Systems in the dispersive regime of cavity quantum electrodynamics (QED) are approaching the limits of validity of the dispersive approximation. We present a model which takes into account nonlinear corrections to the dressing of the atom by the field. We find that in the presence of pure dephasing, photons populating the cavity act as a heat bath on the atom, inducing incoherent relaxation and excitation. These effects are shown to reduce the achievable signal-to-noise ratio in cavity QED realizations where the atom is measured indirectly through cavity transmission and in particular in circuit QED.

In this Rapid Communication, we show analytically that all pure entangled states of two $d$-dimensional systems (qudits) violate the Collins-Gisin-Linden-Masser-Popescu (CGLMP) inequality. This property was pointed out by Gisin in the qubit case and then generalized by Gisin-Peres and Popescu-Rohrlich to the qudit case based on the Clauser-Horne-Shimony-Holt (CHSH) inequality. We report the Gisin’s theorem for two qudits by making use of the CGLMP inequality.

We describe a three-dimensional geometry in which both attractive and repulsive Casimir forces arise using ordinary metallic materials, as computed via an exact numerical method (no uncontrolled approximations). The geometry consists of a zipperlike, glide-symmetric structure formed of interleaved metal brackets attached to parallel plates—because of the interleaving pattern, a net repulsive force can arise from a combination of attractive interactions. Depending on the separation, the perpendicular force between the plates and brackets varies from attractive (large separations) to repulsive (intermediate distances) and back to attractive (close separations), with one point of stable equilibrium in the perpendicular direction. This geometry was motivated by a simple intuition of attractive interactions between surfaces, and so we also consider how a rough proximity-force approximation of pairwise attractions compares to the exact calculations.

A quantum key distribution with decoherence-free subspaces has been proposed to overcome collective noise to the polarization modes of photons flying in quantum channels. Prototypes of this scheme have also been achieved with a parametric down-conversion source. However, the photon-number-splitting attack we propose will make practical implementations of this scheme insecure since the parametric down-conversion source may occasionally emit multiphoton pairs. We propose a decoy-state method to make these implementations immune to this attack. With this decoy-state method, both the security distance and key bit rate will be increased.

We propose a simple technique for the generation of arbitrary-sized Dicke states in a chain of trapped ions. The method uses global addressing of the entire chain by two pairs of delayed but partially overlapping laser pulses to engineer a collective adiabatic passage along a multi-ion dark state. Our technique, which is a many-particle generalization of the stimulated Raman adiabatic passage technique, is decoherence free with respect to spontaneous emission and robust against moderate fluctuations in the experimental parameters. Furthermore, because the process is very rapid, the effects of heating are almost negligible under realistic experimental conditions. We predict that the overall fidelity of synthesis of a Dicke state involving ten ions sharing two excitations should approach 98% with currently achievable experimental parameters.

Using the $4s^{\prime }{\left[1/2\right]}_0$ and $4s{\left[3/2\right]}_2$ metastable states of argon created in a plasma discharge we perform photoionization spectroscopy of even-parity autoionizing $\text{Ar}\left(n{p}^{\prime }\right)$ Rydberg states between the first and second ionization limits. Fitting the data to a sum of Fano-type or Shore-type profiles allows us to extract the widths and energies of the three overlapping resonance states ${\left[1/2\right]}_1$, ${\left[3/2\right]}_1$, and ${\left[3/2\right]}_2$ in the $11p^{\prime }$ manifold. We compare the experimental analysis of the $11p^{\prime }$ multiplet to theoretical calculations which are based on the configuration interaction Pauli-Fock approach with core polarization. Agreement between the experimental and theoretical resonance parameters is good.

We experimentally realize an atom cavity consisting of a magnetic trap and an optical lattice that extends over the whole trap. When displaced sufficiently from the center of the magnetic trap, dynamics of the atoms are characterized by magnetic confinement on one side of the cavity and Bragg reflection due to the optical lattice on the other side. We demonstrate this atom cavity by recording the momentum-space oscillation of a Bose-Einstein condensate inside the cavity as a function of time. This atom-cavity configuration presents the possibility of realizing a Mach-Zehnder-type atom interferometer.

Path-entangled $N$-photon systems described by NOON states are the main ingredient of many quantum information and quantum imaging protocols. Our analysis aims to lead the way toward the implementation of both NOON-state sources and their applications. To this end, we study the functionality of “real” NOON-state sources by quantifying the effect real experimental apparatuses have on the actual generation of the desired NOON state. In particular, since the conditional generation of NOON states strongly relies on photon counters, we evaluate the dependence of both the reliability and the signal-to-noise ratio of “real” NOON-state sources on detection losses. We find a surprising result: NOON-state sources relying on nondetection are much more reliable than NOON-state sources relying on single-photon detection. Also the comparison of the resources required to implement these two protocols comes out to be in favor of NOON-state sources based on nondetection. A scheme to improve the performances of “real” NOON-state sources based on single-photon detection is also proposed and analyzed.

We present a nonlocal entanglement concentration scheme for reconstructing some maximally entangled multipartite states from partially entangled ones by exploiting cross-Kerr nonlinearities to distinguish the parity of two polarization photons. Compared with entanglement concentration schemes based on two-particle collective unitary evolution, this scheme does not require the parties to know accurately information about the partially entangled states—i.e., their coefficients. Moreover, it does not require the parties to possess sophisticated single-photon detectors, which makes this protocol feasible with present techniques. By iteration of entanglement concentration processes, this scheme has a higher efficiency and yield than those with linear optical elements. All these advantages make this scheme more efficient and more convenient than others in practical applications.

Electron-impact ionization cross sections for atoms in high-temperature dense plasmas are calculated in a configuration-average distorted-wave method. For those conditions in which the Coulomb coupling parameter is small, we use the Debye-Hückel potential to screen the projectile electron from the nucleus and target electrons. Ionization cross sections are calculated for both ${\text{Ne}}^{4+}$ and ${\text{Au}}^{47+}$ at high temperatures and various electron densities up to $1.0\times {10}^{25}{\text{cm}}^{-3}$. In general we find that as the density increases, the ionization cross section decreases at all incident energies. We also find that as the charge on the atomic ion becomes larger, the relative density effect becomes smaller.

Differential and integral cross sections for electron-impact excitation of the dipole-allowed $B{{}^1\Sigma }_{\mathrm{u}}^{+}$ and $C{{}^1\Pi }_{\mathrm{u}}$ electronic states of molecular hydrogen have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at the electron-impact energies of 40, 100, and 200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to investigate some ambiguities between earlier experimental data and recent BEf-scaled cross sections as defined and calculated by Kim [J. Chem. Phys. 126, 064305 (2007)] and also to extend the energy range of the available data. Optical oscillator strengths, also determined as a part of the present investigation, were found to be in fair accordance with previous measurements and some calculations.

In dielectronic recombination of hydrogenlike ions an intermediate doubly excited heliumlike ion is formed. Since the $K$ shell is empty, both excited electrons can decay sequentially to the ground state. In this paper we analyze the x-ray radiation emitted from doubly and singly excited heliumlike titanium ions produced inside the Tokyo electron beam ion trap. Theoretical population densities of the singly excited states after the first transition and the transition probabilities of these states into the ground state were also calculated. This allowed theoretical branching ratios to be determined for each manifold. These branching ratios are compared to the experimentally obtained x-ray distribution by fitting across the relevant peak using a convolution of the theoretically obtained resonance strengths and energies. By taking into account $2E1$ transitions which are not observed in the experiment, the measured and calculated ratios agree well. This method provides a valuable insight into the transition dynamics of excited highly charged ions.

We study the ionization cross sections of the $K$ shell of Cu and the $L$ shells of Ag, In, and Sn by positron impact using the distorted-wave Born approximation, focusing on the near-threshold energy range (below 40 keV) to compare with recent measurements. The distorted-wave formalism proves to be an appropriate approach, especially to describe the shape of the cross-section curves for positrons accurately. Furthermore, we calculate x-ray production cross sections of the considered $L$ shells having recourse to two sets of atomic relaxation parameters involved in the conversion from ionization to x-ray production cross sections. The 5%–10% differences in the theoretical values calculated with these parameter sets are apparently not large enough to explain the discrepancy between the distorted-wave curves and the experimental data, particularly for Ag. Other sources of uncertainty that could be affecting these comparisons are discussed.

We study superradiant Raman scattering from an ultracold, but finite, temperature Bose gas in a harmonic trap. Numerical simulations indicate the existence of distinct time scales associated with the decoherence of the condensed versus thermal fractions, and the concomitant preferred scattering from atoms in low-lying trap states in the regime where superradiance takes place on a time scale comparable to an inverse trap frequency. As a consequence the scattered atoms experience a modest reduction in temperature as compared to the unscattered atoms.

We investigate the effect of the spontaneous decay-induced coherence on the control of coherent population transfer in a closed double $\Lambda$-type four-level system with the energy separation of the excited doublet comparable to their decay rates by using the stimulated Raman adiabatic passage technique. It is shown that when the two pulse laser fields are tuned to the particular frequency where the condition for quantum interference is satisfied, remarkable enhancement or suppression of population transfer can be realized through the spontaneous emission constructive or destructive quantum interference even with a finite pulse area, which is very favorable to coherent population transfer in quantum systems with weak oscillator strengths.

We present a general scheme to determine the loss-free adiabatic eigensolutions (dark-state polaritons) of the interaction of multiple probe laser beams with a coherently driven atomic ensemble under conditions of electromagnetically induced transparency. To this end we generalize the Morris-Shore transformation to linearized Heisenberg-Langevin equations describing the coupled light-matter system in the weak excitation limit. For the simple lambda-type coupling scheme the generalized Morris-Shore transformation reproduces the dark-state polariton solutions of slow light. Here we treat a closed-loop dual-$V$ scheme wherein two counterpropagating control fields generate a quasistationary pattern of two counterpropagating probe fields—so-called stationary light. We show that contrary to previous predictions, there exists a single unique dark-state polariton; it obeys a simple propagation equation.

We study the properties of solitons in thermal nonlocal media (media having an infinite range of nonlocality) with a periodic refractive index modulation. Such self-localized solutions exist for both signs of the nonlinearity and exhibit a host of features that have no counterpart in local or nonlocal media with finite range nonlocality. Perhaps the most intriguing property is that families of bright solitary pulses can exist inside the bands of the band structure. This property is attributed to the infinite range of nonlocality as well as to the boundary conditions applied to the system. Families of solitons bifurcating from higher-order band edges, otherwise unstable in local media, are found to be stable.

We study an extended velocity-selective coherent population trapping (VSCPT) model where vacuum-induced coherence (VIC) is considered. This effect takes place when two nonorthogonal electric dipole moments of a $\Lambda$-type three-level atom couple with a common continuous vacuum. First, we introduce the main results of a conventional VSCPT model in the nondegenerate and unsymmetrically driven situation. Then, we work out the dynamic equation of the system in the presence of VIC expressed in both internal and external degrees of freedom. We report on the generation of atomic external coherences due to VIC, which counteract the feeding action of spontaneous emission to the trapping state and indicate its limited function negative to the formation of the trapping state if the atomic center-of-mass motion is considered.

A number of approaches to the arrival time problem employ a complex potential of a simple step function type and the arrival time distribution may then be calculated using the stationary scattering wave functions. Here, it is shown that in the Zeno limit (in which the potential becomes very large), the arrival time distribution may be obtained in a clear and simple way using a path integral representation of the propagator together with the path decomposition expansion (in which the propagator is factored across a surface of constant time). Crucially, this method shows that the resulting arrival time distribution, in the Zeno limit, is in fact independent of the form of the complex potential.