We discuss some properties of the Knill-Laflamme-Milburn scheme for quantum teleportation with both maximally and nonmaximally entangled states. We derive the error correction scheme when one performs teleportation with nonmaximally entangled states and we find the probability for perfect teleportation. We show that the maximally entangled state is optimal in such a case. We also show how the error correction scheme can be implemented experimentally when one uses polarization encoding.

In a recent Letter [], four protocols were proposed to secretly transmit a reference frame. Here we point out that in these protocols an eavesdropper can change the transmitted reference frame without being detected, which means the consistency of the shared reference frames should be reexamined. The way to check the above consistency is discussed. It is shown that this problem is quite different from that in previous protocols of quantum cryptography.

A scheme is proposed for the deterministic generation of three-dimensional entanglement of two distant atoms separately trapped in two optical cavities connected by an optical fiber. Employing adiabatic passage along dark states, the atoms are always in ground states, in particular, the fiber mode remains in the vacuum state due to the quantum destructive interference, and the population of the cavities being excited can be negligible under certain conditions. In this sense, our scheme constructs an effective way to avoid the atomic spontaneous emission and the decays of fiber and cavities.

It is theoretically shown that the spectrum of a frequency mode-locked laser with an intracavity dielectric plate, which modulates the cavity axial mode resonances, can undergo a kind of metal-insulator transition analogous to that encountered in the incommensurate Harper model of solid-state physics. The transition should be observable as a rather abrupt spectral broadening of the laser emission, accompanied by a transition from exponential to Gaussian spectral localization, as the modulation depth is increased above a threshold value.

We consider the dynamical Casimir effect for a massless scalar field in a two-dimensional space-time, inside an oscillating cavity with mixed boundary conditions. We obtain the energy-momentum tensor for this model, verifying the occurrence of traveling wave packets for the energy density and also studying the time evolution of the total energy stored in the cavity. We compare our results with those found in the literature for the Dirichlet-Dirichlet case.

We calculate the joint probabilities and the correlation function in Einstein-Podolsky-Rosen–type experiments with a massive vector boson in the framework of quantum field theory. We report on the strange behavior of the correlation function (and the probabilities)—the correlation function, which in the relativistic case still depends on the particle momenta, for some fixed configurations has local extrema. We also show that relativistic spin-1 particles violate some Bell inequalities more than nonrelativistic ones and that the degree of violation of the Bell inequality is momentum dependent.

By means of the density matrix renormalization group technique, the scaling relation of the fidelity susceptibility proposed recently is verified for the spin-one $XXZ$ spin chain with an on-site anisotropic term. Moreover, from the results of both the fidelity susceptibility and the entanglement entropy, the critical points and some of the corresponding critical exponents are determined through a proper finite-size scaling analysis, and these values agree with the findings in the literature. Thus our work provides a numerical support of the use of the fidelity in detecting quantum phase transitions.

Variational methods to treat a many-electron system embedded in the environment, which is represented by means of only its electron density, are considered. It is shown that the embedding operator is a local potential in the case where the electron-electron repulsion is treated exactly and the trial embedded wave function takes the multideterminantal form with a fixed number of determinants. The local embedding potential is constructed by imposing that it leads to the same electron density as the one which minimizes the Hohenberg-Kohn functional. For the limiting cases of single-determinant and configuration interaction forms of the embedded wave function, the expressions for the local embedding potential using commonly known density functionals are given. The relation between the derived local embedding potential and the effective embedding potential in the case of the embedded Kohn-Sham system [T. A. Wesołowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993)] is discussed in detail.

Integrals of the two-body scattering $T\left(r,r^{\prime }\right)$ matrix over an arbitrary function $\Phi \left(r^{\prime }\right)$ are carried out in configuration space. The method consists of representing these integrals $\phi \left(r\right)$ as the solution of a one-variable Lippmann-Schwinger integral equation, and numerically obtaining the solution by a spectral expansion method that is very similar to a previously developed method [the spectral integral equation method (S-IEM)] for obtaining the wave function of a Schrödinger equation. It is found that the desirable features of the S-IEM, such as the economy of mesh points for a given required accuracy, are carried over also to this case. Stability to eight significant figures is achieved in a MATLAB code that takes 1/3 s for its execution, using as a value of ${10}^{-8}$ for an inputted tolerance parameter. The importance of correctly treating the repulsive core for the atomic He-He interaction is demonstrated.

We develop a semiclassical quasistatic model accounting for molecular double ionization in an intense laser pulse. With this model, we achieve insight into the dynamics of two highly-correlated valence electrons under the combined influence of a two-center Coulomb potential and an intense laser field, and reveal the significant influence of molecular alignment on the ratio of double- over single-ion yield. Analysis of the classical trajectories unveils subcycle dynamics of the molecular double ionization. Many interesting features, such as the accumulation of emitted electrons in the first and third quadrants of the parallel-momentum plane and the regular pattern of correlated momentum with respect to the time delay between the closest collision and ionization moment, are revealed and successfully explained by back-analyzing the classical trajectories. Quantitative agreement with experimental data over a wide range of laser intensities from the tunneling to the over-the-barrier regime is presented.

Possible signatures are discussed of a super-Tonks-Girardeau gas in bosonic systems of trapped quasi-one-dimensional dipoles at zero temperature. We provide an estimation of the frequency of the lowest compressional mode and compare it to analytical results derived using the harmonic approach in the high-density regime. We construct an exact mapping of the ground-state wave function of a one-dimensional dipolar system of bosons, fermions, and a Bose-Fermi mixture and conclude that the local properties and energy are the same at zero temperature. The question as to what extent the dipolar potential can be treated as long or short range is discussed.

High-order harmonic generation (HHG) in a near infrared driving laser pulse by mixing a weak ultraviolet pulse is investigated and a different concept of attosecond temporal filter is proposed. We show that this temporal filter can be used to (i) select the specific high-order harmonics that one wants, (ii) image the HHG and quantum trajectories in the real-time–frequency domain, and (iii) determine the carrier-envelope phase of the driving laser pulse.

We study the electromagnetic surface waves localized at an interface separating a homogeneous dielectric medium and a semi-infinite one-dimensional photonic crystal made of alternative left-handed metamaterial and right-handed material. An analytical direct matching procedure within the Kronig-Penney model was applied to analyze the dispersion properties of the localized surface states. We show that the presence of metamaterial in the photonic crystal structure can support the surface waves with a backward energy flow and allows a flexible control of dispersion properties of the surface modes. The surface states can be either forward or backward waves depending on the physical parameters of the photonic crystal, physical parameters of the cap layer, the position of the surface plane, and incident angle of the incoming beam.

We have numerically solved the Heisenberg-Langevin equations describing the propagation of quantized fields through an optically thick sample of atoms. Two orthogonal polarization components are considered for the field, and the complete Zeeman sublevel structure of the atomic transition is taken into account. Quantum fluctuations of atomic operators are included through appropriate Langevin forces. We have considered an incident field in a linearly polarized coherent state (driving field) and vacuum in the perpendicular polarization and calculated the noise spectra of the amplitude and phase quadratures of the output field for two orthogonal polarizations. We analyze different configurations depending on the total angular momentum of the ground and excited atomic states. We examine the generation of squeezing for the driving-field polarization component and vacuum squeezing of the orthogonal polarization. Entanglement of orthogonally polarized modes is predicted. Noise spectral features specific to (Zeeman) multilevel configurations are identified.

The metamaterials exhibiting negative permittivity and permeability that have been under numerical and experimental study recently generally operate at frequencies between the homogeneous $\left(\lambda \gg \text{period}\right)$ and heterogeneous $\left(\lambda \approx \text{period}\right)$ regimes, a region characterized by the phenomenon of spatial dispersion. However, since many interesting applications such as the superlens rely on nondispersive homogeneous behavior, one needs a means to diagnose spatial dispersion efficiently as well as to explore in more detail the physics of dispersive media. In this work, we put forward and illustrate the notion of an inhomogeneous effective medium model. We use it to explore the spatial dispersion in negative-index composites, and we show that it is an ideal tool for studying the behavior of composite metamaterials in the intermediate-frequency region where homogeneous effective medium models become spatially dispersive or nonlocal.

A possible two-qubit gate for optical quantum computing is the parity gate based on the weak Kerr effect. Two photonic qubits modulate the phase of a coherent state, and a quadrature measurement of the coherent state reveals the parity of the two qubits without destroying the photons. This can be used to create so-called cluster states, a universal resource for quantum computing. Here, the effect of self-phase modulation on the parity gate is studied, introducing generating functions for the Wigner function of a modulated coherent state. For materials with non-electromagnetically-induced-transparency-based Kerr nonlinearities, there is typically a self-phase modulation that is half the magnitude of the cross-phase modulation. Therefore, this effect cannot be ignored. It is shown that for a large class of physical implementations of the phase modulation, the quadrature measurement cannot distinguish between odd and even parity. Consequently, weak nonlinear parity gates must be implemented with physical systems where the self-phase modulation is negligible.

Time-dependent lattice methods in both Cartesian and cylindrical coordinates are applied to calculate excitation cross sections for $p+\mathrm{H}$ collisions at $40\mathrm{keV}$ incident energy. The time-dependent Schrödinger equation is solved using a previously formulated Cartesian coordinate single-channel method on a full 3D lattice and a newly formulated cylindrical coordinate multichannel method on a set of coupled 2D lattices. Cartesian coordinate single-channel and cylindrical coordinate five-channel calculations are found to be in reasonable agreement for excitation cross sections from the $1s$ ground state to the $2s$, $2p$, $3s$, $3p$, and $3d$ excited states. For extension of the time-dependent lattice method to handle the two electron dynamics found in $p+\mathrm{He}$ collisions, the cylindrical coordinate multichannel method appears promising due to the reduced dimensionality of its lattice.

We show that the angular spectrum of type-II SPDC contains a continuum of maximally entangled states. For the realization of a bright source of entangled two-photon states, a standard technique is to compensate for the transverse walkoff in the production crystal. We demonstrate that polarization entangled states can be effectively engineered by generalizing this approach. Our method allows us to considerably enrich the set of generated entangled states with a controlled tailoring of them.

We theoretically discuss spontaneous emission properties of a quantum dot embedded in an ultrahigh-$Q$ microcavity, where a detuning between an excitation in the quantum dot and the cavity mode is taken into account. Both weak- and strong-coupling states are obtained under the ultrahigh-$Q$ condition. In the high-$Q$ weak-coupling case, the spontaneous emission spectrum shows a sharp dip, whose origin is a quantum interference. In the strong-coupling case, there is a region where both the Rabi splitting and the quantum interference contribute on an equal footing, referred to as a crossover region, where the spontaneous emission spectral shape is quite similar to that of the high-$Q$ weak-coupling state. The quantum interference is robust against the detuning.

We construct a family of quantum maximum-distance-separable (MDS) codes from classical generalized Reed-Solomon codes and derive the necessary and sufficient condition under which these quantum codes exist. We also give code bounds and show how to construct them analytically. We find that existing quantum MDS codes can be unified under these codes in the sense that when a quantum MDS code exists, then a quantum code of this type with the same parameters also exists. Thus, as far as is known at present, they are the most important family of quantum MDS codes.