Current-spin-density-functional theory (CSDFT) provides a framework to describe interacting many-electron systems in a magnetic field which couples to both spin and orbital degrees of freedom. Unlike in the usual (spin-)density-functional theory, approximations to the exchange-correlation energy based on the model of the uniform electron gas face problems in practical applications. In this work, explicitly orbital-dependent functionals are used and a generalization of the optimized effective potential method to the CSDFT framework is presented. A simplifying approximation to the resulting integral equations for the exchange-correlation potentials is suggested. A detailed analysis of these equations is carried out for the case of open-shell atoms and numerical results are given using the exact-exchange energy functional. For zero external magnetic field, a small systematic lowering of the total energy for current-carrying states is observed due to the inclusion of the current in the Kohn-Sham scheme. For states without current, CSDFT results coincide with those of spin-density-functional theory.

When an electron in a localized orbital approaches a continuum, resonant charge transfer can occur. For instance, when a beam of ions is scattered from a metal surface, neutralization can take place through the transfer of an electron either from ion to metal—in the case of a negative ion—or from metal to ion—in the case of a positive ion. Similarly, a neutral atom may be ionized by removing an electron from the metal surface. In this paper, we introduce the wide-band diabatic dynamics (WBDD) method for simulating the quantum dynamics of such systems by decoupling the equations of motion for the ionic and neutral diabats. We show numerically that our approximation accurately describes the quantum nuclear dynamics near the metal surface. Although we treat the case of ion neutralization, our method is general, and can be applied to any quantum state interacting with a continuum via a position-dependent interaction, provided that the wide-band approximation holds.

We present an experimental study of the spectra produced by optical–radio-frequency double resonance in which resonant linearly polarized laser light is used in the optical pumping and detection processes. We show that the experimental spectra obtained for cesium are in excellent agreement with a very general theoretical model developed in our group [Weis, Bison, and Pazgalev, Phys. Rev. A 74, 033401 (2006)] and we investigate the limitations of this model. Finally, the results are discussed in view of their use in the study of relaxation processes in aligned alkali-metal vapors.

The evolving field of nanofabrication demands that more precise fabrication and evaluation tools be developed. We describe a method for creating a high quality focused ion beam with enhanced capabilities using an ion source based on laser-cooled neutral atoms in a magneto-optical trap. This technique will improve resolution and brightness beyond the current state of the art, can be used with the full range of atomic species that can be laser cooled and trapped, and will allow unprecedented control over the ion emission, allowing, for example, the production of single ions “on demand.” We give estimates for the emittance and present a realistic ray tracing analysis of a basic focusing system demonstrating the feasibility of focusing the beam to a spot size of less than $10\mathrm{nm}$.

Thermodynamics of a three-level maser was studied in the pioneering work of Scovil and Schulz-DuBois [Phys. Rev. Lett. 2, 262 (1959)]. In this work we consider the same three-level model, but treat both the matter and the light quantum mechanically. Specifically, we analyze an extended (three-level) dissipative (ED) Jaynes-Cummings model (JCM) within the framework of a quantum heat engine, using formulas for heat flux and power in bipartite systems introduced in our previous work [E. Boukobza and D. J. Tannor Phys. Rev. A 74, 063823 (2006)] Amplification of the selected cavity mode occurs even in this simple model, as seen by a positive steady state power. However, initial field coherence is lost, as seen by the decaying off-diagonal field density matrix elements, and by the Husimi-Kano $Q$ function. We show that after an initial transient time the field’s entropy rises linearly during the operation of the engine, which we attribute to the dissipative nature of the evolution and not to matter-field entanglement. We show that the second law of thermodynamics is satisfied in two formulations (Clausius, Carnot) and that the efficiency of the ED JCM heat engine agrees with that defined intuitively by Scovil and Schulz-DuBois. Finally, we compare the steady state heat flux and power of the fully quantum model with the semiclassical counterpart of the ED JCM, and derive the engine efficiency formula of Scovil and Schulz-DuBois analytically from fundamental thermodynamic fluxes.

Heat and work for quantum systems governed by dissipative master equations with a time-dependent driving field were introduced in the pioneering work of Alicki [J. Phys. A 12, L103 (1979)]. Alicki’s work was in the Schrödinger picture; here we extend these definitions to the Heisenberg and interaction pictures. We show that, in order to avoid consistency problems, the full time derivatives in the definitions for heat flux and power (work flux) should be replaced by partial time derivatives. We also present an alternative approach to the partitioning of the energy flux which differs from that of Alicki in that the instantaneous interaction energy with the external field is not included directly. We then proceed to generalize Alicki’s definition of power by replacing the original system and its external driving field with a larger, bipartite system, governed by a time-independent Hamiltonian. Using the definition of heat flux and the generalized definition of power, we derive the first law of thermodynamics in differential form, for both the full bipartite system and the partially traced subsystems. Although the second law (Clausius formulation) is satisfied for the full bipartite system, we find that in general there is no rigorous formulation of the second law for the partially traced subsystem unless certain additional requirements are met. Once these requirements are satisfied, however, both the Carnot and the Clausius formulations of the second law are satisfied. We illustrate this thermodynamic analysis on both the simple Jaynes-Cummings model and an extended dissipative Jaynes-Cummings model, which is a model for a quantum amplifier.

An experimental study of high-order harmonic generation in In, InSb, InP, and InGaP plasmas using femtosecond laser radiation with variable chirp is presented. Intensity enhancement of the 13th and 21st harmonics compared to the neighboring harmonics by a factor of 200 and 10, respectively, is observed. It is shown that the harmonic spectrum from indium-containing plasma plumes can be considerably modified by controlling the chirp of the driving laser pulse.

In recent years it has become apparent that constraints on possible quantum operations, such as those constraints imposed by superselection rules (SSRs), have a profound effect on quantum information theoretic concepts like bipartite entanglement. This paper concentrates on a particular example: the constraint that applies when the parties (Alice and Bob) cannot distinguish among certain quantum objects they have. This arises naturally in the context of ensemble quantum information processing such as in liquid NMR. We discuss how a SSR for the symmetric group can be applied, and show how the extractable entanglement can be calculated analytically in certain cases, with a maximum bipartite entanglement in an ensemble of $N$ Bell-state pairs scaling as $\log \left(N\right)$ as $N\to \infty$. We discuss the apparent disparity with the asymptotic $(N\to \infty )$ recovery of unconstrained entanglement for other sorts of superselection rules, and show that the disparity disappears when the correct notion of applying the symmetric group SSR to multiple copies is used. Next we discuss reference frames in the context of this SSR, showing the relation to the work of von Korff and Kempe [Phys. Rev. Lett. 93, 260502 (2004)]. The action of a reference frame can be regarded as the analog of activation in mixed-state entanglement. We also discuss the analog of distillation: there exist states such that one copy can act as an imperfect reference frame for another copy. Finally we present an example of a stronger operational constraint, that operations must be noncollective as well as symmetric. Even under this stronger constraint we, nevertheless, show that Bell nonlocality (and hence entanglement) can be demonstrated for an ensemble of $N$ Bell-state pairs no matter how large $N$ is. This last work is a generalization of that of Mermin [Phys. Rev. D 22, 356 (1980)].

How entangled is a randomly chosen bipartite stabilizer state? We show that if the number of qubits each party holds is large, the state will be close to maximally entangled with probability exponentially close to 1. We provide a similar tight characterization of the entanglement present in the maximally mixed state of a randomly chosen stabilizer code. Finally, we show that typically very few Greenberger-Horne-Zeilinger states can be extracted from a random multipartite stabilizer state via local unitary operations. Our main tool is a concentration inequality which bounds deviations from the mean of random variables which are naturally defined on the Clifford group.

Motivated by a recent experiment by Zelevinsky et al. [Phys. Rev. Lett. 96, 203201 (2006)], we present the theory for photoassociation and optical Feshbach resonances of atoms confined in a tight one-dimensional (1D) or two-dimensional (2D) optical lattice. In the case of an alkaline-earth-metal intercombination resonance, the narrow natural width of the line makes it possible to observe clear manifestations of the dimensionality, as well as some sensitivity to the scattering length of the atoms. Among possible applications, a 2D lattice may be used to increase the spectroscopic resolution by about one order of magnitude. Furthermore, a 1D lattice induces a shift that provides an alternative way of determining the strength of a resonance by spectroscopic measurements.

Collision-induced light emission during the interaction of an alkali-metal atom and a noble-gas atom is treated within a first-principles, or direct, dynamics approach that calculates a time-dependent electric dipole for the whole system, and spectral emission cross sections from its Fourier transform. These cross sections are very sensitive to excited diatomic potentials and a source of information on their shape. The coupling between electronic transitions and nuclear motions is treated with atomic pseudopotentials and an electronic density matrix coupled to trajectories for the nuclei. A recently implemented pseudopotential parametrization scheme is used here for the ground and excited states of the LiHe system, and to calculate state-to-state dipole moments. To verify the accuracy of our new parameters, we recalculate the integral cross sections for the LiHe system in the keV energy regime and obtain agreement with other results from theory and experiment. We further present results for the emission spectrum from $10\mathrm{keV}$ $\mathrm{Li}\left(2s\right)+\mathrm{He}$ collisions, and compare them to experimental values available in the region of light emitted at $300–900\mathrm{nm}$.

The multiphoton resonant excitation of three-level atoms by the two laser fields of different frequencies is investigated. The time evolution of the system and analytical solutions expressing Rabi oscillations of the probability amplitudes at the two-color multiphoton resonant excitation are found using a nonperturbative resonant approach. The specific examples for experimental implementation of two-color multiphoton resonant excitation of hydrogen atoms are considered.

The strong-coupling limit of molecule formation in an atomic Bose-Einstein condensate via two-mode one-color photoassociation or sweep across a Feshbach resonance is examined using a basic nonlinear time-dependent two-state model. For the general class of term-crossing models with constant coupling, a common strategy for attacking the problem is developed based on the reduction of the initial system of semiclassical equations for atom-molecule amplitudes to a third-order nonlinear differential equation for the molecular state probability. This equation provides deriving exact solution for a class of periodic level-crossing models. These models reveal much in common with the Rabi problem. Discussing the strong-coupling limit for the general case of variable detuning, the equation is further truncated to a limit first-order nonlinear equation. Using this equation, the strong nonlinearity regime for the first Nikitin exponential-crossing model is analyzed and accurate asymptotic expressions for the nonlinear transition probability to the molecular state are derived. It is shown that, because of a finite final detuning involved, this model displays essential deviations from the Landau-Zener behavior. In particular, it is shown that in the limit of strong coupling the final conversion probability tends to $1∕6$. Thus, in this case the strong interaction limit is not optimal for molecule formation. We have found that if optimal field intensity is applied the molecular probability is increased up to $1∕4$ (i.e., the half of the initial atomic population).

We calculate the structure of individual vortices in rotating Bose-Einstein condensates in a transverse harmonic trap. Making a Wigner-Seitz approximation for the unit cell of the vortex lattice, we derive the Gross-Pitaevskii equation for the condensate wave function in each cell of the lattice, including effects of varying coarse grained density. We calculate the Abrikosov parameter, the fractional core area, and the energy of individual cells.

We demonstrate a scheme for the Fourier synthesis of periodic optical potentials with asymmetric unit cells for atoms. In a proof of principle experiment, an atomic Bose-Einstein condensate is exposed to either symmetric or sawtooth-like asymmetric potentials by superimposing a conventional standing wave potential of $\lambda ∕2$ spatial periodicity with a fourth-order lattice potential of $\lambda ∕4$ periodicity. The high periodicity lattice is realized using dispersive properties of multiphoton Raman transitions. Future applications of the demonstrated scheme could range from the search for novel quantum phases in unconventionally shaped lattice potentials up to dissipationless atomic quantum ratchets.

Bose-condensed gases are considered with an effective interaction strength varying in the whole range of the values between zero and infinity. The consideration is based on the usage of a representative statistical ensemble for Bose systems with broken global gauge symmetry. Practical calculations are illustrated for a uniform Bose gas at zero temperature, employing a self-consistent mean-field theory, which is both conserving and gapless.

We demonstrate in experiment that the simultaneous use of two laser fields, a saturating and a coupling field, allows us to observe three or four coherent hole burnings with controllable widths, depths, and positions in a single Doppler absorption profile. Appropriate theoretical simulations and analysis show that these correlated coherent hole burnings result from the combination of strong saturating excitation and dynamically induced quantum coherence.

Higher-order harmonic generation from strong laser-atom interaction in the multicycle regime is investigated using the Lewenstein model. While the peak intensity of the driving laser is oversaturated, the atom will be ionized completely during a few half optical cycles. The harmonic spectrum then reveals a continuous multiplateau structure in the cutoff region because of the ground state depletion. Each subplateau can be superposed to generate single attosecond pulse. Since the intensity of high-order harmonics from ion is comparable to that from atom if the peak intensity is super-intense, appropriate subplateau should be selected for single attosecond pulse generation. It is also shown that the nonadiabatic effect plays a crucial role in tuning the bandwidth of the subplateau.

A simple scheme is presented to generate $N$-qubit $W$ states with rf superconducting quantum interference devices (SQUIDs) in cavity QED through adiabatic passage. Because of the achievable strong coupling for rf SQUID qubits embedded in cavity QED, we can get the desired state with high success probability. Furthermore, the scheme is insensitive to the position inaccuracy of the rf SQUID. Numerical simulation shows that, by using present experimental techniques, we can achieve our scheme with very high success probability, and the fidelity could eventually be unity with the help of dissipation.

By incorporating the zero-point energy contribution we derive simple and accurate extensions of the usual Thomas-Fermi (TF) expressions for the ground-state properties of trapped Bose-Einstein condensates that remain valid for an arbitrary number of atoms in the mean-field regime. Specifically, we obtain approximate analytical expressions for the ground-state properties of spherical, cigar-shaped, and disk-shaped condensates that reduce to the correct analytical formulas in both the TF and the perturbative regimes, and remain valid and accurate in between these two limiting cases. Mean-field quasi-one-dimensional (quasi-1D) and -2D condensates appear as simple particular cases of our formulation. The validity of our results is corroborated by an independent numerical computation based on the 3D Gross-Pitaevskii equation.