A semiclassical kinetic model is developed to simulate the plasmon excitation of nanotubes and the transport of charged particles moving through nanotubes. With the introduction of electron band structure, the analytical expressions of the dielectric function and the energy loss function are obtained for zigzag and armchair nanotubes of metallic properties, respectively. Numerical results display several very distinct peaks in the curves of loss function, showing effects from the collective excitation. Furthermore, the stopping power and self-energy are calculated while charged particles move along the axis of nanotubes with different geometries, under the influence of friction coefficients. For small enough friction coefficients, it can be regarded as a case with zero damping. But as the damping factor increases, not only the self-energy and stopping power decrease in magnitude, but also their extrema move to lower velocities, without distinct threshold effects.

We present and analyze results of ab initio computations of nonsequential double ionization of the hydrogen molecule in a few-cycle intense laser pulse. To this end, we have used a model of planar molecules with static nuclei, in which the electronic center-of-mass motion is restricted along the polarization direction of the linearly polarized laser. Alignment of the internuclear axis parallel and perpendicular to the polarization axis of the laser field are considered. We show how the relative electron dynamics, parallel and transversal to the field polarization axis, can be used to resolve the different pathways to nonsequential double ionization. Besides the well-known mechanisms, namely, simultaneous emission of an electron pair upon rescattering and recollision-induced excitation with subsequent field ionization, we identify two additional pathways. According to our interpretation the latter are due to a decay of doubly excited states, created during the recollision event, and correlated electron emission after soft recollision. Finally, we analyze the relative strengths of the different contributions to nonsequential double ionization as a function of the laser intensity.

The observation of an electron electric-dipole moment (EEDM) would have major ramifications for the standard model of physics. Polar molecules offer a near-ideal laboratory for such searches due to the large effective electric field $\left({\mathbf{F}}_{\mathrm{eff}}\right)$, on order of tens of GV/cm that can be easily oriented in the laboratory frame. We present an improved method for simply and accurately determining ${\mathbf{F}}_{\mathrm{eff}}$, in a heavy polar molecule, allowing for a quick determination of candidates for an EEDM experiment. We apply this method to ThO and $\mathrm{Th}{\mathrm{F}}^{+}$, both of which possess metastable ${}^3\Delta$ electronic states. The values of ${\mathbf{F}}_{\mathrm{eff}}$ in ThO and $\mathrm{Th}{\mathrm{F}}^{+}$ are estimated to be $104\mathrm{GV}∕\mathrm{cm}$ and $90\mathrm{GV}∕\mathrm{cm}$, respectively, making them two of the best known candidates for the EEDM search.

We present and analyze results of the relativistic coupled-cluster calculation of energies, hyperfine constants, and dipole matrix elements for the $2s$, $2p_{1∕2}$, and $2p_{3∕2}$ states of Li atom. The calculations are complete through the fourth order of many-body perturbation theory for energies and through the fifth order for matrix elements and subsume certain chains of diagrams in all orders. A nearly complete many-body calculation allows us to draw conclusions on the convergence pattern of the coupled-cluster method. Our analysis suggests that the high-order many-body contributions to energies and matrix elements scale proportionally and provide a quantitative ground for semiempirical fits of ab initio matrix elements to experimental energies.

Given a real-valued phase-space function, it is a nontrivial task to determine whether it corresponds to a Wigner distribution for a physically acceptable quantum state. This topic has been of fundamental interest for a long time, and in a modern application, it can be related to the problem of entanglement detection for multimode cases. In this paper, we present a hierarchy of complete conditions for a physically realizable Wigner distribution. Our derivation is based on the normally ordered expansion, in terms of annihilation and creation operators, of the quasidensity operator corresponding to the phase-space function in question. As a by-product, it is shown that the phase-space distributions with elliptical symmetry can be readily diagonalized in our representation, facilitating the test of physical realizability. We also illustrate how the current formulation can be connected to the detection of bipartite entanglement for continuous variables.

We study collective interaction effects that result from the change of free quantum electrodynamic field fluctuations by one- and two-dimensional perfect metal structures. The Casimir interactions in geometries containing plates and cylinders is explicitly computed using partial wave expansions of constrained path integrals. We generalize previously obtained results and provide a more detailed description of the technical aspects of the approach. We find that the interactions involving cylinders have a weak logarithmic dependence on the cylinder radius, reflecting that one-dimensional perturbations are marginally relevant in 4D space time. For geometries containing two cylinders and one or two plates, we confirm a previously found nonmonotonic dependence of the interaction on the object’s separations which does not follow from pairwise summation of two-body forces. Qualitatively, this effect is explained in terms of fluctuating charges and currents and their mirror images.

In classical control theory, tracking refers to the ability to perform measurements and feedback on a classical system in order to enforce some desired dynamics. In this paper we investigate a simple version of quantum tracking, namely, we look at how to optimally transform the state of a single qubit into a given target state, when the system can be prepared in two different ways, and the target state depends on the choice of preparation. We propose a tracking strategy that is proved to be optimal for any input and target states. Applications in the context of state discrimination, state purification, state stabilization, and state-dependent quantum cloning are presented, where existing optimality results are recovered and extended.

In this paper we explore the use of a quantum optimization algorithm for obtaining low-energy conformations of protein models. We discuss mappings between protein models and optimization variables, which are in turn mapped to a system of coupled quantum bits. General strategies are given for constructing Hamiltonians to be used to solve optimization problems of physical, chemical, or biological interest via quantum computation by adiabatic evolution. As an example, we implement the Hamiltonian corresponding to the hydrophobic-polar model for protein folding. Furthermore, we present an approach to reduce the resulting Hamiltonian to two-body terms gearing toward an experimental realization.

A scheme to simulate the evolution of a restricted set of observables of a quantum system is proposed. The set comprises the spectrum-generating algebra of the Hamiltonian. Focusing on the simulation of the restricted set allows to drastically reduce the cost of the simulation. This reduction is the result of replacing the original unitary dynamics by a special open-system evolution. This open-system evolution can be interpreted as a process of weak measurement of the distinguished observables performed on the evolving system of interest. Under the condition that the observables are “classical” and the Hamiltonian is moderately nonlinear, the open-system dynamics displays a large time-scale separation between the relaxation of the observables and the decoherence of a generic state. This time-scale separation allows the unitary dynamics of the observables to be efficiently simulated by the open-system dynamics on the intermediate time scale. The simulation employs unraveling of the corresponding master equations into pure-state evolutions, governed by the stochastic nonlinear Schrödinger equation. The stochastic pure-state evolution can be simulated efficiently using a representation of the state in the time-dependent basis of the generalized coherent states, associated with the spectrum-generating algebra.

Quantum Fano inequality (QFI) in quantum information theory provides an upper bound to the entropy exchange by a function of the entanglement fidelity. We give various Fano-like upper bounds to the entropy exchange and QFI is a special case of these bounds. These bounds also give an alternate derivation of the QFI.

We present precision measurements with MHz uncertainty of the energy gap between asymptotic and well bound levels in the electronic ground state $X{{}^1\Sigma }_{\text{g}}^{+}$ of the ${{}^{39}\text{K}}_2$ molecule. The molecules are prepared in a highly collimated particle beam and are interrogated in a $\Lambda$-type excitation scheme of optical transitions to long range levels close to the asymptote of the ground state, using the electronically excited state ${A{}^1\Sigma }_{\text{u}}^{+}$ as the intermediate one. The transition frequencies are measured either by comparison with ${\text{I}}_2$ lines or by absolute measurements using a fs-frequency comb. The determined level energies were used together with Feshbach resonances from cold collisions of ${}^{39}\text{K}$ and ${}^{40}\text{K}$ reported from other authors to fit ground state potentials. Precise scattering lengths are determined and tests of the validity of the Born-Oppenheimer approximation for the description of cold collisions at this level of precision are performed.

The electromagnetic interaction of an atom or ion with an arbitrary spin nucleus is considered. The effective atomic interaction Hamiltonian is derived by a sequence of unitary transformations to separate out the total motion from the internal degrees of freedom. The obtained finite nuclear mass corrections modify the atomic energy levels in the magnetic field. We present resulting contributions to the electron $\mathit{g}$ factor, the NMR shielding factor, and the magnetic susceptibility.

Using both fluid and kinetic descriptions, with repulsive forces between nearby atoms included, we discuss the basic oscillations and waves of a cloud of ultracold atoms confined in a magneto-optical trap. The existence of a hybrid mode, with properties similar to both plasma and acoustic waves, is described in detail. Tonks-Dattner resonances for confined hybrid modes in a spherical cloud are discussed, and the prediction of a nonlinear coupling between the dipole resonance and the hybrid modes is considered. Landau damping processes and quasilinear diffusion in velocity space are also discussed.

The field theory of nonrelativistic fermions interacting via contact interactions can be used to calculate the properties of few-body systems of cold atoms confined in harmonic traps. The state-operator correspondence of nonrelativistic conformal field theory (NRCFT) shows that the energy eigenvalues (in oscillator units) of $N$ harmonically trapped fermions can be calculated from the scaling dimensions of $N$-fermion operators in the NRCFT. They are also in one-to-one correspondence with zero energy, scale-invariant solutions to the $N$-body problem in free space. We show that these two mappings of the trapped fermion problem to free space problems are related by an automorphism of the $SL\left(2,R\right)$ algebra of the conformal symmetry of fermions at the unitary limit. This automorphism exchanges the internal Hamiltonian of the gas with the trapping potential and hence provides a method for deriving virial theorems for trapped Fermi gases at the unitary limit. We also show that the state-operator correspondence can be applied directly in three spatial dimensions by calculating the scaling dimensions of two- and three-fermion operators and finding agreement with known exact results for energy levels of two and three trapped fermions at the unitary limit.

The time-dependent extended Gross-Pitaevskii equation for Bose-Einstein condensates with attractive $1/r$ interaction is investigated with both a variational approach and numerically exact calculations. We show that these condensates exhibit signatures known from the nonlinear dynamics of autonomous Hamiltonian systems. The two stationary solutions created in a tangent bifurcation at a critical value of the scattering length are identified as elliptical and hyperbolical fixed points, corresponding to stable and unstable stationary states of the condensate. The stable stationary state is surrounded by elliptical islands, corresponding to condensates periodically oscillating in time, whereas condensate wave functions in the unstable region undergo a collapse within finite time. For negative scattering lengths below the tangent bifurcation no stationary solutions exist, i.e., the condensate is always unstable and collapses.

We demonstrate experimentally coupled active-resonator-induced transparency in a fiber system. We show that the use of ${\mathrm{Er}}^{3+}$-doped fibers can compensate for the optical losses leading to a high transparency of the system. Using a Mach-Zehnder fiber interferometer, we measure the dispersion properties of our coupled active resonators under different pumping rates. We show that the active feature of the system allows us to engineer the different orders of its artificial dispersion. This experimental demonstration shows the potential of active coupled resonators for dispersion tailoring and slow-light applications.

We investigate how evanescent cylindrical vector waves can be shaped by radiationless electromagnetic interference. It is shown that properly designed aperture fields result in relatively uniform intensity distributions that can be positioned a given distance away from the aperture. Our study suggests that cylindrical evanescent vector waves may be shaped into subwavelength focal spots and holes using suitable apertures.

It is proposed that observed $1/f$ laser frequency noise in rare-earth-metal-doped optical fiber lasers is caused by diffusion of local entropy fluctuations associated with random spontaneous emission events. This heat generation is directly associated with the broad emission spectrum of rare-earth-metal-doped laser glasses. Using data from a well characterized erbium-doped fiber laser, it is shown that the power spectral density of frequency fluctuations resulting from this mechanism is able to achieve excellent agreement with experiment. The proposed theory is expected to be generally applicable to broadly emitting solid-state gain media.

The nonequilibrium evolution of the block entanglement entropy is investigated in the $XY$ chain in a transverse magnetic field after the Hamiltonian parameters are suddenly changed from and to arbitrary values. Using Toeplitz matrix representation and multidimensional phase methods, we provide analytic results for large blocks and for all times, showing explicitly the linear growth in time followed by saturation. The consequences of these analytic results are discussed and the effects of a finite block length is taken into account numerically.

Electric-dipole moments of paramagnetic atoms can provide important insights into a unique kind of CP violation involving Higgs-boson-mediated interactions between leptons and hadrons. We report a limit for the coupling constant of such an interaction by combining the results of our relativistic many-body calculations and experimental data on the electric-dipole moment of atomic thallium. The importance of electron correlation in determining this limit is highlighted and its significance in the context of particle physics and cosmology is pointed out.