Intensities of ${10}^{22}$ W ${\mathrm{cm}}^{-2}$ have been reached and it is expected that this will be increased by two orders of magnitude in the near future. At these intensities the radiation reaction force is important, especially in calculating the terminal velocity of an electron. The following briefly describes some of the problems of the existing most well-known equations and describes an approach based on conservation of energy. The resulting equation is compared to the Landau Lifshitz and Ford O’Connell equations, and laboratory tests are proposed.

Internal symmetries can be used to classify multiple solutions to the time-energy canonical commutation relation (TE-CCR). The dynamical behavior of solutions to the TE-CCR possessing particular internal symmetries involving time reversal differ significantly from solutions to the TE-CCR without those particular symmetries, implying a connection between the internal symmetries of a quantum system, its internal unitary dynamics, and the TE-CCR.

In order to explore repulsive Casimir or van der Waals forces between solid materials with liquid as the intervening medium, we analyze dielectric data for a wide range of materials as, for example, (p)olytetrafluoroethylene, polystyrene, silica, and more than 20 liquids. Although significant variation in the dielectric data from different sources exists, we provide a scheme based on measured static dielectric constants, refractive indices, and applying Kramers-Kronig consistency to dielectric data to create accurate dielectric functions at imaginary frequencies. The latter is necessary for more accurate force calculations via the Lifshitz theory, thereby allowing reliable predictions of repulsive Casimir forces.

Heavy He-like ions are considered to be promising candidates for atomic parity-nonconservation (PNC) studies, thanks to their relatively simple atomic structure and the significant mixing between the almost degenerate (for the atomic numbers $Z~64$ and $Z~91$) opposite-parity levels $1s2s\hspace{0.5em}{}^1{S}_0$ and $1s2p\hspace{0.5em}{}^3{P}_0$. A number of experiments exploiting this level mixing have been proposed, and their implementation requires a precise knowledge of the $2\hspace{0.5em}{}^3{P}_0$–$2\hspace{0.5em}{}^1{S}_0$ energy splitting for different nuclear charges and isotopes. In this paper we performed a theoretical analysis of the level splitting, employing the relativistic many-body perturbation theory and including QED corrections for all isotopes in the intervals $54⩽Z⩽71$ and $86⩽Z⩽93$. Possible candidates for future experimental PNC studies are discussed.

We report on an energy-sensitive imaging detector for studying the fragmentation of polyatomic molecules in the dissociative recombination of fast molecular ions with electrons. The system is based on a large area ($10\times 10$ cm${}^2$) position-sensitive, double-sided Si-strip detector with $128$ horizontal and $128$ vertical strips, whose pulse height information is read out individually. The setup allows us to uniquely identify fragment masses and is thus capable of measuring branching ratios between different fragmentation channels, kinetic energy releases, and breakup geometries as a function of the relative ion-electron energy. The properties of the detection system, which has been installed at the Test Storage Ring (TSR) facility of the Max-Planck Institute for Nuclear Physics in Heidelberg, is illustrated by an investigation of the dissociative recombination of the deuterated triatomic hydrogen cation ${\mathrm{D}}_2$H${}^{+}$. A huge isotope effect is observed when comparing the relative branching ratio between the ${\mathrm{D}}_2$ $+$ H and the HD $+$ D channel; the ratio $2B$(D${}_2$ $+$ H)/$B$(HD $+$ D), which is measured to be $1.27\pm 0.05$ at relative electron-ion energies around $0$ eV, is found to increase to $3.7\pm 0.5$ at $~$5 eV.

Few-photon-induced breakup of helium is studied using a newly developed ab initio numerical framework for solving the six-dimensional time-dependent Schrödinger equation. We present details of the method and calculate (generalized) cross sections for the process of two-photon nonsequential (direct) double ionization at photon energies ranging from 39.4 to 54.4 eV, a process that has been very much debated in recent years and is not yet fully understood. In particular, we have studied the convergence property of the total cross section in the vicinity of the upper threshold ($~54.4$ eV) versus the pulse duration of the applied laser field. We find that the cross section exhibits an increasing trend near the threshold, as has also been observed by others, and show that this rise cannot solely be attributed to an unintended inclusion of the sequential two-photon double ionization process caused by the bandwidth of the applied field.

We propose a theoretical method to calculate the infrared (IR) laser-assisted photoabsorption cross sections over a broad energy range by a single calculation. In this method we define an initial wave function as the product of the dipole operator and the atomic ground state, propagate the initial wave function in the IR laser field with different initial phases, then calculate the generalized autocorrelation function, which is defined as the averaged value of the autocorrelation function over the initial phase from 0 to $2\pi$ (or one IR optical cycle). The IR laser-assisted photoabsorption cross sections are obtained by the Fourier transform of the generalized autocorrelation function. We apply this method to study the IR laser-assisted photoabsorption of He atoms. From the simulation results, we see that the IR laser field affects not only the resonant position but also the lifetime or the width of the bound states. This photoabsorption cross section is an important quantity to analyze the IR-laser-assisted dynamical processes by an attosecond pulse, a pulse train, or a free-electron laser.

We examine a two-dimensional mixture of single-component fermions and dipolar bosons. We calculate the self-enregies of the fermions in the normal state and the Cooper-pair channel by including first-order vertex correction to derive a modified Eliashberg equation. We predict the appearance of superfluids with various nonstandard pairing symmetries at experimentally feasible transition temperatures within the strong-coupling limit of the Eliashberg equation. Excitations in these superfluids are anyonic and follow non-Abelian statistics.

In this article we comment on the relation between the ac Josephson effect and the coherent oscillations of a Bose-Einstein condensate confined to a double-well potential. The goal is to elucidate the extent to which the latter is a realization of the former. We detail the correspondence between the two oscillation frequencies, that emerges in the high occupation limit of the double-well potential. We show that in the latter thermodynamic limit the effective one-particle interwell coupling vanishes with the system size, leading to oscillation frequency that depends only on the interwell imbalance, consistent with the ac Josephson effect frequency.

We show that interplay of linear attractive (repulsive) boundary with inhomogeneous repulsive (attractive) interatomic interactions results in nonlinear localized surface modes (surface solitons), some of which are stable. We consider several example systems describing interaction of inhomogeneous Bose-Einstein condensates with rigid surfaces and allowing for exact solutions. The stability of the obtained modes is analyzed analytically and numerically. Stable localized surface modes are found and dynamics of the unstable modes is described.

We investigate the dynamics of two tunnel-coupled two-dimensional degenerate Bose gases. The reduced dimensionality of the clouds enables us to excite specific angular momentum modes by tuning the coupling strength, thereby creating striking patterns in the atom density profile. The extreme sensitivity of the system to the coupling and initial phase difference results in a rich variety of subsequent dynamics, including vortex production, complex oscillations in relative atom number, and chiral symmetry breaking due to counter-rotation of the two clouds.

We study the translational motion of an atom in the vicinity of a weakly driven nanofiber with two fiber-Bragg-grating mirrors. We calculate numerically and analytically the force, the friction coefficients, and the momentum diffusion. We find that the spatial dependences of the force, the friction coefficients, and the momentum diffusion are very complicated due to the evanescent-wave nature of the atom-field coupling as well as the effect of the van der Waals potential. We show that the time development of the mean number of photons in the cavity closely follows the translational motion of the atom through the nodes and antinodes of the fiber-guided cavity standing-wave field even though the cavity finesse is moderate, the cavity is long, and the probe field is weak.

We theoretically analyze the effectiveness of multiple-pulse laser alignment methods for asymmetric-top molecules. As an example, we choose SO${}_2$ and investigate the alignment dynamics induced by two different sequences, each consisting of four identical laser pulses. Each sequence differs only in the time delay between the pulses. Equally spaced pulses matching the alignment revival of the symmetrized SO${}_2$ rotor model are exploited in the first sequence. The pulse separations in the second sequence are short compared to the rotation dynamics of the molecule and monotonically increase the degree of alignment until the maximum alignment is reached. We point out the significant differences between the alignment dynamics of SO${}_2$ treated as an asymmetric-top and a symmetric-top rotor, respectively. We also explain why the fast sequence of laser pulses creates considerably stronger one-dimensional molecular alignment for asymmetric-top molecules. In addition, we show that multiple-pulse trains with elliptically polarized pulses do not enhance one-dimensional alignment or create three-dimensional alignment.

Quantum discord was proposed as a measure of the quantumness of correlations. There are at least three different discordlike quantities, two of which determine the difference between the efficiencies of a Szilard’s engine under different sets of restrictions. The three discord measures vanish simultaneously. We introduce an easy way to test for zero discord, relate it to the Cerf-Adami conditional entropy and show that there is no simple relation between the discord and the local distinguishability.

In this article we outline a method for generating linear optics circuits that encode quantum-error-correcting codes. Using this method we produce a single-error-correcting code encoding one wave packet over five which can be implemented using linear optics and feed-forward correction. This code improves on the capacity of the best known code that can be implemented using linear optics and saturates the lower bound for the number of carriers needed for a single-error-correcting code. Our code can correct arbitrary single errors that occur randomly on each wave packet corresponding to a non-Gaussian error model, thus circumventing the so-called no-go theorem for Gaussian quantum-error correction.

We theoretically investigate the collective modes of imbalanced two-component one-dimensional Fermi gases with attractive interactions. This is done for trapped and untrapped systems both at zero and nonzero temperature, using self-consistent mean-field theory and the random phase approximation. We discuss how the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state can be detected and the periodicity of the associated density modulations determined from its collective mode spectrum. We also investigate the accuracy of the single-mode approximation for low-lying collective excitations in a trap by comparing frequencies obtained via sum rules with frequencies obtained from direct collective mode calculations. It is found that, for collective excitations where the atomic clouds of the two spin-species oscillate largely in phase, the single-mode approximation holds well for a large parameter regime. Finally, we investigate the collective mode spectrum obtained by parametric modulation of the coupling constant.

We compute binding energies and root-mean-square radii for weakly bound systems of $N=4$ and $5$ identical bosons. Ground and first excited states of an $N$-body system appear below the threshold for binding the system with $N-1$ particles. Their root-mean-square radii approach constants in the limit of weak binding. Their probability distributions are on average located in nonclassical regions of space which result in universal structures. Radii decrease with increasing particle number. The ground states for more than five particles are probably nonuniversal, whereas excited states may be universal.

The resonance fluorescence emitted by a system of two dipole-dipole interacting nearby four-level atoms in a $J=1/2\leftrightarrow J=1/2$ configuration is studied. This setup is the simplest realistic model system which provides a complete description of the (inter-atomic) dipole-dipole interaction for arbitrary orientation of the inter-atomic distance vector, and at the same time allows for intra-atomic spontaneously generated coherences. Our main interest is the interplay of both these different coupling mechanisms. We discuss different methods to analyze the contribution of the various vacuum-induced coupling constants to the total resonance fluorescence spectrum. These allow us to find a dressed state interpretation of the contribution of the different inter-atomic dipole-dipole couplings to the total spectrum. We further study the role of the spontaneously generated coherences, and identify two different contributions to the single-particle vacuum-induced couplings. We show that they have a noticeable impact on the total resonance fluorescence spectrum down to small inter-atomic distances, even though the dipole-dipole coupling constants then are much larger in magnitude than the the single-particle coupling constants. Interestingly, we find that the inter-atomic couplings can induce an effect of the intra-atomic spontaneously generated coherences on the observed spectra which is not present in single-atom systems.

We consider soliton dynamics and stability in a nonlinear lattice formed by alternating domains with focusing cubic and saturable nonlinearities. We find that in such lattices, solitons centered on cubic domains may be stabilized even in two-dimensional geometries, in spite of their intrinsic catastrophic instability in the absence of the lattice. Solitons centered on saturable domains are always unstable.