We study the transmission of a monochromatic “image” through a paraxial cavity. Using the formalism of self-transform functions, we show that a transverse degenerate cavity transmits the self-transform part of the image, with respect to the field transformation over one round-trip of the cavity. This formalism gives insight into the understanding of the behavior of a transverse degenerate cavity, complementary to the transverse mode picture. An experiment of image transmission through a hemiconfocal cavity shows the interest of this approach.

Even harmonic molecules display a nonlinear behavior when driven by an inhomogeneous field. We calculate the response of single harmonic molecules to a monochromatic time and space dependent electric field $E(r,t)$ of frequency $\omega$ employing exact algebraic methods. We evaluate the responses at the fundamental frequency $\omega$ and at successive harmonics $2\omega$, $3\omega$, etc., as a function of the intensity and of the frequency of the field and compare the results with those of first and second order perturbation theory.

We investigate the security of continuous-variable (CV) quantum key distribution (QKD) using coherent states in the presence of quadrature excess noise. We consider an eavesdropping attack that uses a linear amplifier and a beam splitter. This attack makes a link between the beam-splitting attack and the intercept-resend attack (classical teleportation attack). We also show how postselection loses its efficiency in a realistic channel.

In this Comment we present a counterexample to theorems 2 and 3 from Chau [Phys. Rev. A 58, 905 (1998)] regarding quantum convolutional codes.

In their Comment, ] discovered an error in my earlier paper concerning the construction of quantum convolutional codes []. This error can be repaired by modifying the method of code construction.

Currently there is no accurate theoretical approach available for treating fully differential cross sections (FDCS) for low-energy electron-impact ionization of large molecules. For high incident energies, the plane wave impulse approximation (PWIA) generally yields good agreement with experimental data. In this paper, the distorted wave impulse approximation (DWIA) is used to calculate FDCS for low-energy electron-impact ionization of ${\mathrm{N}}_2$. To perform the necessary average over all molecular orientations, we propose an orientation average (OA) approximation. Although the DWIA results represent an improvement over the PWIA for intermediate energies, an improved theory is necessary for lower energies. However, the OA approximation will greatly simplify the evaluation of improved theories for lower energies.

The vacuum energy between two birefringent plates was calculated using the quantized surface mode technique. And an analytical approximate expression of Casimir torque was obtained in the retarded limit, which is found to vary as $\sin \left(2\phi \right)$ with $\phi$, the angle between the two optical axes. This result is a supplement to the numerical calculation obtained by Munday, Iannuzzi, Barash, and Capasso [Phys. Rev. A. 71, 042102 (2005)].

A multiparty quantum secret sharing (QSS) protocol of classical messages (i.e., classical bits) is proposed by using swapping quantum entanglement of Bell states. The secret messages are imposed on Bell states by local unitary operations. The secret messages are split into several parts, and each part is distributed to a separate party so that no action of a subset of all the parties without the cooperation of the entire group is able to read out the secret messages. In addition, dense coding is used in this protocol to achieve a high efficiency. The security of the present multiparty QSS against eavesdropping has been analyzed and confirmed even in a noisy quantum channel.

Communicating a physical quantity cannot be done using information only—i.e., using abstract cbits and∕or qubits. Rather one needs appropriate physical realizations of cbits and∕or qubits. We illustrate this by considering the problem of communicating chirality. We discuss in detail the physical resources this necessitates and introduce the natural concept of quantum gloves—i.e., rotationally invariant quantum states that encode as much as possible the concept of chirality and nothing more.

The ionization process due to collision of ${\mathrm{He}}^{2+}$ with ${\mathrm{C}}^{5+}\left(1s\right)$ is investigated using a continuum-distorted-wave eikonal-initial-state approximation. Total, single-, and double-differential cross sections are presented for collision energies from $30\mathrm{keV}∕\mathrm{u}$ to $10\mathrm{MeV}∕\mathrm{u}$. A good agreement is obtained between the current total cross section and the previous predictions. The ionization mechanism of electron capture to the projectile continuum (ECC) is found to be important in the lower collision energy range, whose contributions to the total cross section are evaluated to be approximately 12, 9, and 7 % for the projectile energies of $125\mathrm{keV}∕\mathrm{u},500\mathrm{keV}∕\mathrm{u}$, and $1\mathrm{MeV}∕\mathrm{u}$ respectively. These large ECC contributions could be interpreted by the velocity matching between the projectile ion and the electron initially bound to the target.

The light-induced force on an atom is calculated for an arbitrary field configuration, taking into account the spontaneous emission and optical pumping processes as well as the degeneracy of atomic energy levels. Two types of the optical transitions are analyzed: $J\to J$ with $J$ a half-integer and $J\to J+1$ with $J$ an arbitrary. Though the force is not potential in the general case, we introduce a scalar function $\Psi$, which plays a role of the potential energy, determining regions of localization of atoms. Applications of these results to atom nanolithography are discussed.

We extend our earlier work on the nonequilibrium dynamics of a Bose-Einstein condensate initially loaded into a one-dimensional optical lattice. From the two-particle-irreducible (2PI) closed-time-path (CTP) effective action for the Bose-Hubbard Hamiltonian we derive causal equations of motion that treat mean-field effects and quantum fluctuations on an equal footing. We demonstrate that these equations reproduce well-known limits when simplifying approximations are introduced. For example, when the system dynamics admits two-time separation, we obtain the Kadanoff-Baym equations of quantum kinetic theory, and in the weakly interacting limit, we show that the local equilibrium solutions of our equations reproduce the second-order corrections to the self-energy of the type originally derived by Beliaev. The derivation of quantum kinetic equations from the 2PI-CTP effective action not only checks the viability of the formalism but also shows it to be a tractable framework for going beyond standard Boltzmann equations of motion.

We study the spontaneous-emission properties of a coherently driven four-level atom, and show a few interesting phenomena such as fluorescence quenching, spectral-line narrowing, spectral-line enhancement, and spectral-line elimination. These phenomena can be observed in experiment since the rigorous condition of near-degenerate levels with nonorthogonal dipole moments is not required here. Qualitatively, these phenomena can be attributed to the quantum interference between competitive spontaneous-decay channels in the bare-state picture or the spontaneously generated coherence between two close-lying levels in the dressed-state picture.

We present a theoretical analysis of trichromatic phase manipulation of electromagnetically induced transparency and show that it is possible to obtain double switching, in which switching from normal to anomalous dispersion occurs in two separate frequency regimes. In particular, a four-level system in the N configuration is considered, in which electromagnetically induced transparency is established in the $\Lambda$ subsystem and the additional transition is connected to the probe transition and is coupled by a trichromatic field. It is shown that the sum of the relative phases of the sideband components compared to that of the central component plays a crucial role in the absorption and dispersion spectra. Normal dispersion with negligible absorption or anomalous dispersion with small gain can be achieved in multiple-frequency regimes by varying the sum of the relative phases. When the sum phase is changed from 0 to $\pi$, switching from normal to anomalous dispersion occurs in the two different frequency regimes. On the other hand, so long as we fix the sum of two relative phases, the absorption and dispersion spectra keep their own features unchanged no matter how we vary the respective relative phases.

We have investigated the radiative decay of the metastable level $5d{}^{4}D_{7∕2}$ in ${\mathrm{Xe}}^{+}$. Theoretically we find the decay to be heavily dominated by an $M2$ transition and not by $M1∕E2$ transitions. Lifetime measurements of $5d{}^{4}D_{7∕2}$ in a storage ring are difficult since magnetic mixing of the metastable with a short-lived level quenches its population. Decay rates were determined at different magnetic field strengths $\left(B\right)$ in order to allow a nonlinear extrapolation to $B=0$. The experimental lifetime of $2.4\pm 0.8\mathrm{s}$ was in agreement with the calculated value, but much smaller than previously estimated.

An elementary formula for the von Neumann and Rényi entropies describing quantum correlations in two-fermionic systems having four single-particle states is presented. An interesting geometric structure of fermionic entanglement is revealed. A connection with the generalized Pauli principle is established.

The propagation of ultracold atomic gases through abruptly changing waveguide potentials is examined in the limit of noninteracting atoms. Time-independent scattering calculations of microstructured waveguides with discontinuous changes in the transverse harmonic binding potentials are used to mimic waveguide perturbations and imperfections. Three basic configurations are examined: steplike, barrierlike, and well-like with waves incident in the ground mode. At low energies, the spectra rapidly depart from single moded, with significant transmission and reflection of excited modes. The high-energy limit sees 100% transmission, with the distribution of the transmitted modes determined simply by the overlap of the mode wave functions and interference.

The dynamical response of a laser simultaneously subject to frequency-shifted optical feedback and pump modulation is investigated both theoretically and experimentally. A theoretical bifurcation analysis shows that the intensity modulation contrast induced by the frequency-shifted optical feedback can be amplified by modulating the laser pump power near a parametric instability. We show that this amplification is phase sensitive and more significant at a weak optical feedback level. Compared with conventional optical heterodyne detection, this method permits higher sensitive interferometry and hence imaging.

The existence and stability of solitons in Bose-Einstein condensates with attractive interatomic interactions, described by the Gross-Pitaevskii equation with a three-dimensional (3D) periodic potential, are investigated in a systematic form. We find a one-parameter family of stable 3D solitons in a certain interval of values of their norm, provided that the strength of the potential exceeds a threshold value. The minimum number of ${}^7\mathrm{Li}$ atoms in the stable solitons is 60, and the energy of the soliton at the stability threshold is $\approx 6$ recoil energies in the lattice. The respective energy versus norm diagram features two cuspidal points, resulting in a typical swallowtail pattern, which is a generic feature of 3D solitons supported by quasi-two-dimensional or fully dimensional lattice potentials.

Two electrons subject to the Coulomb interaction and confined by an anisotropic harmonic potential can be viewed in two ways. One is the “Hooke’s atom,” much used in density functional theory (DFT), but with the addition of an external magnetic field. The other is as a heliumlike three-dimensional quantum dot. Though some results on the systems are known in both the DFT and quantum dot literature, exact analytical solutions have been lacking for nonzero anisotropy (nonzero $B$). For certain specific confinement strengths, we develop such solutions in closed form, hence include electron exchange and correlation exactly. As with the zero-field Hooke’s atom, those solutions can be the ground or excited states.