The dynamics of a two-mode Bose-Einstein condensate trapped in a double-well potential results approximately in an effective Rabi oscillation regime of exchange of population between both wells for sufficiently strong overlap between the modes functions and sufficiently large condensates. Facing the effective Rabi oscillation as a temporal atomic beam splitter we propose a nondestructive measurement process allowing an atomic homodyne detection, thus yielding indirect relative phase information about one of the two-mode condensates. This proposal is achieved through a secondary optical homodyne detection, in which the field is allowed to dispersively interact with one of the condensate modes inside an optical cavity.

In previous work, it was found that heat conduction limited the development of laser action at wavelengths below $50\mathrm{\AA }$. In this paper, we discuss the use of thin foils to limit these effects, and generate a high-density and -temperature plasma with low refractive index gradient. By using a relatively short $(\sim 100\mathrm{ps})$ first pulse and short $(\sim 1\mathrm{ps})$ second, it is shown that effective high-gain systems may be developed.

The generation of macroscopic and spatially separated three-mode entangled light for triply coupled ${\chi }^{\left(3\right)}$ Kerr coupler inside a pumped optical cavity is investigated. With the linearized analysis for small perturbation around the steady state of the pumped cavity modes, the linearized Hamiltonian and the corresponding master equation are obtained. It is found that the bright three-mode squeezing and full inseparable entanglement can be achieved both inside and outside the cavity.

We present a theoretical study of the curvature-induced radiation of surface plasmon polaritons propagating around bends at metal-dielectric interfaces. We explain qualitatively how the curvature leads to distortion of the phase front, causing the fields to radiate energy away from the metal-dielectric interface. We then quantify, both analytically and numerically, radiation losses and energy transmission efficiencies of surface plasmon polaritons propagating around bends with varying radii as well as sign of curvature.

We have found that xenon in different charge states, namely, ${\mathrm{Xe}}^{9+}$ and ${\mathrm{Xe}}^{31+}$, can contribute to the radiation in the $598\mathrm{nm}$ spectral range. Our observation resolves the discrepancy of line identification given by Takács et al. [Phys. Rev. A 73, 052505 (2006)] and Crespo et al. [Can. J. Phys. 80, 1687 (2002)].

The coherent bit (cobit) channel is a resource intermediate between classical and quantum communication. It produces coherent versions of teleportation and superdense coding. We extend the cobit channel to continuous variables by providing a definition of the coherent nat (conat) channel. We construct several coherent protocols that use both a position-quadrature and a momentum-quadrature conat channel with finite squeezing. Finally, we show that the quality of squeezing diminishes through successive compositions of coherent teleportation and superdense coding.

The transport properties of a Bose-Einstein condensate in a 1D incommensurate bichromatic lattice are investigated both theoretically and experimentally. We observe a blockage of the center of mass motion with low atom number, and a return of motion when the atom number is increased. Solutions of the Gross-Pitaevskii equation show how the localization due to the quasidisorder introduced by the incommensurate bichromatic lattice is affected by the interactions.

We quantitatively analyze the dynamics of the quantum phase distribution associated with the reduced density matrix of a system, as the system evolves under the influence of its environment with an energy-preserving quantum nondemolition (QND) type of coupling. We take the system to be either an oscillator (harmonic or anharmonic) or a two-level atom (or equivalently, a spin-1/2 system), and model the environment as a bath of harmonic oscillators, initially in a general squeezed thermal state. The impact of the different environmental parameters is explicitly brought out as the system starts out in various initial states. The results are applicable to a variety of physical systems now studied experimentally with QND measurements.

We study how the entanglement between two atoms can be created or modified even when they do not interact but when each of them interacts dispersively, i.e., weak and far from the resonance, with a single mode of the field. In particular, we study two cases: First we consider each atom to be initially in a pure state and secondly we assume that they start in a Werner state. Analytically we find that both atoms can, periodically, reach maximum entanglement if each of them starts in any state belonging to the Bloch sphere equator, independent of the initial Fock state of the mode. Thus, in particular, we find that a dispersive vacuum mode can generate entanglement between two two-level atoms. In the second case, when the field mode is initially in a coherent or thermal state we find that, in the high energy limit, in general there is no entanglement between the two atoms. However, at well defined moments, the initial entanglement appears and disappears suddenly, becoming a narrow entanglement-beats structure.

We propose an entanglement measure for two quNits based on the covariances of a set of generators of the $\mathrm{su}\left(N\right)$ algebra. In particular, we represent this measure in terms of the mutually unbiased projectors for $N$ prime. For pure states this measure quantifies entanglement, we obtain an explicit expression which relates it to the concurrence hierarchy, specifically the $I$-concurrence and the three-concurrence. For mixed states we propose a separability criterion.

Electron and positron cross sections for scattering from toluene molecules have been investigated both experimentally and theoretically over the energy range $0.4–1000\mathrm{eV}$. Peaks have been observed in the electron total cross sections (TCSs) at 1.4, 4.5, and 8.0 and a shoulder at about $40\mathrm{eV}$. Vibrational and elastic differential cross section experiments were carried out to probe the origin and nature of these peaks. The continuum multiple scattering method was used to calculate elastic integral cross sections for electron impact. Although the $1.4\mathrm{eV}$ peak is dominated by the elastic channel, strong contributions from the ${\mathrm{CH}}_3$ asymmetric bending and stretching vibrational modes are also observed. The $4.5\mathrm{eV}$ feature is also observed to be strongly due to vibrational excitation. The broad $7–13\mathrm{eV}$ peak includes contributions from the ${\mathrm{CH}}_3$ asymmetric bending (peaked at $7\mathrm{eV}$) and the ${\mathrm{CH}}_3$ stretching (peaked at $9.5\mathrm{eV}$) vibrational modes. Positron TCSs are studied and compared to positron-benzene TCSs. The effect of the ${\mathrm{CH}}_3$ substitution is observed to make a significant contribution to both electron and positron TCSs below $20\mathrm{eV}$.

A gauge invariant formulation of the so-called intense-field Keldysh-Faisal-Reiss (KFR) approximations in the “velocity” and “length” gauges is given and their equivalence is demonstrated term by term to all orders of the theory. It overcomes a long standing discrepancy between the velocity and the length gauge strong-field KFR amplitudes for nonperturbative processes in intense laser fields.

A rotating bosonic many-body system in a harmonic trap is studied with the three-dimensional cranked Hartree-Fock-Bogoliubov method at zero temperature, which has been applied to nuclear many-body systems at high spin. This method is a variational method extended from Hartree-Fock theory, which can treat the pairing correlations in a self-consistent manner. An advantage of this method is that a finite-range interaction between constituent particles can be used in the calculation, unlike the original Gross-Pitaevskii approach. To demonstrate the validity of our method, we present a calculation for a toy model—that is, a rotating system of ten bosonic particles interacting through the repulsive quadrupole-quadrupole interaction in a harmonic trap. It is found that the yrast states, the lowest-energy states for the given total angular momentum, do not correspond to the Bose-Einstein condensate, except for a few special cases. One such case is a vortex state, which appears when the total angular momentum $L$ is twice the particle number $N$ (i.e., $L=2N$).

We present a scheme to conditionally generate an arbitrary superposition of a pair of coherent states from a squeezed vacuum by means of the modified photon subtraction where a coherent state ancilla and two on/off type detectors are used. We show that, even including realistic imperfections of the detectors, our scheme can generate a target state with a high fidelity. The amplitude of the generated states can be amplified by conditional homodyne detections.

We investigate localization of the entanglement of multimode Gaussian states into a pair of modes by local Gaussian measurements on the remaining modes and classical communication. We find that for pure states and for mixed symmetric states maximum entanglement between two modes can be localized by local homodyne detection—i.e. projections onto infinitely squeezed states. We also show that non-Gaussian measurements allow us to localize more entanglement than Gaussian ones.

High-resolution electron-ion coincidence spectroscopy is used to (i) map correlations between electrons and ions from atomlike ionization of ethanol by intense 400 and $800\mathrm{nm}$ light pulses and (ii) disentangle the effects of dissociative multiphoton (MPI) and tunneling (TI) ionization. Electron spectra correlated with ${\mathrm{C}}^{n+}$ $(n=1,2,3)$ exhibit a continuum structure with a high-energy tail due to inelastic collisions involving rescattered electrons following TI, while those correlated with ${\mathrm{C}}_2{\mathrm{H}}_n{\mathrm{O}}^{+}$ have structure characteristic of MPI and above-threshold ionization.

We analyze photon scattering by a harmonically trapped ion using two-port interferometry of the scattered photon and coherent-state measurement of the ion’s external recoil motion. We examine how the coherent-state measurement could be used to mimick both momentum and position ion measurements and thus a modern realization of Wootters and Zurek’s pioneering analysis of Einstein’s historic recoiling-slit gedanken experiment. To quantify the photon-path which-port information cached in the recoiling ion and the underlying wave-particle duality, we evaluate the ion-state trace distance and distinguishability.

We study the amount of interference in random quantum algorithms using a recently derived quantitative measure of interference. To this end we introduce two random circuit ensembles composed of random sequences of quantum gates from a universal set, mimicking quantum algorithms in the quantum circuit representation. We show numerically that, concerning the interference distribution and the level spacing distribution, these ensembles converge to the well-known circular unitary ensemble (CUE) for general complex quantum algorithms, and to the Haar orthogonal ensemble (HOE) for real quantum algorithms. We provide exact analytical formulas for the average and typical interference in the circular ensembles, and show that for sufficiently large numbers of qubits a random quantum algorithm uses with probability close to one an amount of interference approximately equal to the dimension of the Hilbert space. As a by-product, we offer a new way of constructing approximate random unitary operators from the Haar measures of CUE or HOE in a high dimensional Hilbert space using universal sets of quantum gates.

We work out a theory of approximate quantum error correction that allows us to derive a general lower bound for the entanglement fidelity of a quantum code. The lower bound is given in terms of Kraus operators of the quantum noise. This result is then used to analyze the average error correcting performance of codes that are randomly drawn from unitarily invariant code ensembles. Our results confirm that random codes of sufficiently large block size are highly suitable for quantum error correction. Moreover, employing a lemma of Bennett, Shor, Smolin, and Thapliyal, we prove that random coding attains information rates of the regularized coherent information.

Two interacting electrons that are confined to the surface of a sphere have a uniform ground-state (surface) density. The Schrödinger equation of this helium-type two-electron system is solved here accurately for different values $\alpha ∊\mathbb{R}$ of a constant that is multiplied to the electron-electron repulsion ${\widehat{V}}_{\mathit{ee}}$. The correlation structure in the resulting wave functions is analyzed for different values of $\alpha$. The asymptotic limits $\alpha \to 0$ and $\alpha \to \pm \infty$ are treated analytically. Using these results, the ISI (interaction-strength interpolation) model for the density-functional $E_{\mathit{xc}}\left[\rho \right]$ of the exchange-correlation energy in the real system with $\alpha =1$ is tested against the exact adiabatic connection in density-functional theory.