \mathrm{K}$ released from a standard magneto-optical trap, and an ultracold ${}^{87}\mathrm{Rb}$ atomic sample with a temperature of $\sim 0.73\mu \mathrm{K}$ can be obtained in the trap. Starting from this stage, an all-optical Bose-Einstein condensation (BEC) could be realized by using the optical-potential evaporative cooling.

In this paper we analyze atom lasers based on the spatial modulation of the scattering length of a Bose-Einstein condensate. We demonstrate, through numerical simulations and approximate analytical methods, the controllable emission of matter-wave bursts and study the dependence of the process on the spatial shape of the scattering length along the axis of emission. We also study the role of an additional modulation of the scattering length in time.

The physics of a Tonks-Girardeau gas confined in an optical lattice in the presence of a local potential is studied. In order to evaluate the single-particle density matrix (SPDM) of the many-body ground state, the Wigner-Jordan transformation is used. The eigenvector with the largest eigenvalue of the SPDM corresponds to the “Bose-Einstein condensate”(BEC) state. We find that the BEC-state density at the position of the local potential decreases, as expected, in the case of a repulsive potential. For an attractive potential, it decreases or increases depending on the strength of the potential. The superfluidity of this system is investigated both numerically and perturbatively. An experimental method for detecting the effect of an impurity in a Tonks-Girardeau gas is discussed.

The temporal confinement of high harmonic generation (HHG) via modulation of the polarization of the fundamental pulse is studied in both temporal and spectral domains. In the temporal domain, a collinear cross-correlation setup using a $40\mathrm{fs}$ IR pump for the HHG and a $9\mathrm{fs}$ IR pulse to probe the generated emission is used to measure the XUV pulse duration. The observed temporal confinement is found to be consistent with theoretical predictions. An increased confinement is observed when a $9\mathrm{fs}$ pulse is used to generate the harmonics. An important spectral broadening, including a continuum background, is also measured. Theoretical calculations show that with $10\mathrm{fs}$ driving pulses, either one or two main attosecond pulses are created depending on the value of the carrier envelope phase.

We develop two variational wave functions of helium which give accurate energy values and satisfy Kato’s cusp conditions adapted to the variational procedure. These wave functions are utilized in calculations for reproducing the electron-helium double-ionization experimental data involving both the small and large momentum transfer. A comparison of the present numerical results for the differential cross sections with experiment indicates a minor role of the cusp conditions.

In a recent paper [S. Bagherinezhad and V. Karimipour, Phys. Rev. A 67, 044302 (2003)], a quantum secret sharing protocol based on reusable GHZ states was proposed. However, in this comment, it is shown that this protocol is insecure because a cheater can gain all the secret bits before sharing, while introducing one data bit error at most in the whole communication, which makes the cheater avoid the detection by the communication parities.

In the preceding Comment [Jian-Zhong Du, Su-Juan Qin, Qiao-Yan Wen, and Fu-Chen Zhu, Phys. Rev. A 74, 016301 (2006)], it has been shown that in a quantum secret sharing protocol proposed in [S. Bagherinezhad and V. Karimipour, Phys. Rev. A 67, 044302 (2003)], one of the receivers can cheat by splitting the entanglement of the carrier and intercepting the secret, without being detected. In this reply we show that a simple modification of the protocol prevents the receivers from this kind of cheating.

Analytical formulas of optimal detunings for efficient and selective excitation of a three-level atomic system derived by Choe et al. [Phys. Rev. A 52, 382 (1995)] predict the values of optimal detunings substantially different from the values mentioned in their paper.

The Comment by G. P. Gupta and B. M. Suri is based on incorrect values of Rabi frequencies, which was caused by a mistake made in the expression of units of Rabi frequencies in the original paper.

The quantized surface mode technique was used to calculate the zero-point energy between two anisotropic parallel plates with nontrivial magnetic properties, one of which is dielectric and the other of which is permeable. The analytical approximate expressions of Casimir force and torque were obtained in the retarded limit. The repulsive Casimir effect can be acquired for some materials with suitable permittivities and permeabilities, which might be measured in a future experiment.

In this paper, we study three specific aspects of entanglement in small spin clusters. We first study the effect of inhomogeneous exchange coupling strengths on the entanglement properties of the $S=\frac{1}{2}$ antiferromagnetic linear chain tetramer compound $\mathrm{Na}\mathrm{Cu}\mathrm{As}{\mathrm{O}}_4$. The entanglement gap temperature $T_E$ is found to have a nonmonotonic dependence on the value of $\alpha$, the exchange coupling inhomogeneity parameter. We next determine the variation of $T_E$ as a function of $S$ for a spin dimer, a trimer, and a tetrahedron. The temperature $T_E$ is found to increase as a function of $S$ but the scaled entanglement gap temperature $t_E$ goes to zero as $S$ becomes large. Last, we study a spin-1 dimer compound to illustrate the quantum complementarity relation. We show that in the experimentally realizable parameter region, magnetization and entanglement plateaus appear simultaneously at low temperatures as a function of the magnetic field. Also, the sharp increase in one quantity as a function of the magnetic field is accompanied by a sharp decrease in the other so that the quantum complementarity relation is not violated.