We quantify noise-induced phase deviations of dispersion-managed solitons (DMS) in optical fiber communications and femtosecond lasers. We first develop a perturbation theory for the dispersion-managed nonlinear Schrödinger equation (DMNLSE) in order to compute the noise-induced mean and variance of the soliton parameters. We then use the analytical results to guide importance-sampled Monte Carlo simulations of the noise-driven DMNLSE. Comparison of these results with those from the original unaveraged governing equations confirms the validity of the DMNLSE as a model for many dispersion-managed systems and quantify the increased robustness of DMS with respect to noise-induced phase jitter.

We present a method for controlling the spatial properties of a high-order harmonic beam on a subcycle time scale. By adding a second-harmonic field to the driving laser field, we modify the spatiotemporal structure of the harmonic beam and manipulate it with attosecond resolution. Such a manipulation maps the subcycle dynamics of a recolliding electron to the spatial domain.

We investigate the entanglement between two spatially separated intervals in the vacuum state of a free one-dimensional Klein-Gordon field by means of explicit computations in the continuum limit of the linear harmonic chain. We demonstrate that the entanglement, which we quantify by the logarithmic negativity, is finite with no further need for renormalization. We find that in the critical regime, the quantum correlations are scale invariant as they depend only on the ratio of distance to length. They decay much faster than the classical correlations as in the critical limit long-range entanglement decays exponentially for separations larger than the size of the blocks, while classical correlations follow a power-law decay. With decreasing distance of the blocks, the entanglement diverges as a power law in the distance. The noncritical regime manifests richer behavior, as the entanglement depends both on the size of the blocks and on their separation. In correspondence with the von Neumann entropy also long-range entanglement distinguishes critical from noncritical systems.

We formulate the theory of three-body scattering without explicit reference to exact asymptotic boundary conditions on the wave function. The transition rate and amplitude are expressed as volume integrals of the resolvent, which are insensitive to the region of asymptotically large distances. The physical branch of the resolvent is selected through the arrow of time, which is required to point forward in each subchannel. This is accomplished by first expressing the resolvent as an integral over time and then making a conformal transformation of each half of the time plane onto a unit disk. The physical branch corresponds to a path of integration in the upper half of the disk. We have tested the method, using a real discrete basis, by calculating the total cross section for singlet $S$-wave electron impact ionization of atomic hydrogen; our results are in reasonable agreement overall with the landmark results of Bartlet and Stelbovics [Phys. Rev. Lett. 93, 233201 (2004)].

We investigate the coherent control of a single particle held in a quartic double well with a symmetric or asymmetric driving and exhibit time evolutions of relative probability of the particle in one of the double-well wells. It is shown analytically and numerically that the coherent destruction of tunneling could occur only for the symmetric intense driving, and application of the asymmetric sawtooth driving leads to an increase in the tunneling rate. The results agree with the recent experimental data reported by Kierig et al. [Phys. Rev. Lett. 100, 190405 (2008)]. We also exhibit the effect of multiple photon resonances on the tunneling through a dc field. Finally, we demonstrate a connection between the classically chaotic barrier crossing and quantum tunneling numerically.

We study statistical signatures of composite bosons made of two fermions by extending number states to these quantum particles. Two-particle correlations as well as the dispersion of the probability distribution are analyzed. We show that the particle composite nature reduces the antibunching effect predicted for elementary bosons. Furthermore, the probability distribution exhibits a dispersion that is greater for composite bosons than for elementary bosons. This dispersion corresponds to the one of sub-Poissonian processes, as for a quantum state but, unlike its elementary boson counterpart, it is not minimum. In general, our work shows that it is necessary to take into account the Pauli exclusion principle, which acts between fermionic components of composite bosons—along the line used here—to possibly extract statistical properties in a precise way.

We study the light dispersion relation in a periodic ensemble of atoms at fixed positions in the Fano-Hopfield model (the atomic dipole being modeled with harmonic oscillators). Compared to earlier works, we do not restrict to cubic lattices, and we do not regularize the theory by hand but we renormalize it in a systematic way using a Gaussian cutoff in momentum space. Whereas no omnidirectional spectral gap is known for light in a Bravais atomic lattice, we find that, for a wide range of parameters, an omnidirectional gap occurs in a diamond atomic lattice, which may be realized in an experiment with ultracold atoms. The long-wavelength limit of the theory also provides a Lorentz-Lorenz (or Clausius-Mossotti) relation for an arbitrary lattice.

We present a strategy to achieve carrier-envelope phase-dependent field-free molecular orientation with the use of carrier-envelope phase (CEP) stabilization and asymmetric few-cycle terahertz (THz) laser pulses. The calculations are performed on the LiH molecule by an exact solution of the full time-dependent Schrödinger equation including both the vibrational and the rotational degrees of freedom. Our calculations show that an efficient field-free molecular orientation can be obtained even at considerable temperatures. Moreover, we find a simple dependence of the field-free orientation on the CEP, which implies that the CEP becomes an important parameter for control of molecular orientation. More importantly, the realization of this scenario is appealing based on the fact that the intense few-cycle THz pulse with duration as short as a few optical cycles is available as a research tool.

The thermal pairwise entanglement (TE) of the $S=1/2$ $XY$ chain in a transverse magnetic field is exactly resolved by means of the Jordan-Wigner transformation in the thermodynamic limit $N\to \infty$. It is found that the TE vanishes at a fixed point with temperature $T_c\simeq 0.4843J$, which is independent of the magnetic field. A thermal quantity is proposed to witness the entangled state. Furthermore, the TE of the $S=1/2$ antiferromagnetic-ferromagnetic (AF-F) Heisenberg chain is studied by the transfer-matrix renormalization-group method. The TEs of the spins coupled by AF and F interactions are found to behave distinctively. The vanishing temperature of the field-induced TE of the spins coupled by F interactions is observed dependent on the magnetic field. The results are further confirmed and analyzed within a mean-field framework.

While quantum entanglement is known to be monogamous (i.e., shared entanglement is restricted in multipartite settings), here we show that distributed entanglement (or the potential for entanglement) is by nature polygamous. By establishing the concept of one-way unlocalizable entanglement (UE) and investigating its properties, we provide a polygamy inequality of distributed entanglement in tripartite quantum systems of arbitrary dimension. We also provide a polygamy inequality in multiqubit systems and several trade-offs between UE and other correlation measures.

The fragmentation of the hydronium cation ${\text{H}}_3{\text{O}}^{+}$ after photoabsorption at 13.5 nm has been investigated with a crossed-photon-and-ion-beams experiment making pulsing and trapping techniques available for fragment momentum imaging at the intense Free-electron LASer in Hamburg. The observed photofragmentation patterns demonstrate that the photolysis of ${\text{H}}_3{\text{O}}^{+}$ proceeds by valence ionization into ${\text{H}}_3{\text{O}}^{2+}$ which subsequently fragments to mainly $\text{OH}+2{\text{H}}^{+}$ and ${\text{H}}_2{\text{O}}^{+}+{\text{H}}^{+}$ with a branching ratio of up to 0.6:1 and with different degrees of excitation of the molecular fragment. The cross section for fragmentation into $\text{OH}+2{\text{H}}^{+}$ is found to be $\left(0.37\pm 0.18\right)\times {10}^{-18}{\text{cm}}^2$, while the total photoabsorption cross section is estimated to be greater than $0.95\times {10}^{-18}{\text{cm}}^2$. The data suggest that ionization mainly occurs from the $3a_1$ and $1e$ valence orbitals and that initial ionization from $3a_1$ mainly leads to fragmentation into ${\text{H}}_2{\text{O}}^{+}\left(A{{}^{2}A}_1\right)+{\text{H}}^{+}$ while initial ionization from the $1e$ orbital predominantly populates the ${\text{H}}_2{\text{O}}^{+}\left(B{{}^{2}B}_2\right)+{\text{H}}^{+}$ and $\text{OH}\left(X{}^2\Pi \right)+2{\text{H}}^{+}$ channels. The results are of significance for astrophysical models of gas clouds in the vicinity of hot radiating objects and for models of the chemistry of planetary and lunar ionospheres under solar irradiation.

We demonstrate a two-dimensional magneto-optical trap (2D MOT) as a beam source for cold ${}^6\text{L}\text{i}$ atoms. The source is side loaded from an oven operated at temperatures in the range $600\lesssim T\lesssim 700\text{K}$. The performance is analyzed by loading the atoms into a three-dimensional MOT located 220 mm downstream from the source. The maximum recapture rate of $\sim {10}^9{\text{s}}^{-1}$ is obtained for $T\approx 700\text{K}$ and results in a total of up to ${10}^{10}$ trapped atoms. The recaptured fraction is estimated to be $30\pm 10\%$ and limited by beam divergence. The most-probable velocity in the beam $\left({\alpha }_z\right)$ is varied from 18 to 70 m/s by increasing the intensity of a push beam. The source is quite monochromatic with a full width at half maximum velocity spread of 11 m/s at ${\alpha }_z=36\text{m}/\text{s}$, demonstrating that side loading completely eliminates beam contamination by hot vapor from the oven. We identify depletion of the low-velocity tail of the oven flux as the limiting loss mechanism. Our approach is suitable for other atomic species.

We examine the spontaneous breakdown of the matter vacuum triggered by an external force of arbitrary strength and spatial and temporal variations. We derive a nonperturbative framework that permits the computation of the complete time evolution of various multiple electron-positron pair probabilities. These time-dependent probabilities can be computed from a generating function as well as from solutions to a set of ratelike equations with coupling constants determined by the single-particle solutions to the time-dependent Dirac equation. This approach might be of relevance to the planned experiments to observe for the first time the laser-induced breakdown process of the vacuum.

Strong one-dimensional (1D) lattices usually lead to unconnected two-dimensional gases. The long-range character of the dipole-dipole interactions leads to a scenario where nonoverlapping gases at different sites may interact significantly. We show that the excitations of nonoverlapping condensates in 1D optical lattices acquire a bandlike character, being collectively shared by different sites. In particular, the hybridization of the modes significantly enhances the rotonization of the excitations and may induce roton instability. We discuss the observability of this effect in ongoing experiments.

We propose a technique to obtain slow and fast light propagations based on coherent population oscillations forced by a modulated pump. This mechanism produces an enhancement of 1 order of magnitude of the delay or advancement of light signals. The relative phase between the pumps to the signal fields is used as a knob for changing light propagation from ultraslow group velocities to negative group velocities. The experimental realization of the phenomenon was carried out in an erbium-doped fiber amplifier at room temperature.

Fisher information, which lies at the heart of parameter estimation theory, was recently found to have a close relation with multipartite entanglement [L. Pezzé and A. Smerzi, Phys. Rev. Lett. 102, 100401 (2009)]. We use Fisher information to distinguish and characterize behaviors of ground state of the Lipkin-Meskhov-Glick model, which displays a second-order quantum phase transition between the broken and symmetric phases. We find that the parameter sensitivity of the system attains the Heisenberg limit in the broken phase, while it is just around the shot-noise limit in the symmetric phase. Based on parameter estimation, Fisher information provides us a useful approach to the quantum phase transition.

We prove that the most general $W$ class of $N$-qubit states are uniquely determined among arbitrary states (pure or mixed) by just their bipartite reduced density matrices. Moreover, if we consider only pure states, then $\left(N-1\right)$ of them are shown to be sufficient.

We propose a scenario of quantum memory for light based on Raman scattering. The storage medium is a vapor and the different spectral components of the input pulse are stored in different atomic velocity classes. One uses appropriate pulses to reverse the resulting Doppler phase shift and to regenerate the input pulse, without distortion, in the backward direction. The different stages of the protocol are detailed and the recovery efficiency is calculated in the semiclassical picture. Since the memory bandwidth is determined by the Raman transition Doppler width, it can be adjusted by changing the angle between the input pulse wave vector and the control beams. The optical depth also depends on the beam angle. As a consequence the available optical depth can be optimized depending on the needed bandwidth. The predicted recovery efficiency is close to 100% for large optical depth.

In this work the topological order at finite temperature in two-dimensional color code is studied. The topological entropy is used to measure the behavior of the topological order. Topological order in color code arises from the colored string-net structures. By imposing the hard constrained limit the exact solution of the entanglement entropy becomes possible. For finite size systems, by raising the temperature, one type of string-net structure is thermalized and the associative topological entropy vanishes. In the thermodynamic limit the underlying topological order is fragile even at very low temperatures. Taking first the thermodynamic limit and then the zero-temperature limit and vice versa does not commute, and their difference is related only to the topology of regions. The contribution of the colors and symmetry of the model in the topological entropy is also discussed. It is shown how the gauge symmetry of the color code underlies the topological entropy.

Recently Sagawa and Ueda [Phys. Rev. Lett. 100, 080403 (2008)] derived a bound on the work that can be extracted from a quantum system with the use of feedback control. For many quantum measurements their bound was not tight. We show that a tight version of this bound follows straightforwardly from recent work on Maxwell’s demon by Alicki et al. [Open Syst. Inf. Dyn. 11, 205 (2004)], for both discrete and continuous feedback control. Our analysis also shows that bare, efficient measurements always do non-negative work on a system in equilibrium, but do not add heat.