We study the ancilla-free $1\to 2$ phase-covariant telecloning for qudits. We show that the fidelity of the two clones can probabilistically reach that of the clones in the optimal $1\to 2$ phase-covariant cloning (involving an ancilla). More interestingly, that can realize the above nonlocal cloning tasks are suitable nonmaximally entangled states rather than the maximally entangled states.

It was shown by Verstraete et al. [Phys. Rev. A 65, 052112 (2002)] that by stochastic local operations and classical communication, a pure state of four qubits can be transformed to a state belonging to one of a set of nine families of states. By using selective partial transposition, we construct partial $K$-way negativities to measure the genuine four-partite, tripartite, and bipartite entanglements of single-copy states belonging to the nine families of four-qubit states. Partial $K$-way negativities are polynomial functions of local invariants characterizing each family of states, as such, entanglement monotones.

We present a detailed experimental study of the Uhrig dynamical decoupling (UDD) sequence in a variety of noise environments. Our qubit system consists of a crystalline array of ${{}^9\text{B}\text{e}}^{+}$ ions confined in a Penning trap. We use an electron-spin-flip transition as our qubit manifold and drive qubit rotations using a 124 GHz microwave system. We study the effect of the UDD sequence in mitigating phase errors and compare against the well known Carr-Purcell-Meiboom-Gill-style multipulse spin echo as a function of pulse number, rotation axis, noise spectrum, and noise strength. Our results agree well with theoretical predictions for qubit decoherence in the presence of classical phase noise, accounting for the effect of finite-duration $\pi$ pulses. Finally, we demonstrate that the Uhrig sequence is more robust against systematic over- or under-rotation and detuning errors than is multipulse spin echo, despite the precise prescription for pulse timing in UDD.

Hollow atoms in which the $K$ shell is empty while the outer shells are populated allow studying a variety of important and unusual properties of atoms. The diagram x-ray emission lines of such atoms, the $K^h{\alpha }_{1,2}$ hypersatellites (HSs), were measured for the $3d$ transition metals, $Z=23–30$, with a high energy resolution using photoexcitation by monochromatized synchrotron radiation. Good agreement with ab initio relativistic multiconfigurational Dirac-Fock calculations was found. The measured HS intensity variation with the excitation energy yields accurate values for the excitation thresholds, excludes contributions from shake-up processes, and indicates domination near threshold of a nonshake process. The $Z$ variation of the HS shifts from the diagram line $K{\alpha }_{1,2}$, the $K^h{\alpha }_1-K^h{\alpha }_2$ splitting, and the $K^h{\alpha }_1/K^h{\alpha }_2$ intensity ratio, derived from the measurements, are also discussed with a particular emphasis on the QED corrections and Breit interaction.

The $K$-shell diagram ($K{\alpha }_{1,2}$ and $K{\beta }_{1,3}$) and hypersatellite (HS) $\left(K^h{\alpha }_{1,2}\right)$ spectra of Y, Zr, Mo, and Pd have been measured with high energy-resolution using photoexcitation by 90 keV synchrotron radiation. Comparison of the measured and ab initio calculated HS spectra demonstrates the importance of quantum electrodynamical (QED) effects for the HS spectra. Phenomenological fits of the measured spectra by Voigt functions yield accurate values for the shift of the HS from the diagram lines, the splitting of the HS lines, and their intensity ratio. Good agreement with theory was found for all quantities except for the intensity ratio, which is dominated by the intermediacy of the coupling of the angular momenta. The observed deviations imply that our current understanding of the variation of the coupling scheme from $LS$ to $jj$ across the periodic table may require some revision.

Differential cross sections for elastic scattering of electrons from dimethylsulfide and dimethylsulfoxide in the energy range from 30 to 500 eV are presented. The cross sections have been measured using a crossed-beam-type high-resolution electron spectrometer. The measured cross sections have been put on an absolute scale using the relative flow technique. The measured differential cross sections show an increase in the midangles at 30 and 50 eV for both the molecules that is characteristic of resonant enhanced $d$-wave scattering. Total and momentum-transfer cross sections were derived by integrating over all angles after extrapolating the data to forward and backward angles using a least-squares fitting procedure based on the Legendre polynomial expansion. Independent-atom-model-based theoretical calculations incorporating static, exchange, and polarization potentials are also reported and compared with the experimental cross sections. For energies lower than 100 eV, it is seen that the independent-atom-model calculations fail to predict the qualitative behavior of the differential cross sections correctly, while at energies greater than 100 eV it seems to describe the data adequately. The effect of polarization and enhancement of cross sections through $d$-wave scattering at low energies is also analyzed.

In this work, we examine a system for coherent transfer of atoms into a Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein condensates in different hyperfine ground states held in the same dc magnetic trap. By means of a pulsed transfer of atoms, we are able to show a clear resonance in the timing of the transfer, both in temperature and in number, from which we draw conclusions about the underlying physical process. The results are discussed in the context of the recently demonstrated pumped atom laser.

We investigate experimentally and theoretically the coherent population trapping (CPT) effect occurring in ${}^{87}\text{R}\text{b}$ $D_1$ line due to the interaction with linearly polarized laser light ($\text{lin}\parallel \text{lin}$ CPT). In this configuration, the coherence is strongly influenced by the structure of the excited state; consequently, the quantum interference between dark states is an essential feature of this interaction scheme. We study the $\text{lin}\parallel \text{lin}$ CPT resonance as a function of the laser optical detuning. The comparison between experimental and theoretical results allows us to quantify the contribution from different dark states to the total signal. Based on these results, we investigate the signal depending on both the pressure broadening of the optical transition and the laser linewidth, and we find in which conditions the laser linewidth does not degrade the $\text{lin}\parallel \text{lin}$ CPT resonance.

We present a technique to synthesize high-power single-cycle pulses in the visible and ultraviolet ranges by coherent superposition of a multiband octave-spanning spectrum obtained by highly nondegenerate cascaded four-wave mixing of femtosecond pulses in bulk isotropic nonresonant media. The generation of coherent spectra spanning over two octaves in bandwidth is experimentally demonstrated using a thin fused silica slide. Full characterization of the intervening multicolored fields using frequency-resolved optical gating, where multiple cascaded orders have been measured simultaneously, supports the possibility of direct synthesis of near-single-cycle 2.2 fs visible-uv pulses without recurring to complex amplitude or phase control, which should enable many applications in science and technology.

We theoretically investigate the dually dressed electromagnetically induced transparency, and the multidressed four-wave mixing (FWM) and six-wave mixing (SWM) processes in an inverted-$Y$-type atomic system with Zeeman sublevels. The results show that the Zeeman degeneracy of the dark states can be lifted by the dressing field as its intensity is increased. Moreover, the derived analytical expressions indicate that one can, for example, selectively create secondary dark states on the multi-Zeeman-sublevel dark states (by tuning the coupling field), distinguish two different types of dark states generated in two FWM processes (by properly controlling the coupling field intensity), and selectively enhance multi-FWM signals coming from various paths consisting of split Zeeman sublevels (by tuning the dressing field). The SWM signals can be either enhanced or suppressed by controlling the dressing field.

We investigate the decay of entanglement of a generalized $N$-qudit Greenberger-Horne-Zeilinger state with each qudit passing through independently in a quantum noisy channel. By studying the time at which the entanglement completely vanishes and the time at which the entanglement becomes arbitrarily small, we try to find how the robustness of entanglement is influenced by the dimension $d$ and the number of particles $N$.

We describe the precise mechanism behind the rapid and large spectral broadening in the early stages of supercontinuum generation in submicron-core glass waveguides. The first spectral and temporal breathing period of higher-order solitons activates the solitonic resonant radiation by means of energy bursts. We demonstrate that this “activation length” is largely independent of the Raman effect but can be efficiently controlled by changing the input pulse chirp. Energy transfer between the input pulse and its resonant radiations has a marked steplike character, and can reach a large efficiency. This will lead to the design of devices based on millimeter-size fibers, which are able to emit a clean, coherent, and controllable spectrum.

We discuss in detail how non-Markovian open system dynamics can be described in terms of quantum jumps [J. Piilo et al., Phys. Rev. Lett. 100, 180402 (2008)]. Our results demonstrate that it is possible to have a jump description contained in the physical Hilbert space of the reduced system. The developed non-Markovian quantum jump approach is a generalization of the Markovian Monte Carlo wave function (MCWF) method into the non-Markovian regime. The method conserves both the probabilities in the density matrix and the norms of the state vectors exactly and sheds new light on non-Markovian dynamics. The dynamics of the pure state ensemble illustrates how local-in-time master equation can describe memory effects and how the current state of the system carries information on its earlier state. Our approach solves the problem of negative jump probabilities of the Markovian MCWF method in the non-Markovian regime by defining the corresponding jump process with positive probability. The results demonstrate that in the theoretical description of non-Markovian open systems, there occurs quantum jumps which recreate seemingly lost superpositions due to the memory.

I show how applying a symplectic Gram-Schmidt orthogonalization to the normalizer of a quantum code gives a different way of determining the code’s logical operators. This approach may be more natural in the setting where we produce a quantum code from classical codes because the generator matrices of the classical codes form the normalizer of the resulting quantum code. This technique is particularly useful in determining the logical operators of an entanglement-assisted code produced from two classical binary codes or from one classical quaternary code. Finally, this approach gives additional formulas for computing the amount of entanglement that an entanglement-assisted code requires.

We consider a charged particle moving parallel to the surface of a metal film covering on the semi-infinite dielectric substrate with constant speed. By means of the linearized quantum hydrodynamic theory, the induced electron gas density and the stopping power are studied, taking into account the quantum statistical and quantum diffraction effects. The calculation results show that an oscillatory wake field appears apparently behind the particle at both of the surfaces of the metal film and the effect of the film thickness on the electron gas density cannot be neglected when film is thinner. Besides, the dependence of the stopping power on the film thickness, particle position, and the density parameter are analyzed. Finally, the stopping power of our results is compared with those based on the local frequency-dependent dielectric approach.

We examine the phase diagram of a simple-cubic optical lattice half filled by two species of fermionic atoms with a repulsive $s$-wave contact interaction. We use the Hartree approximation in the regime of weaker interactions and a Hubbard model approximation in the Mott insulating phase. The regime where the Néel phase of this system is likely to be most accessible to experiments is at intermediate lattice strengths and interactions, and our two approximations agree fairly well in this regime. We discuss the various issues that may determine where in this phase diagram the Néel phase is first produced and detected experimentally, and analyze the quantum phases that occur in the intermediate lattice strength regime.

Terahertz (THz) emissions of an isolated atom in an ultrashort (100 fs) laser field are simulated by solving the time-dependent Schrödinger equation. From numerical calculations with one- and three-dimensional hydrogen atom models and a short-range shallow potential model, it can be concluded that continuum THz emissions occur more readily following transitions involving intermediate states above rather than those well below the ionization threshold of the system. Line-shaped THz emissions from transitions between high-lying Rydberg states are also found. The models are also used to describe the observed enhanced terahertz emissions with a superposed second-order harmonic laser field or a spatially constant electric field. The dependence of the THz field strength on the intensities of the fundamental laser field and the superposed field is also examined. Strong field approximation is extended to analyze the general features of THz emissions resulting from continuum free-free transitions of an electron in strong laser fields. These calculations contribute to an understanding of the THz emission processes when strong laser fields interact with atomic and molecular systems that have larger ionization potentials and where multiphoton processes are involved in order to generate THz emissions effectively.

We consider an ultracold rotating Bose gas in a harmonic trap close to the critical angular velocity, so that the system can be considered to be confined to the lowest Landau level. With this assumption we prove that the Gross-Pitaevskii energy functional accurately describes the ground-state energy of the corresponding $N$-body Hamiltonian with contact interaction provided the total angular momentum $L$ is much less than $N^2$. While the Gross-Pitaevskii energy is always an obvious variational upper bound to the ground-state energy, a more refined analysis is needed to establish it as an exact lower bound. We also discuss the question of Bose-Einstein condensation in the parameter range considered. Coherent states together with inequalities in spaces of analytic functions are the main technical tools.

In this paper, we investigate the ground-state properties of a bosonic Tonks-Girardeau (TG) gas confined in a one-dimensional periodic potential. The single-particle reduced density matrix is computed numerically for systems up to $N=265$ bosons. Scaling analysis of the occupation number of the lowest orbital shows that there are no Bose-Einstein condensation (BEC) for the periodically trapped TG gas in both commensurate and incommensurate cases. We find that, in the commensurate case, the scaling exponents of the occupation number of the lowest orbital, the amplitude of the lowest orbital and the zero-momentum peak height with the particle numbers are 0, $-0.5$ and 1, respectively, while in the incommensurate case, they are 0.5, $-0.5$, and 1.5, respectively. These exponents are related to each other in a universal relation.

We present a series of theoretical studies of the boundary between a superfluid and a normal region in a partially polarized gas of strongly interacting fermions. We present mean-field estimates of the surface energy in this boundary as a function of temperature and scattering length. We discuss the structure of the domain wall, and use a previously introduced phenomonological model to study its influence on experimental observables. Our microscopic mean-field calculations are not consistent with the magnitude of the surface tension found from our phenomonological modeling of data from the Rice University experiments. We conclude that one must search for novel mechanisms to explain the experiments.