A general scheme for rotational cooling of diatomic heteronuclear molecules is proposed. It uses a superconducting microwave cavity to enhance the spontaneous decay via Purcell effect. Rotational cooling can be induced by sequentially tuning each rotational transition to cavity resonance, starting from the highest transition level to the lowest one using an electric field. Electrostatic multipoles can be used to provide large confinement volume with essentially homogeneous background electric field.

We present a method to solve the model describing either a Bose-Einstein condensate (BEC) in a Mott-insulator state or a double-well BEC. We show that all the energy eigenvalues and eigenstates for an arbitrary (small or large) total atom number N can be explicitly expressed analytically in terms of a parameter $\lambda$ whose values are determined by the roots of the polynomials of the order of at most $1+\mathrm{int}\mathrm{}(N/2\mathrm{}),$ with $\mathrm{int}\mathrm{}\left(x\right)\mathrm{}$ denoting x’s integer part. We also show that λ’s explicit analytical expressions for $N<~7$ can be readily obtained by a simple MATHEMATICA code. Besides, finding the roots of the polynomials of the order of at most $1+\mathrm{int}\mathrm{}(N/2\mathrm{})\mathrm{}$ to give explicitly all the energy eigenvalues and eigenstates greatly simplifies the corresponding calculations, particularly when the total atom number N is large.

We report on the generation of polarization squeezing of intense, short light pulses using an asymmetric fiber-optic Sagnac interferometer. The Kerr nonlinearity of the fiber is exploited to produce independent amplitude squeezed pulses. The polarization squeezing properties of spatially overlapped amplitude squeezed and coherent states are discussed. The experimental results for a single-amplitude squeezed beam are compared to the case of two phase-matched, spatially overlapped amplitude squeezed pulses. For the latter, noise variances of $-3.4\mathrm{dB}$ below shot noise in the $S_0$ and the $S_1$ and of $-2.8\mathrm{dB}$ in the $S_2$ Stokes parameters were observed, which is comparable to the input squeezing magnitude. Polarization squeezing, that is, squeezing relative to a corresponding polarization minimum uncertainty state, was generated in $S_1.$

We investigate the quantum fluctuations associated with dark-soliton generation in Bose-Einstein condensates. With the phase imprinting procedure treated as a part of the dynamical process, we present numerical solutions of time-dependent quantum depletion. Our results provide evidence of a rapid growth of noncondensate atoms at dark-soliton notches without making assumptions of final quasiparticle states.

A recent experiment demonstrated four-wave mixing of wave packets in a sodium Bose-Einstein condensate [Deng et al., Nature (London) 398, 218 (1999)]. This was followed by a theoretical and numerical treatment of the experiment [Trippenbach et al., Phys. Rev. A 62, 023608 (2000)]. In the experiment, a short time of free expansion of the condensate, after it was released from the magnetic trap, was followed by a set of two Bragg pulses, which created moving wave packets. These wave packets, due to nonlinear interaction and under phase-matching conditions created a new momentum component in a four-wave mixing process. Here we suggest that, instead of exactly matching the frequencies as in the above-mentioned experiments, we admit a small mismatch in energies, and therefore frequencies $\Delta \omega .$ We show that such a small mismatch can compensate for the initial phases built on the condensate during free expansion. A physical explanation is offered. This compensation can be beneficial for the efficiency of the four-wave mixing, in some cases even increasing it by a factor of 2.

The nonlocal properties for a kind of generic N-dimensional bipartite quantum systems are investigated. A complete set of invariants under local unitary transformations is presented. It is shown that two generic density matrices are locally equivalent if and only if all these invariants have equal values in these density matrices.

We rederive the quantum master equation for the decoherence of a massive Brownian particle due to collisions with lighter particles from a thermal environment. Our careful treatment avoids the occurrence of squares of Dirac $\delta$ functions. It leads to a decoherence rate that is smaller by a factor of $2\pi$ compared to previous findings. This result, which is in agreement with recent experiments, is confirmed both by a physical analysis of the problem and by a perturbative calculation in the weak-coupling limit.

The recently introduced detected-jump-correcting quantum codes are capable of stabilizing qubit systems against spontaneous decay processes arising from couplings to statistically independent reservoirs. These embedded quantum codes exploit classical information about which qubit has emitted spontaneously and correspond to an active error-correcting code embedded in a passive error-correcting code. The construction of a family of one-detected-jump-error-correcting quantum codes is shown and the optimal redundancy, encoding, and recovery as well as general properties of detected-jump-error-correcting quantum codes are discussed. By the use of design theory, multiple-jump-error-correcting quantum codes can be constructed. The performance of one-jump-error-correcting quantum codes under nonideal conditions is studied numerically by simulating a quantum memory and Grover’s algorithm.

A primary step in many attempts to ascertain the interaction potential between two colliding quantal systems is to define a “physical” S matrix (or scattering phase shifts) from measured data. We study applications of a controlled random search method of defining such S matrices. This method is model independent and should yield a global minimum form of the S matrix in the sense of a mean square variance in relation to the data. In practice, that is a difficult prospect. In this study, Woods-Saxon potentials, typical of those used in nuclear scattering data analyses, have been used to define the analytic input data for S-matrix analyses. The requirements on that input data with respect to recovery of the known underlying S matrix and the generating interaction potential reveal that a maximum amount of experimentally available data with very high precision is needed to achieve a reliable insight into the nuclear interaction. We found that such sufficient data exceed in both number and precision those given in most published results of actual nuclear scattering experiments. While discussion in this paper is restricted to the elastic scattering of two nuclei, the results have relevance to any other quantum scattering system.

We study the effects of two-photon absorption in the region of the double continuum of helium, with extreme ultraviolet (xuv) laser fields. The nonrelativistic time-dependent Schrödinger equation is solved for the two active electron systems, interacting with strong laser pulses. The dynamic calculations include electronic correlations. The final double continuum states are calculated by treating the electronic term ${1/r}_{12}$ within the zero- and first-order perturbation theory. We calculate the total single and double ionization probabilities and cross sections for photon energies of 45 and 57 eV, as well as the electron energy distributions in the double continuum. The effects of electronic correlations are discussed in the context of ultrashort pulses.

Photodetachment in an ultrastrong laser field in two spatial dimensions is investigated ab initio. A qualitative behavior of the packet for a short-range binding potential is contrasted with that for a soft-core potential, in particular, dynamical effects due to a rescattering of fragments separated from the main packet are demonstrated.

We report high-order harmonic generation (HHG) in rare gases using a femtosecond laser system with a very high repetition rate (100 kHz) and low pulse energy $\left(7\mathrm{}\mu \mathrm{J}\right).\mathrm{}$ To our knowledge, this is the highest repetition rate reported to date for HHG. The tight focusing geometry required to reach sufficiently high intensities implies low efficiency of the process. Harmonics up to the 45th order are nevertheless generated and detected. We show evidence of clear separation and selection of quantum trajectories by moving the gas jet with respect to the focus, in agreement with the theoretical predictions of the semiclassical model of HHG.

Curvature-induced bound-state eigenvalues and eigenfunctions for a particle constrained to move on the surface of a torus are calculated. A limit on the number of bound states that a torus with minor radius a and major radius R can support is obtained. A condition for mapping constrained particle wave functions on the torus into free particle wave functions is established.

Coherent control beyond population control and spectral interferences is demonstrated on the interferences and intensity of the two Autler-Townes (AT) components in the photoelectron spectrum of K atoms, using a sequence of two intense time-delayed femtosecond laser pulses. Photoelectron spectra were taken at various delay times between the two laser pulses and at different laser intensities at a fixed delay time. With respect to the interferences in the AT doublet the role of time delay and laser intensity is interchangeable for $\mathrm{}(n+0.5\mathrm{})\mathrm{}\pi$ excitation. Strong laser fields or the optical phase of the delayed laser pulse allow the quantum mechanical phase of an atomic state to be manipulated in a symmetrical fashion. The observations are discussed in terms of a two-level model coupled to the continuum. For suitable combinations of the laser intensity of the first pulse and the time delay, the second laser pulse leaves the excited state population unchanged.

We present the conditions under which probabilistic error-free discrimination of mixed states is possible, and provide upper and lower bounds on the maximum probability of success for the case of two mixed states. We solve certain special cases exactly, and demonstrate how the problems of state filtering and state comparison can be recast as problems of mixed state unambiguous discrimination.

The Bennett-Brassard cryptographic scheme needs two bases, at least one of them linearly polarized. The problem is that linear polarization, formulated in terms of helicities, is not a relativistically covariant notion: State which is linearly polarized in one reference frame becomes depolarized in another one. We show that a relativistically moving receiver of information should define linear polarization with respect to projection of Pauli-Lubanski’s vector in a principal null direction of the Lorentz transformation which defines the motion, and not with respect to the helicity basis. Such qubits do not depolarize.

High-resolution doubly differential cross section measurements and calculations for electrons elastically scattered through $180°$ from ground-state He- and H-like boron ions are presented covering the entire ${1s2lnl}^{\prime }$ (for ${\mathrm{B}}^{3+})$ and ${2lnl}^{\prime }$ (for ${\mathrm{B}}^{4+})$ Rydberg series populated by resonant excitation. The measurements were performed by zero-degree Auger projectile electron spectroscopy of 4-MeV ${\mathrm{B}}^{3+,4+}$ ions in collisions with ${\mathrm{H}}_2$ targets. R-matrix calculations, particularly sensitive at this large scattering angle to electron correlation, exchange, and interference effects, are found to be in excellent overall agreement within the electron-scattering model.

The mean-square radii of the molecules ${}^4{\mathrm{He}}_3,$ ${}^4{\mathrm{He}}_2{-}^6\mathrm{Li},$ ${}^4{\mathrm{He}}_2{-}^7\mathrm{Li},$ and ${}^4{\mathrm{He}}_2{-}^{23}\mathrm{Na}$ are calculated using a three-body model with contact interactions. They are obtained from a universal scaling function calculated within a renormalized scheme for three particles interacting through pairwise Dirac-$\delta$ interaction. The root-mean-square distance between two atoms of mass $m_A$ in a triatomic molecule are estimated to be of the order of $\mathcal{C}\sqrt{{ħ}^2/\left[m_A{(E}_3-E_2\right)]},$ where $E_2$ is the dimer and $E_3$ is the trimer binding energies, and $\mathcal{C}$ is a constant (varying from $\sim 0.6$ to $\sim 1),$ which depends on the ratio between $E_2$ and $E_3.$ Considering previous estimates for the trimer energies, we also predict the sizes of rubidium and sodium trimers in atomic traps.

Single-, double- and triple-electron-impact detachments from the ${\mathrm{Cl}}^{-}$ ion have been investigated over a collision energy range of 0–95 eV. The experiment was performed at the ion storage ring CRYRING at the Manne Siegbahn Laboratory. The ${\mathrm{Cl}}^{-}$ ions, produced in a sputter ion source, were injected into the ring and accelerated to 2.7 MeV. Thereafter the ions were merged with an electron beam. The electrons served to cool the ion beam. Then they were used as a partner in the electron-ion collisions. The products of the detachment processes, Cl atoms, ${\mathrm{Cl}}^{+},$ and ${\mathrm{Cl}}^{2+}$ ions, were detected after the interaction region with surface-barrier detectors. The shapes of the cross sections for the single, double, and triple detachments show striking similarities.

We report on the experimental realization of an atom optical device that allows scanning of an atomic beam with a controllable diffraction grating for atomic waves. We used a time-modulated evanescent wave field above a glass surface to diffract a continuous beam of metastable neon atoms at grazing incidence. The diffraction angles and efficiencies were controlled by the frequency and form of modulation, respectively. With an optimized shape, obtained from a numerical simulation, we were able to transfer more than 50% of the atoms into the first order beam, which we were able to move over a range of 8 mrad.