We use the one-dimensional (1D) Gross-Pitaevskii equation to investigate the dynamical evolution of a dilute repulsive Bose-Einstein condensate (BEC) confined in an elongated static nonharmonic trap and stirred by an oscillating Gaussian obstacle moving at uniform speed in alternate direction. Direct numerical solutions of this equation show that above a critical obstacle velocity, the motion of the obstacle creates gray solitons and phonons. At first, when the velocity of the obstacle increases, the dissipation also increases. But the dissipation reaches a maximal value and then decreases dramatically and vanishes at high obstacle velocities. Our results at low obstacle velocities are similar to those previously obtained experimentally and by simulations in the case of vortice and phonon production in 3D and 2D trapped repulsive BEC’s. But at high obstacle velocities, we show that the quasi-1D trapped repulsive BEC behaves as a quasisuperfluid medium with disappearance of gray soliton and phonon excitations. This extends previous results and provides the main dependence of the phenomenon on the obstacle characteristics.

We present an experimental study of $Z$-scan measurements of the nonlinear response of cold Cs atoms in a magneto-optical trap. Numerical simulations of the $Z$-scan signal accounting for the nonuniform atomic density agree with experimental results at large probe beam detunings. At small probe detunings a spatially varying radiation force modifies the $Z$-scan signal. We also show that the measured scan is sensitive to the atomic polarization distribution.

We give quantum circuits that simulate an arbitrary two-qubit unitary operator up to a global phase. For several quantum gate libraries we prove that gate counts are optimal in the worst and average cases. Our lower and upper bounds compare favorably to previously published results. Temporary storage is not used because it tends to be expensive in physical implementations. For each gate library, the best gate counts can be achieved by a single universal circuit. To compute the gate parameters in universal circuits, we use only closed-form algebraic expressions, and in particular do not rely on matrix exponentials. Our algorithm has been coded in $\mathrm{C}++$.

We demonstrate and evaluate the importance of an intrinsic chirp inherent to attosecond pulse creation accompanying high-order harmonic generation in recently published experimental data by Dinu et al. [Phys. Rev. Lett. 91, 063901 (2003)]. We present an analytical model, from which the atomic origin of the harmonic chirp is clearly understood. Moreover, the behavior of the chirp as a function of experimental parameters such as laser intensity is inferred. The comparison between our model and the experimental data provides us with useful information about the conditions in which the high-order harmonics is generated.

We propose a realizable architecture using one-dimensional transmission line resonators to reach the strong-coupling limit of cavity quantum electrodynamics in superconducting electrical circuits. The vacuum Rabi frequency for the coupling of cavity photons to quantized excitations of an adjacent electrical circuit (qubit) can easily exceed the damping rates of both the cavity and qubit. This architecture is attractive both as a macroscopic analog of atomic physics experiments and for quantum computing and control, since it provides strong inhibition of spontaneous emission, potentially leading to greatly enhanced qubit lifetimes, allows high-fidelity quantum nondemolition measurements of the state of multiple qubits, and has a natural mechanism for entanglement of qubits separated by centimeter distances. In addition it would allow production of microwave photon states of fundamental importance for quantum communication.

We examine one important (and previously overlooked) aspect of well-known crossing diabatic potentials or Landau-Zener $\left(\mathrm{LZ}\right)$ problem. We derive the semiclassical quantization rules for the crossing diabatic potentials with localized initial and localized or delocalized final states, in the intermediate energy region, when all four adiabatic states are coupled and should be taken into account. We found all needed connection matrices and present the following analytical results: (i) in the tunneling region, the splittings of vibrational levels are represented as a product of the splitting in the lower adiabatic potential and the nontrivial function depending on the Massey parameter; (ii) in the overbarrier region, we find specific resonances between the levels in the lower and in the upper adiabatic potentials and, in that condition, independent quantizations rules are not correct; (iii) for the delocalized final states (decay lower adiabatic potential), we describe quasistationary states and calculate the decay rate as a function of the adiabatic coupling; and (iv) for the intermediate energy regions, we calculate the energy level quantization, which can be brought into a compact form by using either adiabatic or diabatic basis set (in contrast to the previous results found in the Landau diabatic basis). Applications of the results may concern the various systems; e.g., molecules undergoing conversion of electronic states, radiationless transitions, or isomerization reactions.

We have measured multiple-ionization yields of $\mathrm{He}$, $\mathrm{Ne}$, $\mathrm{Ar}$, $\mathrm{Kr}$, and $\mathrm{Xe}$ targets by $1.0\mathrm{MeV}∕\mathrm{amu}$ $\mathrm{H}_2{}^{+}$ molecular ions for both the dissociative and nondissociative channels. Except for the case of the breakup of the $\mathrm{H}_2{}^{+}$ into two protons, we have also determined the absolute cross sections for the multiple ionization of the targets. The ratios of multiple to single ionization for the nondissociative channel are similar to those for equivelocity protons, which, however, are consistently smaller than those for the breakup channels, for all charge states and targets. A simple analysis, based on the independent particle model, considering postcollisional time-delayed ionization for the $\mathrm{Ne}$ and $\mathrm{Ar}$ targets, evinces the importance of these mechanisms in the target multiple ionization and of the antiscreening in collisions where the projectile electron undergoes a transition.

${\mathrm{La}}_2$, ${\mathrm{Yb}}_2$, and ${\mathrm{Lu}}_2$ have been studied by use of the density-functional methods B3LYP, BLYP, B3PW91, BHLYP, BP86, B3P86, MPW1PW91, and PBE1PBE. In these density-functional methods, the exchange functional is from either Becke’s three-parameter HF-DFT hybrid exchange functional (B3), pure DFT exchange functional of 1988 (B), a modification of the half-and-half HF/DFT hybrid method (BH), Perdew-Wang 1991 (PW91), or Barone’s modified PW91 (MPW1), while the correlation functional is from either Lee, Yang, and Parr (LYP), Perdew-Wang 1991 (PW91), or Perdew 86 (P86). PBE1PBE is the generalized-gradient-approximation exchange-correlation functional of Perdew, Burke, and Ernzerhof. For ${\mathrm{La}}_2$, the calculated bond distance is in reasonable agreement with the experiment, but the calculated vibrational frequency is underestimated significantly compared with the experiment. Only BP86 and B3P86 have the best performance in reproducing the experimental dissociation energy for ${\mathrm{La}}_2$. For the van der Waals dimer ${\mathrm{Yb}}_2$, three functionals, B3LYP, BLYP, and BHLYP have excellent performance in reproducing the spectroscopic constants compared with both the experiment and previous theoretical studies. For ${\mathrm{Lu}}_2$, the overall performance of the density-functional methods is excellent in predicting the bond distance and vibrational frequency. While for the dissociation energy, PBE1PBE has excellent performance in reproducing the experimental value, followed by MPW1PW91 and B3P86.

A technique to characterize ultrashort x-ray pulses which uses x-ray anomalous transmission in thick crystals (Borrmann effect) is proposed. By exciting coherent optical phonons in a Laue crystal with a fs-laser pulse and measuring the energy of the output diffracted x-ray pulse versus the delay between the two pulses, the temporal structure of the x-ray pulse can be determined with a temporal resolution comparable to the period of the excited vibration. The use of materials with high optical phonon frequencies $(⩾1000{\mathrm{cm}}^{-1})$ would make possible characterization of hard x-ray pulses on a time scale of a few tens of femtoseconds.

We measured the total and partial ion yields of the two chiral amino acids alanine and serine in the gas phase both in the vacuum ultraviolet region and at the $\mathrm{C}\left(1s\right)$ edge using circularly polarized light. We did not detect any circular dichroism asymmetry larger than $1\times {10}^{-3}$. A similar measurement of fixed-in-space amino acids yielded an upper limit of $1\times {10}^{-2}$ for the stereoselective effect of circularly polarized light. The results obtained are relevant for quantitative models of stereoselective photodecomposition of amino acids that try to explain the homochirality of life.

We compare the behavior of absorption and of resonance fluorescence spectra in an extremely thin Rb vapor cell as a function of the ratio of $L∕\lambda$, with $L$ the cell thickness $(L\sim 150–1800\mathrm{nm})$ and $\lambda$ the wavelength of the Rb $D_2$ line $(\lambda =780\mathrm{mn})$. The Dicke-type coherent narrowing [G. Dutier et al., Europhys. Lett. 63, 35 (2003)] is observed only in transmission measurements, in the linear regime, with its typical collapse and revival, which reaches a maximum for $L=(2n+1)\lambda ∕2$ ($n$ integer). It is shown not to appear in fluorescence, whose behavior-amplitude, and spectral width, is more monotonic with $L$. Conversely, at high-intensity, the sub-Doppler saturation effects are shown to be the most visible in transmission around $L=n\lambda$.

Above threshold ionization (ATI) spectra of small metal clusters (e.g., ${\mathrm{Na}}_4$ and $\mathrm{Na}_4{}^{+}$) are calculated numerically using a spherical jellium model and time-dependent density functional theory for two-color (1064 and $532\mathrm{nm}$) ultrashort $\left(25\mathrm{fs}\right)$ laser pulses as a function of phase difference between the two fields. ATI spectra and ionized electron fluxes are obtained in the two opposite directions of the linearly polarized laser fields. The asymmetry, defined as the difference in electron yield, is shown to depend strongly on the carrier-envelope phase of the second-harmonic $\left(2\omega \right)$ field. The ATI spectra allow one to identify the range of kinetic energies of the ionized electrons where the asymmetry mainly occurs. Comparisons are made between calculations with and without self-interaction correction and also with previous exact numerical solutions of the one-electron systems $\mathrm{H}$ and $\mathrm{H}_2{}^{+}$ [A. D. Bandrauk and S. Chelkowski, Phys. Rev. Lett. 84, 3562 (2000)] where such asymmetry effects had first been observed. We find that ATI spectra in the clusters generally have much longer energy plateaus than in previously studied one-electron systems, with cutoffs up to $30–40$ times the ponderomotive energy $U_p$. In high-harmonic generation spectra, on the other hand, no extended plateaus are observed.

We present a Monte Carlo simulation of a typical cavity-QED experiment on the optical Stern-Gerlach effect in terms of the quantum trajectory method. We show that the phenomenon of wave packet splitting may be experimentally observed even in a moderate coupling regime where the atomic and cavity damping rates are comparable to the atom-field coupling strength.

A second-harmonic generation (SHG) is predicted for the Bogoliubov excitations in a two-component Bose-Einstein condensate. It is shown that, because the linear dispersion curve of the excitations displays two branches, the phase-matching condition for the SHG can be fulfilled if the wave vectors and frequencies of fundamental and second-harmonic waves are selected suitably from different branches. The nonlinearly coupled envelope equations for the SHG are derived by using a method of multiple scales. The explicit solutions of these envelope equations are provided and the conversion efficiency of the SHG is also discussed.

We introduce a measure $\mathcal{Q}$ of the “quality” of a quantum which-way detector, which characterizes its intrinsic ability to extract which-way information in an asymmetric two-way interferometer. The “quality” $\mathcal{Q}$ allows one to separate the contribution to the distinguishability of the ways arising from the quantum properties of the detector from the contribution stemming from a priori which-way knowledge available to the experimenter, which can be quantified by a predictability parameter $\mathcal{P}.$ We provide an inequality relating these two sources of which-way information to the value of the fringe visibility displayed by the interferometer. We show that this inequality is an expression of duality, allowing one to trace the loss of coherence to the two reservoirs of which-way information represented by $\mathcal{Q}$ and $\mathcal{P}.$ Finally, we illustrate the formalism with the use of a quantum logic gate: the symmetric quanton-detecton system (SQDS). The SQDS can be regarded as two qubits trying to acquire which-way information about each other. The SQDS will provide an illustrating example of the reciprocal effects induced by duality between system and which-way detector.

When a quantum nonlinear system is linearly coupled to an infinite bath of harmonic oscillators, quantum coherence of the system is lost on a decoherence time scale ${\tau }_D$. Nevertheless, quantum effects for observables may still survive environment-induced decoherence and be observed for times much larger than the decoherence time scale. In particular, we show that the Ehrenfest time, which characterizes a departure of quantum dynamics for observables from the corresponding classical dynamics, can be observed for a quasiclassical nonlinear oscillator for times $\tau ⪢{\tau }_D$. We discuss this observation in relation to recent experiments on quantum nonlinear systems in the quasiclassical region of parameters.

Quantum marking and quantum erasure are discussed for the neutral kaon system. Contrary to other two-level systems, the strangeness and lifetime of a neutral kaon state can be alternatively measured via an “active” or a “passive” procedure. This offers quantum erasure possibilities. In particular, the operation of a quantum eraser in the “delayed choice” mode is clearly illustrated.

The space of quantum Hamiltonians has a natural partition in classes of operators that can be adiabatically deformed into each other. We consider parametric families of Hamiltonians acting on a bipartite quantum state space. When the different Hamiltonians in the family fall in the same adiabatic class, one can manipulate entanglement by moving through energy eigenstates corresponding to different values of the control parameters. We introduce an associated notion of adiabatic entangling power. This novel measure is analyzed for general $d\times d$ quantum systems, and specific two-qubit examples are studied

A complete calculation of the nuclear excitation by electronic transition (NEET) rate of the first excited state of ${}^{235}\mathrm{U}$ in a local thermodynamic equilibrium (LTE) plasma is presented. The microscopic dynamics of the NEET probability are described allowing a clear description of the coupling between the atomic and nuclear transitions for the NEET effect. The atomic properties are estimated in the framework of a relativistic average-atom model. The statistical nature of the electronic transition spectrum is described by the mean of a Gaussian distribution around the average-atom configuration. The analysis of characteristic times occurring in the NEET probability allows one to calculate an equivalent excitation rate in a LTE ${}^{235}\mathrm{U}$ plasma. In the density-temperature plane, the NEET rate is strongly structured, showing the most relevant hydrodynamic conditions for the NEET process. The number of ${}^{235}\mathrm{U}$ nuclei, excited up to the $76.8\text{eV}$ isomeric level in a high-intensity laser shot, has also been estimated.