We have demonstrated a detection scheme for atom laser beams that allows for a continuous measurement of the atom density and readout of the data in real time. The atoms in the atom laser beam are transferred locally from the lower to the upper hyperfine ground state of ${}^{87}\mathrm{Rb}$ by coherent coupling and are subsequently detected by an absorption measurement. The detection does not affect the Bose-Einstein condensate in the magnetic trap or the atom laser beam outside the detection region.

We show that two Raman generators which have different Raman transition frequencies and are used in series result in a multiplicative increase in the total number of generated sidebands. When phase-corrected, these sidebands synthesize to a train of randomly timed single-cycle pulses. For series generators on the rotational transitions of molecular ${\mathrm{D}}_2$ $(J=\overrightarrow{0}2)$ and ${\mathrm{H}}_2$ $(J=\overrightarrow{1}3),$ each with 40 modes, the average peak power enhancement is 1600 and the average duration between random pulses is 1.74 ps.

In our model a fixed Hamiltonian acts on the joint Hilbert space of a quantum system and its controller. We show conditions under which measurements, state preparations, and unitary implementations on the system can be performed by quantum operations on the controller only. It turns out that a measurement of the observable $A$ and an implementation of the one-parameter group $\exp \mathrm{}\left(\mathrm{iAr}\right)\mathrm{}$ can be performed by almost the same sequence of control operations. Furthermore, measurement procedures for $A+B,$ for $\mathrm{}(AB+BA),$ and for $i\lfloor A,B\rfloor$ can be constructed from measurements of $A$ and $B.\mathrm{}$ This shows that the algebraic structure of the set of observables can be explained by the Lie group structure of the unitary evolutions on the joint Hilbert space of the measuring device and the measured system. A spin chain model with nearest-neighborhood coupling shows that the border line between controller and system can be shifted consistently.

It is shown that the models recently proposed by Meyer, Kent, and Clifton (MKC) exhibit a novel kind of contextuality, which we term existential contextuality. In this phenomenon it is not simply the pre-existing value but the actual existence of an observable which is context dependent. This result confirms the point made elsewhere, that the MKC models do not, as the authors claim, “nullify” the Kochen-Specker theorem. It may also be of some independent interest.

The ultimate limits of continuous-variable single-mode quantum teleportation due to absorption are studied, with special emphasis on (quasi-) monochromatic optical fields propagating through fibers. It is shown that even if an infinitely squeezed two-mode squeezed vacuum were used, the amount of information that would be transferred quantum mechanically over a finite distance is limited and effectively approaches zero on a length scale that is much shorter than the (classical) absorption length. The state-dependent teleportation fidelity can be close to unity only for short distances. To realize the largest possibly fidelity, asymmetrical equipment must be used, where the source of the two-mode squeezed vacuum is nearer to Alice than to Bob and as a consequence the coherent displacement performed by Bob cannot be chosen independently of the transmission lengths.

It is shown that the yield of relativistic positronium atoms in photoproduction on extended targets is much larger than usually accepted. The cause of such a difference is transparent. At high energies, when the positronium atom formation time ${\tau }_f$ becomes greater than the target length $L,$ it is the free $e^{+}{e}^{-}$ pair that propagates through the target and the formation of positronium atoms takes place out of the target. In the framework of the light-cone technique we consider the interaction of an $e^{+}{e}^{-}$ pair with the screened Coulomb field of atoms in matter and obtain the analytical expressions for relativistic positronium atoms photoproduction cross sections on extended targets. The relation to free pair photoproduction on extended targets is discussed.

We present an explicit analytical construction of highly correlated triply excited hollow states in Coulombic three-electron systems. The construction is based on the simple idea that the three electrons will orient themselves in maximally polarized Stark states along three different axes with 120° between them to minimize their mutual repulsion. This ansatz for the three-electron state, supplemented with an external rotational average and proper antisymmetrization, produces configuration-interaction mixing coefficients in good agreement with data obtained from ab initio calculations. Our ansatz leads to a simple and fairly accurate Z-scaling relation for energy splittings and dipole matrix elements along the lithium isoelectronic sequence. Despite our prediction of isomorphic correlation patterns and corresponding quasigood quantum numbers for L series of states, there is no numerical evidence that energies are well represented by rigid-rotor rotational spectra. We explain this by the explicit failure in multiply excited atoms of the nuclear and molecular physics theories of rotational structure.

A scaling method applied to plane-wave Born cross sections for electron-impact excitation of neutral atoms is modified and applied to Coulomb Born cross sections for excitations of singly charged ions. The modified scaling for singly charged ions is simpler than the scaling for neutral atoms. Moreover, the former converts Coulomb Born cross sections into accurate results comparable to the convergent close coupling results, as is the case for the scaling for neutral atoms. Comparisons to available theoretical and experimental data on excitations of ${\mathrm{He}}^{+},$ ${\mathrm{Mg}}^{+},$ and ${\mathrm{Zn}}^{+}$ are presented.

The energy loss and self-energy of electric dipoles in a free-electron gas are studied using the dielectric function formalism. Analytical expressions for low and high velocities and for different orientations of the dipole axis are obtained and compared with full numerical integrations using Lindhard’s dielectric function. The contributions from plasmon and individual excitations are calculated separately. Similar calculations were performed for diclusters or “extended dipoles” and for individual protons, and the results are compared. Several features arising from short-range dipolelike interactions are analyzed. Numerical estimations indicate the possibility of carrying out energy loss measurements on the interaction of polar molecules with solids.

Fourth-order Green’s function calculations have revealed many interesting features in the core-level spectra of ${\mathrm{Be}}_n$ and ${\mathrm{Mg}}_n$ $\mathrm{}(n=2,3,4\mathrm{})\mathrm{}$ clusters. The most striking of them are unusually low-lying intense satellites. These are absent in the respective atomic spectra and not observed in the spectra of typical molecules. An analysis in terms of localized configurations attributes these satellites to distinct interatomic processes. These processes comprise charge and energy transfer from one atom to neighboring atoms. The spectra are sensitive to the size and conformation of the clusters. This can be useful for the experimental identification of the clusters. The emerging physical picture of core ionization of small soft metal ${\mathrm{Be}}_n$ and ${\mathrm{Mg}}_n$ clusters is quite general and applicable to other weekly bound atomic and molecular clusters.

In this work we probe the time dynamics of a collisional process involving energy transfer in a sample of cold Rydberg atoms produced in a rubidium magneto-optical trap. The ${31S}_{1/2}$ population, produced by collisions between the ${29P}_{3/2}$ and ${29P}_{1/2,3/2}$ states, is monitored as a function of time through the pulsed-field ionization technique. The experimental results were compared with a dynamic model based on a two-body interaction using a ${1/R}^5$ potential. The model can reproduce well the time evolution of this collisional process. We are also able to explain the large electric-field range over which inelastic collisions are possible based on the existence of thresholds where collisional channels open and close.

The relativistic classical dynamics of hydrogenlike ions is investigated numerically in the presence of intense high-frequency laser pulses of intensity well above ${10}^{16}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\mathrm{-}2}$ and various pulse lengths up to several hundred cycles. With rising effective charge $Z,$ the stabilized electron dynamics is shown to be increasingly governed by the joint interplay of Coulomb attraction and Lorentz force in the laser-propagation direction, involving also so-called magnetic recollisions. With regard to the ionization behavior, the varying stabilization with increasing Z can be largely described by scaling the angular frequency and electric field strength by $Z^2$ and $Z^3,$ respectively, however, clear signatures appear also due to the increased role of relativity. For long pulses and slowly entering the relativistic regime, the enhanced adiabaticity of the pulse turn-on has insufficient influence because the breakdown of stabilization due to the Lorentz force will still be stronger due to the dominating role of the necessarily increased interaction time with the superintense laser field.

We study the dynamics of vortex lattice formation of a rotating trapped Bose-Einstein condensate by numerically solving the two-dimensional Gross-Pitaevskii equation, and find that the condensate undergoes elliptic deformation, followed by unstable surface-mode excitations before forming a quantized vortex lattice. The origin of the peculiar surface-mode excitations is identified to be phase fluctuations at the low-density surface regime. The obtained dependence of a distortion parameter on time and that on the driving frequency agree with the recent experiments by Madison et al. [Phys. Rev. Lett. 86, 4443 (2001)].

This paper renders two main results. One is a unified quantum master equation, which satisfies the detailed-balance relation and can serve as a convenient starting formulation to study the dissipative dynamics in a variety of systems in quantum optics and solid-state physics. Another is based on the proposed quantum master equation to study cavity quantum electrodynamics in the presence of $T_1$ energy relaxation and pure $T_2$ dephasing. Demonstrated in detail is also the effect of cavity field–absorber interaction on dissipation, which is neglected in the conventional theory.

We report the implementation of an entanglement transfer on a four-qubit liquid-state nuclear-magnetic resonance quantum information processor. This consists of creating an (pseudopure) entangled state among two directly coupled spins, and then transferring this two-spin state to another pair of spins whose direct interactions are negligible. Such transfers are expected to be an essential operation in scalable quantum computer architectures, and provide a useful benchmark for the coherent control available in specific implementations.

A Hamiltonian formulation of weighted-ensemble density-functional theory is provided by considering eigenstates of a super-Hamiltonian that consists of a sum of replicas of the physical Hamiltonian. For a nondegenerate physical Hamiltonian the replica permutational symmetry specified by the Young diagram $\Gamma \equiv [{\lambda }_1,{\lambda }_2,\dots ],$ where ${\lambda }_1>~{\lambda }_2>~\cdot \cdot \cdot$ and $|\Gamma |={\sum }_i{\lambda }_i,$ yields a super-ground state, which is equivalent to an ensemble average with weights ${\omega }_i={\lambda }_i/|\Gamma |,$ $i=1,2,\dots .$ A corresponding Hohenberg-Kohn theorem is derived, and an extension to degenerate physical Hamiltonians is proposed.

Fluctuations of light intensity in a laser with an intracavity nonlinear absorber are studied experimentally. Measurements are made close to the tricritical point by varying the operating parameters of the laser. Experimental results are in agreement with the theoretical predictions based on the nonlinear oscillator model of the laser in which both the third- and fifth-order nonlinearities in the field amplitude are retained.

Optimal control theory (OCT) has wide applicability in the quest for seeking optimal laser pulses in coherent control of quantum phenomena. We have revised OCT making it possible to distill robust electric fields realizable via femtosecond pulse-shaping technology. The simple pulse structures offer direct physical insight into the control mechanism and selectively isolate the most stable pathways involving only few frequencies. Moreover, a generalized functional makes a vital extension in including the laser system used in control experiments.

We formulate a theory of slow polaritons in atomic gases and apply it to the slowing down, storing, and redirecting of laser pulses in an electromagnetically induced transparency (EIT) medium. The normal modes of the coupled matter and radiation are determined through a full diagonalization of the dissipationless Hamiltonian. Away from the EIT resonance, where the polaritons acquire an excited-state contribution, lifetimes are introduced as a secondary step. With detuning included various four-wave mixing possibilities are analyzed. We investigate specifically the possibility of reverting a stopped polariton by reversing the control beam.

A self-consistent theory of a cylindrically shaped Bose-Einstein condensate (BEC) periodically modulated by a laser beam is presented. We show, both analytically and numerically, that modulational instability/stability is the mechanism by which wave functions of soliton type can be generated in a cylindrically shaped BEC subject to a one-dimensional optical lattice. The theory explains why bright solitons can exist in a BEC with positive scattering length and why condensates with negative scattering length can be stable and give rise to dark solitary pulses.