In this paper, we propose a kind of illusion cloak that does not provide invisibility but instead changes the scattering of a coated target to that of a totally different one. Different from other illusion cloaks such as those based on “anti-object” or active sources, the proposed one is independent of the information of concealed targets or incident waves and can reshape the scattering of any targets. In addition, we also provide a general method to imitate arbitrary conductor line segments, as a special case of conductor reshaper. Electromagnetic (EM) simulations by a finite-element solver on detailed examples have been carried to validate the design.

We theoretically analyze the second-harmonic generation process in a sequence of unidirectionnaly coupled doubly resonant whispering gallery mode semiconductor resonators. By using a convenient design, it is possible to coherently sum the second-harmonic fields generated inside each resonator. We show that resonator coupling allows the bandwidth of the phase-matching curve to be increased with respect to single-resonator configurations simultaneously taking advantage of the resonant feature of the resonators. This quasi-phase-matching technique could be applied to obtain small-footprint nonlinear devices with large bandwidth and limited nonlinear losses. The results are discussed in the framework of the slow-light-effect enhancement of second-order optical nonlinearities.

For several decades it was believed that information-secure key distribution requires both the sender and receiver to have the ability to generate and/or manipulate quantum states. Earlier, we showed that quantum key distribution in which one party is classical is possible [Boyer, Kenigsberg, and Mor, Phys. Rev. Lett. 99, 140501 (2007)]. A surprising and very nice extension of that result was suggested by Zou, Qiu, Li, Wu, and Li [Phys. Rev. A 79, 052312 (2009)]. Their paper suggests that it is sufficient for the originator of the states (the person holding the quantum technology) to generate just one state. The resulting semiquantum key distribution, which we call here “quantum key distribution with classical Alice” is indeed completely robust against eavesdropping. However, their proof (that no eavesdropper can get information without being possibly detected) is faulty. We provide here a fully detailed and direct proof of their very important result.

In the preceding Comment [Phys. Rev. A 83, 046301 (2011)], Boyer and Mor pointed out that the first conclusion of Lemma 1 in our paper [X. Zou, D. Qiu, L. Li, L. Wu, and L. Li, Phys. Rev. A 79, 052312 (2009)] is not correct, and therefore, the proof of Theorem 5 based on Lemma 1 is wrong. Furthermore, they gave a direct proof for Theorem 5 and affirmed the conclusions in our original paper. In this Reply, we admit the first conclusion of Lemma 1 is not correct, but we need to point out that the second conclusion of Lemma 1 is correct. Accordingly, all the proofs for Lemma 2, Lemma 3, and Theorems 3–6 are based only on the second conclusion of Lemma 1 and therefore are correct.

Observations of the $(3d^{10}4s^2){}^1{S}_0\to (3d^{10}4s5s){}^3{S}_1$ excitation process in zinc, with incident spin-polarized electrons, show significant deviations from expectations for a pure electron exchange transition. This result, derived from values of up to 10% of the Stokes parameter $P_2$ (aligned linear polarization) of the light emitted in the $(3d^{10}4s5s){}^3{S}_1\to (3d^{10}4s4p){}^3{P}_{0,1,2}$ optical decays, is very different from predictions of near-zero values from general theory as well as sophisticated, relativistic close-coupling and distorted-wave numerical models. Although the linear light polarization $P_2$ may be nonzero by parity conservation, it was expected to vanish due to dynamical symmetries.

In a recent paper [M. Huber et al., Phys. Rev. Lett. 104, 210501 (2010)], new criteria to determine the presence of multipartite entanglement were given. We exploit these tools to study thermal entanglement in a spin-star network made of three peripheral spins interacting with a central one. Genuine tripartite entanglement is found in a wide range of the relevant parameters. A comparison between predictions based on the new criteria and those based on the tripartite negativity is also made.

In this paper, we use the concurrence vector as a measure of entanglement, and investigate lower and upper bounds on the concurrence of a superposition of bipartite states as a function of the concurrence of the superposed states. We show that the amount of entanglement quantified by the concurrence vector is exactly the same as that quantified by $I$ concurrence, so that our results can be compared to those given in Phys. Rev. A 76, 042328 (2007). We obtain a tighter lower bound in the case in which the two superposed states are orthogonal. We also show that when the two superposed states are not necessarily orthogonal, both lower and upper bounds are, in general, tighter than the bounds given in terms of the $I$ concurrence. An extension of the results to the case with more than two states in the superpositions is also given.

We suggest and demonstrate an all-optical experimental setup to observe and engineer entanglement oscillations of a pair of polarization qubits in an effective non-Markovian channel. We generate entangled photon pairs by spontaneous parametric down-conversion (SPDC), and then insert a programmable spatial light modulator in order to impose a polarization-dependent phase shift on the spatial domain of the SPDC output. This creates an effective programmable non-Markovian environment where modulation of the environment spectrum is obtained by inserting a spatial grating on the signal arm. In our experiment, programmable oscillations of entanglement are achieved, where the entangled state obtained at the maximum of the revival after sudden death violates Bell’s inequality by $17$ standard deviations.

We present a scheme to realize a special quantum cloning machine in separate cavities. The quantum cloning machine can copy the quantum information from a photon pulse to two distant atoms. Choosing the different parameters, the method can perform optimal symmetric (asymmetric) universal quantum cloning and optimal symmetric (asymmetric) phase-covariant cloning.

We describe in detail how to perform universal fault-tolerant quantum computation on a two-dimensional color code, making use of only nearest neighbor interactions. Three defects (holes) in the code are used to represent logical qubits. Triple-defect logical qubits are deformed into isolated triangular sections of color code to enable transversal implementation of all single logical qubit Clifford group gates. Controlled-NOT (CNOT) is implemented between pairs of triple-defect logical qubits via braiding.

We present results from a joint experimental and theoretical study of elastic electron scattering from atomic iodine. The experimental results were obtained by subtracting known cross sections from the measured data obtained with a pyrolyzed mixed beam containing a variety of atomic and molecular species. The calculations were performed using both a fully relativistic Dirac $B$-spline $R$-matrix (close-coupling) method and an optical model potential approach. Given the difficulty of the problem, the agreement between the two sets of theoretical predictions and the experimental data for the angle-differential and the angle-integrated elastic cross sections at 40 eV and 50 eV is satisfactory.

We have studied magnetic Feshbach resonances in an ultracold sample of Na prepared in the absolute hyperfine ground state. We report on the observation of three $s$-, eight $d$-, and three $g$-wave Feshbach resonances, including a more precise determination of two known $s$-wave resonances, and one $s$-wave resonance at a magnetic field exceeding 200 mT. Using a coupled-channels calculation we have improved the sodium ground-state potentials by taking into account these new experimental data and derived values for the scattering lengths. In addition, a description of the molecular states leading to the Feshbach resonances in terms of the asymptotic-bound-state model is presented.

Low-order relativistic perturbation-theory calculations are carried out for dielectronic recombination cross sections for ${\mathrm{C}}^{3+}$ above and below the ionization threshold. Cross-sectional calculations are made for the 38 levels of the $1s^{2}2p4l$ resonance configurations that lie within $\pm$1.0 eV of the ionization threshold. The below-threshold calculations predict an unobserved strong resonance feature and provide a guide for future experiments.

We present high-resolution photoelectron–Auger-electron coincidence spectra of methane (${\mathrm{CH}}_4$). Since the vibrational structure in the photoelectron spectrum is resolved, the Auger spectra corresponding to different vibrational levels can be separated. The seven final states of ${\mathrm{CH}}_4^{2+}$ are either dissociative or metastable, but in any case are populated in a repulsive part of their potential-energy curve via the Auger decay. The Auger line shapes can therefore be obtained by mapping the vibrational wave functions of the core-hole state into energy space. We have implemented this connection in the data analysis. By simultaneously fitting the different Auger spectra, detailed information on the energies of the dicationic states and their repulsive potential-energy curves is derived.

We consider a theoretical model of a four-mode Bose-Hubbard model consisting of two pairs of wells coupled via two processes with two different rates. The model is naturally divided into two subsystems with strong intrasystem coupling and much weaker coupling between the two subsystems and has previously been introduced as a model for Josephson heat oscillations by Strzys and Anglin [Phys. Rev. A 81, 043616 (2010)]. We examine the quantum dynamics of this model for a range of different initial conditions, in terms of both the number distribution among the wells and the quantum statistics. We find that the time evolution is different to that predicted by a mean-field model and that this system exhibits a wide range of interesting behaviours. We find that the system equilibrates to a maximum entropy state and is thus a useful model for quantum thermalisation. As our model may be realized to a good approximation in the laboratory, it becomes a candidate for experimental investigation.

It has been a longstanding goal in quantum optics to realize controllable sources generating joint multiphoton states, particularly photon triplet with arbitrary spectral characteristics. We demonstrate that such sources can be realized via cascaded parametric down-conversion (PDC) in superlattice structures of nonlinear and linear segments. We consider a scheme that involves two parametric processes—${\omega }_0\to {\omega }_1+{\omega }_2$, ${\omega }_2\to {\omega }_1+{\omega }_1$ under pulsed pump—and investigate the spontaneous creation of a photon triplet as well as the generation of high-intensity mode in intracavity three-photon splitting. We show the preparation of Greenberger-Horne-Zeilinger polarization-entangled states in cascaded type-II and type-I PDC in the framework of considering the dual-grid structure that involves two periodically poled crystals. We demonstrate the method of compensation of the dispersive effects in nonlinear segments by appropriately chosen linear dispersive segments of superlattice for preparation of the heralded joint states of two polarized photons. In the case of intracavity three-photon splitting, we concentrate on the investigation of photon-number distributions, third-order photon-number correlation function, as well as the Wigner functions. These quantities are observed both for short interaction time intervals and the over-transient regime, when dissipative effects are essential.

We present a quantitative x-ray phase imaging method that can be readily implemented on existing x-ray microscopy facilities. This technique utilizes Fresnel zone plates both as imaging optical elements for magnification and as second-order grating structures for phase-shifting interferometry. By making high-resolution quantitative x-ray phase information widely available, we expect this work to have significant impact on nanoscale biological and material studies.

We consider vortex rings moving in a Bose–Einstein condensate. By numerically solving the Gross–Pitaevskii equation, we show that if the circular shape of the ring is perturbed by helical Kelvin waves of given amplitude and azimuthal wave number, the translational self-induced velocity of the vortex ring is reduced; at large amplitude, the vortex ring halts.

We study subadditivity of the minimum output entropy ($H_{\text{min}}$) of quantum multiple access channels (MACs). We provide an example of violation of the additivity theorem for $H_{\text{min}}$ known in classical information theory. Our result is based on a fundamental property of $\text{MACs}$, i.e., independence of each sender. The channels used in the example can be constructed explicitly. On the basis of subadditivity of $H_{\text{min}}$ we also provide an example of extremal superadditivity (superactivation) of the classical capacity region of MACs.

We have calculated atomic helium spontaneous decay rates and absorption oscillator strengths for the spin-forbidden transitions from $3\hspace{0.5em}{}^3{P}_{1,2}$ and $3\hspace{0.5em}{}^1{P}_1$ to all lower ${}^1{S}_0$ and ${}^3{S}_1$ states. In particular we found $A_{10}=44.33(4)\hspace{0.5em}{\mathrm{s}}^{-1}$ for the $E$1 transition $3\hspace{0.5em}{}^3{P}_1$–$1\hspace{0.5em}{}^1{S}_0$ and 0.1147(1) ${\mathrm{s}}^{-1}$ for the $M$2 transition $3\hspace{0.5em}{}^3{P}_2$–$1\hspace{0.5em}{}^1{S}_0$.