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Entanglement and polarization of pure, two-qubit systems are known to be constrained by the relationship C 2 + P 2 = 1. Here, C stands for concurrence, a standard measure of entanglement, and P refers to the degree of polarization of either of the two, single-qubit subsystems. The above constraint may be understood as reflecting that a system cannot be in a pure state, if it is entangled with another one. In order to explore the connection between entanglement and polarization beyond two-qubit systems, we addressed states in which at least one of the parties has dimensionality greater than two. The case of pure, tripartite states offered itself as a timely candidate. We focussed on three qubits and studied the connection between one qubit’s polarization and its entanglement with the other two taken together. We derived new constraints, akin to the above one, and submitted them to experimental tests using single photons entangled in polarization. The latter provided two qubits, each one attached to one photon. The third qubit was chosen to be the path (momentum) of one of the photons. Our experimental results confirmed the validity of the new constraints. Our theoretical results hold also for classical light. Possible experimental tests could be done with so-called structured light beams. [ABSTRACT FROM AUTHOR]

We show a way to pattern the visible electroluminescence of solution-processed mesoporous ZnO layers. Our approach consists in locally changing the nanoscale morphology of the coated ZnO layers by patterning the underlying surface with thin metallic patches. Above the metal, the ZnO film is organized in clusters that enhance its defect-induced electroluminescence. The resulting emission occurs over a large continuum of wavelengths in the visible and near-infrared range. This broad emission continuum is filtered by thin film interferences that develop within the device, making it possible to fabricate LEDs with different colours by adjusting the thickness of their transparent electrode. When the metallic patterns used to change the morphology of the ZnO layer reach sub-micron dimensions, additional plasmonic effects arise, providing extra degrees of freedom to tune the colour and polarization of the emitted photons. [ABSTRACT FROM AUTHOR]

The spin effect of electrons/positrons (e−/e+) and polarization effect of γ photons are investigated in the interaction of two counter-propagating linearly polarized laser pulses of peak intensity 8.9 × 1023 W cm−2 with a thin foil target. The processes of nonlinear Compton scattering and nonlinear Breit–Wheeler pair production based on the spin- and polarization-resolved probabilities are implemented into the particle-in-cell (PIC) algorithm by Monte Carlo methods. It is found from PIC simulations that the average degree of linear polarization of emitted γ photons can exceed 50%. This polarization effect leads to a reduced positron yield by about 10%. At some medium positron energies, the reduction can reach 20%. Furthermore, we also observe that the local spin polarization of e−/e+ leads to a slight decrease of the positron yield about 2% and some anomalous phenomena about the positron spectrum and photon polarization at the high-energy range, due to spin-dependent photon emissions. Our results indicate that spin and polarization effects should be considered in calculating the pair production and laser-plasma interaction with the laser power of 10 PW to 100 PW classes. [ABSTRACT FROM AUTHOR]

In a previous paper we showed how higher-order strong-field-QED processes in long laser pulses can be approximated by multiplying sequences of 'strong-field Mueller matrices'. We obtained expressions that are valid for arbitrary field shape and polarization. In this paper we derive practical approximations of these Mueller matrices in the locally-constant- and the locally-monochromatic-field regimes. The spin and polarization can also change due to loop contributions (the mass operator for electrons and the polarization operator for photons). We derive Mueller matrices for these as well, for arbitrary laser polarization and arbitrarily polarized initial and final particles. [ABSTRACT FROM AUTHOR]

Relativistic magnetic reconnection is a potential particle acceleration mechanism for high-frequency BL Lac objects (HBLs). The Imaging X-ray Polarimetry Explorer (IXPE) scheduled to launch in 2021 has the capability to probe the evolution of magnetic field in HBLs, examining the magnetic reconnection scenario for the HBL flares. In this paper, we make the first attempt to self-consistently predict HBL X-ray polarization signatures arising from relativistic magnetic reconnection via combined particle-in-cell and polarized radiation transfer simulations. We find that although the intrinsic optical and X-ray polarization degrees are similar on average, the X-ray polarization is much more variable in both the polarization degree and angle (PD and PA). Given the sensitivity of the IXPE, it may obtain one to a few polarization data points for one flaring event of nearby bright HBLs Mrk 421 and 501. However, it may not fully resolve the highly variable X-ray polarization. Due to temporal depolarization, where the integration of photons with variable polarization states over a finite period of time can lower the detected PD, the measured X-ray PD can be considerably lower than the optical counterpart or even undetectable. The lower X-ray PD than the optical thus can be a characteristic signature of relativistic magnetic reconnection. For very bright flares where the X-ray polarization is well resolved, relativistic magnetic reconnection predicts smooth X-ray PA swings, which originate from large plasmoid mergers in the reconnection region. [ABSTRACT FROM AUTHOR]

By taking the spin and polarization of the electrons, positrons and photons into account in the strong-field QED processes of nonlinear Compton emission and pair production, we find that the growth rate of QED cascades in ultra-intense laser fields can be substantially reduced. While this means that fewer particles are produced, we also found them to be highly polarized. We further find that the high-energy tail of the particle spectra is polarized opposite to that expected from Sokolov–Ternov theory, which cannot be explained by just taking into account spin-asymmetries in the pair production process, but results significantly from 'spin-straggling'. We employ a kinetic equation approach for the electron, positron and photon distributions, each of them spin/polarization-resolved, with the QED effects of photon emission and pair production modelled by a spin/polarization dependent Boltzmann-type collision operator. For photon-seeded cascades, depending on the photon polarization, we find an excess or a shortage of particle production in the early stages of cascade development, which provides a path towards a controlled experiment. Throughout this paper we focus on rotating electric field configuration, which represent an idealized model and allows for a straightforward interpretation of the observed effects. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate that tomographic measurements can be performed for states of qubits before they are prepared. A variant of the quantum teleportation protocol is used as a channel between two instants in time, allowing measurements for polarization states of photons to be implemented 88 ns before they are created. Measurement data taken at the early time and later unscrambled according to the results of the protocol's Bell measurements, produces density matrices with an average fidelity of 0.90±0.01 against the ideal states of photons created at the later time. Process tomography of the time reverse quantum channel finds an average process fidelity of 0.84±0.02. While our proof-of-principle implementation necessitates some post-selection, the general protocol is deterministic and requires no post-selection to sift desired states and reject a larger ensemble. [ABSTRACT FROM AUTHOR]

We propose and evaluate the performance of an improved preclinical positron emission tomography (PET) scanner design, referred to as Polaroid-PET, consisting of a detector equipped with a layer of horizontal Polaroid to filter scintillation photons with vertical polarization. This makes it possible to improve the spatial resolution of PET scanners based on monolithic crystals. First, a detector module based on a lutetium-yttrium orthosilicate monolithic crystal with 10 mm thickness and silicon photomultipliers (SiPMs) was implemented in the GEANT4 Monte Carlo toolkit. Subsequently, a layer of Polaroid was inserted between the crystal and the SiPMs. Two preclinical PET scanners based on ten detector modules with and without Polaroid were simulated. The performance of the proposed detector modules and corresponding PET scanner for the two configurations (with and without Polaroid) was assessed using standard performance parameters, including spatial resolution, sensitivity, optical photon ratio detected for positioning, and image quality. The detector module fitted with Polaroid led to higher spatial resolution (1.05 mm FWHM) in comparison with a detector without Polaroid (1.30 mm FHWM) for a point source located at the center of the detector module. From 100% of optical photons produced in the scintillator crystal, 65% and 66% were used for positioning in the detectors without and with Polaroid, respectively. Polaroid-PET resulted in higher axial spatial resolution (0.83 mm FWHM) compared to the scanner without Polaroid (1.01 mm FWHM) for a point source at the center of the field of view (CFOV). The absolute sensitivity at the CFOV was 4.37% and 4.31% for regular and Polaroid-PET, respectively. Planar images of a grid phantom demonstrated the potential of the detector with a Polaroid in distinguishing point sources located at close distances. Our results indicated that Polaroid-PET may improve spatial resolution by filtering the reflected optical photons according to their polarization state, while retaining the high sensitivity expected with monolithic crystal detector blocks. [ABSTRACT FROM AUTHOR]

The angular distribution of O 1s photoelectrons emitted from uniaxially oriented methanol is studied experimentally and theoretically. We employed circularly polarized photons of an energy of hν = 550 eV for our investigations. We measured the three-dimensional photoelectron angular distributions of methanol, with the CH3–OH axis oriented in the polarization plane, by means of cold target recoil ion momentum spectroscopy. The experimental results are interpreted by single active electron calculations performed with the single center method. A comparative theoretical study of the respective molecular-frame angular distributions of O 1s photoelectrons of CO, performed for the same photoelectron kinetic energy and for a set of different internuclear distances, allows for disentangling the role of internuclear distance and the hydrogen atoms of methanol as compared to carbon monoxide. [ABSTRACT FROM AUTHOR]

Chiroptical and optical activity effects involve differential interactions between matter and light. Generally this involves chiral molecules absorbing or scattering right- and left-handed circularly polarized photons at different rates due to the chiroptical interplay of molecular and optical chirality. Laser light which propagates with a helical phase and twisted wavefront possesses optical orbital angular momentum. These optical vortices can twist either clockwise or anticlockwise, and as such they exhibit an optical handedness or chirality completely distinct from that of circular polarization. It has recently been established that the linear optical effects of single-photon absorption and scattering can exhibit optical activity and chiroptical interactions with respect to the optical vortex handedness. Here a fundamental mechanism of optical activity for twisted light is exhibited in nonlinear processes, with specific emphasis on hyper-Rayleigh and hyper-Raman scattering. In comparison to unstructured or plane-wave light, it is shown that using twisted photons produces novel scattering mechanisms dependent on parameters unique to optical vortex beams. Specifically, the scattered intensity for both hyper-Rayleigh and hyper-Raman optical activity is dependent on the sign and magnitude of the OAM of the incident twisted photons, as well as the transverse position of the chiral scatterer. Moreover, symmetry analysis reveals that, unlike the recently discovered linear optical activity effects with optical vortices, nonlinear scattering of twisted light by chiral molecules leads to a modification of scattering through uniquely weighted individual hyperpolarizability contributions. [ABSTRACT FROM AUTHOR]

We demonstrate that the present superaccurate measurements of transition processes between atomic states in a hydrogen atom reached the limit of accuracy when transition the frequency could not be defined anymore in a unique way. This was predicted earlier and is due to the necessity to include the nonresonant corrections in the description of resonant processes. The observed spectral line profile becomes asymmetric, and it becomes impossible to extract the value of transition frequency from this profile in a unique way. Nonresonant corrections depend on the type of experiment and on the experimental arrangement. However, the line profile itself for any resonant process can be defined with any desired level of accuracy. A popular trend in the modern search for atomic frequency standards and atomic clocks is the search for transitions where the nonresonant corrections are negligible. In this paper we present closed expressions for the resonant photon scattering cross sections on an atomic level with dependence on all atomic quantum numbers including fine and hyperfine structures. These expressions are given for different types of experiments with fixing of the incident (outgoing) photon propagation directions and incident (outgoing) photon polarization. Using these expressions we demonstrate that the transition frequencies in particular cases cannot be derived uniquely if the accuracy of measurement reaches the level quoted in Beyer et al (2017 Science 358 79). The definition of transition frequency suggested in Beyer et al may become unique with additional requirements to the process of measurement: the use of the 'magic angle' in an experimental arrangement and summation over all possible final states including the hyperfine sublevels. Our interpretation of the results of this experiment is alternative to the interpretation given by Beyer et al. [ABSTRACT FROM AUTHOR]

A model for the reaction is presented with the t-channel π + ρ exchanges reggeized to describe the reaction up to high energies. Gauge invariance of ρ exchange is discussed in connection with the convergence of the reaction cross section at high energies. The roles of electromagnetic (EM) multipole moments of Δ++ baryon and ρ−meson are analyzed in total and differential cross sections and spin density matrix elements. Photon polarization asymmetry Σ is predicted for the measurement of electromagnetic moments of ρ−and Δ++. [ABSTRACT FROM AUTHOR]

The polarization properties of γ-rays elastically scattered by atoms have become more observable with the development of polarized photon beams. However, systematic studies are required to explore the elastic scattering in the MeV-energy range of the spectrum where Delbrück scattering becomes more significant, especially at large scattering angles. We implement a new Monte Carlo simulation to account for the polarization effects of elastic scattering. The simulation is based on explicit expressions driven in the formalism of Stokes parameters. The scattering amplitudes of Rayleigh, nuclear Thomson, and Delbrück scattering processes are superimposed onto a two orthogonal set of complex amplitudes. This set is then exploited to construct the core of the simulation in such a way that the simulation can handle arbitrary polarization states of the incoming beam and correspondingly generate polarization states of the outgoing beam. We demonstrate how the polarization of scattered photons is affected by the polarization of incoming photons. In addition, we explain the dependence of depolarization on the azimuthal angle. [ABSTRACT FROM AUTHOR]

Synchrotron radiation and Compton scattering are widely accepted as the most likely emission mechanisms of some astrophysical phenomena, such as gamma-ray bursts (GRBs) and active galactic nuclei. The measurement of the polarization of photons provides a useful tool to distinguish different emission mechanisms and structures of the emission region. Based on the differential cross section of a polarized photon scattered by an unpolarized electron of any initial momentum, we derive an analytical formula of polarization for beamed photons scattered by isotropic electrons with a power-law distribution. Numerical calculations are carried out in four special cases: electrons at rest, Thomson limit, head-on collision, and monochromatic electrons. It is found that the maximum polarization can be as high as 100% for low energy photons, if the electrons are at rest. Although polarization is highly suppressed due to the isotropic electrons, a maximum value of ∼10%-20% can still be achieved. The Compton scattering process can be used to explain the polarization of GRB 041219A and GRB 100826A. [ABSTRACT FROM AUTHOR]

The article discusses the curvature radiation produced in pulsar magnetosphere and the analytical calculation of the repeated scatterings of unpolarized photons. Topics include the features of polarization for the curvature radiation, the dependence of cone-dominant pulsar with frequency, and the use of nonrelativistic electrons to determine the repeated scatterings of unpolarized photons in a static and uniform magnetic field.

In this paper we present a quantum Cheshire Cat. In a pre- and post-selected experiment we find the Cat in one place, and its grin in another. The Cat is a photon, while the grin is its circular polarization. [ABSTRACT FROM AUTHOR]

We investigate the angular distribution of electrons that are emitted in the ionization of hydrogen-like ions by twisted photons. Analysis is performed based on the first-order perturbation theory and the non-relativistic Schrödinger equation. Special attention is paid to the dependence of the electron emission pattern on the impact parameter b of the ion with respect to the centre of the twisted wave front. In order to explore such a dependence, detailed calculations were carried out for the photoionization of the 1s ground and 2 py excited states of neutral hydrogen atoms. Based on these calculations, we argue that for relatively small impact parameters, the electron angular distributions may be strongly affected by altering the position of the atom within the wave front. In contrast, if the atom is placed far from the front centre, the emission pattern of the electrons is independent of the impact parameter b and resembles that observed in the photoionization by plane wave photons. [ABSTRACT FROM AUTHOR]

We report a controllable method for producing mixed two-photon states via spontaneous parametric down-conversion with a two-type-I crystal geometry. By using variable polarization rotators (VPRs), one obtains mixed states of various purities and degrees of entanglement depending on the parameters of the VPRs. The generated states are characterized by quantum state tomography. The experimental results are found to be in good agreement with the theory. The method can be easily implemented for various experiments that require the generation of states with controllable degrees of entanglement or mixedness. [ABSTRACT FROM AUTHOR]

This paper reports that selective removal of a CuIn1-xGaxSe2 (CIGS) thin film on a Mo-coated glass substrate can be achieved with no edge melting or damage of the Mo layer using a nanosecond Nd :YAG laser with a wavelength of 1064 nm. It is shown that the two crucial parameters that determine the possibility of clean removal of only the CIGS layer are Ga concentration of the CIGS film and laser fluence. For CIGS films with Ga/(Ga+In) ratio greater than about 0.2 for which the band gap energy is close to or over the photon energy (1.17 eV), laser-induced thermal expansion proved to be the mechanism of film removal that drives an initial bulging of the film and then fracture into tens of micrometre sized fragments as observed in in situ shadowgraph images. The fracture-type removal of CIGS films was further verified by scanning electron micrographs of the craters showing that the original shapes of the CIGS polycrystals remain intact along the crater rim. A numerical simulation of film temperature under the irradiation conditions of selective removal was carried out to show that the magnitude of induced thermal stress within the film closely agreed to the yield strength of the CIGS thin film. The results confirmed that a nanosecond laser could be a better choice for P2 and P3 scribing of CIGS thin films if process conditions are properly determined. [ABSTRACT FROM AUTHOR]

In this paper, the UV spectrum of the OH radical (transition A 2Σ → X 2Π) is used to find easy and reliable methods to measure both rotational and vibrational temperatures. A numerical simulation is developed to compute synthetic OH spectra between 300 and 330 nm with a normalization on a lines group called Gref , located at 309 nm. A large number of spectra are computed with different temperatures and global apparatus functions, a quantity which contains all the line broadening sources. Their study allows us to show that amplitude of some 0-0 band's line groups and global apparatus functions or Gref widths are usable to carry out the rotational temperature. Moreover, it is proved that vibrational temperature is accessible through the mean spectrum value of a part of the 1-1 band. To overcome the difficulty of finding the part where the spectrum mean value is evaluated, the authors propose to work with multiples of 'on spectrum accessible lengths'. Abacuses are presented to connect each quantity of interest to temperatures. Finally, proposed methods are checked first experimentally on an oxy-acetylene torch and then on spectra produced with the LIFBASE software. [ABSTRACT FROM AUTHOR]

We present an efficient entanglement concentration protocol (ECP) for the less-entangledWstate with some identical conventional polarized single photons. In the protocol, two of the parties say Alice and Charlie should perform the parity check measurements and they can ultimately obtain the maximally entangled W state with a certain success probability. Otherwise, they can obtain another less-entangled W state, which can be reconcentrated into the maximally entangled W state. By iterating this ECP, a high success probability can be achieved. This ECP may be an optimal one and it is useful in current quantum information processing. [ABSTRACT FROM AUTHOR]

Quantum mechanics violates Leggett-Garg inequalities because the operator formalism predicts correlations between different spin components that would correspond to negative joint probabilities for the outcomes of joint measurements. However, the uncertainty principle ensures that such joint measurements cannot be implemented without errors. In a sequential measurement of the spin components, the resolution and back-action errors of the intermediate measurement can be described by random spin flips acting on an intrinsic joint probability. If the error rates are known, the intrinsic joint probability can be reconstructed from the noisy statistics of the actual measurement outcomes. In this paper, we use the spin-flip model of measurement errors to analyze experimental data on photon polarization obtained with an interferometric setup that allows us to vary the measurement strength and hence the balance between resolution and back-action errors. We confirm that the intrinsic joint probability obtained from the experimental data is independent of measurement strength, and show that the same violation of the Leggett-Garg inequality can be obtained for any combination of measurement resolution and back-action. [ABSTRACT FROM AUTHOR]

Recent experiments have demonstrated an open system realization of the Dicke quantum phase transition in the motional degrees of freedom of an optically driven Bose-Einstein condensate in a cavity. Relevant collective excitations of this light-matter system are polaritonic in nature, allowing access to the quantum critical behavior of the Dicke model through light leaking out of the cavity. This opens the path to using photodetection-based quantum optical techniques to study the dynamics and excitations of this elementary quantum critical system. We first discuss the photon flux observed at the cavity face and find that it displays a different scaling law near criticality than that obtained from the mean-field theory for the equivalent closed system. Next, we study the second-order correlation measurements of photons leaking out of the cavity. Finally, we discuss a modulation technique that directly captures the softening of polaritonic excitations. Our analysis takes into account the effect of the finite size of the system, which may result in an effective symmetry-breaking term. [ABSTRACT FROM AUTHOR]

Tests of the predictions of quantum mechanics for entangled systems have provided increasing evidence against local realistic theories. However, there remains the crucial challenge of simultaneously closing all major loopholes-the locality, freedom-of-choice and detection loopholes-in a single experiment. An important sub-class of local realistic theories can be tested with the concept of 'steering'. The term 'steering' was introduced by Schrödinger in 1935 for the fact that entanglement would seem to allow an experimenter to remotely steer the state of a distant system as in the Einstein-Podolsky-Rosen (EPR) argument. Einstein called this 'spooky action at a distance'. EPR-steering has recently been rigorously formulated as a quantum information task opening it up to new experimental tests. Here, we present the first loophole-free demonstration of EPR-steering by violating three-setting quadratic steering inequality, tested with polarization-entangled photons shared between two distant laboratories. Our experiment demonstrates this effect while simultaneously closing all loopholes: both the locality loophole and a specific form of the freedom-ofchoice loophole are closed by having a large separation of the parties and using fast quantum random number generators, and the fair-sampling loophole is closed by having high overall detection efficiency. Thereby, we exclude-for the first time loophole-free-an important class of local realistic theories considered by EPR. Besides its foundational importance, loophole-free steering also allows the distribution of quantum entanglement secure event in the presence of an untrusted party. [ABSTRACT FROM AUTHOR]

We investigate theoretically two photon entanglement processes in a photonic-crystal cavity embedding a quantum dot in the strong-coupling regime. The model proposed by Johne et al. (Johne R, Gippius N A, Pavlovic G, Solnyshkov D D, Shelykh I A and Malpuech G 2008 Phys. Rev. Lett. 100 240404), and by Robert et al. (Robert J, Gippius N A and Malpuech G 2009 Phys. Rev. B 79 155317) is modified by considering irreversible dissipation and incoherent continuous pumping for the quantum dot, which is necessary to connect the realistic experiment. The dynamics of the system is analysed by employing the Born-Markov master equation, through which the spectra for the system are computed as a function of various parameters. By means of this analysis the photon-reabsorption process in the strongcoupling regime is first observed and analysed from the perspective of radiation spectrum and the optimal parameters for observing energy-entangled photon pairs are identified. [ABSTRACT FROM AUTHOR]

In ion trap quantum information processing, efficient fluorescence collection is critical for fast, high-fidelity qubit detection and ion-photon entanglement. The expected size of future many-ion processors requires scalable light collection systems. We report on the development and testing of a microfabricated surface-electrode ion trap with an integrated high-numerical aperture (NA) micromirror for fluorescence collection. When coupled to a low- NA lens, the optical system is inherently scalable to large arrays of mirrors in a single device. We demonstrate the stable trapping and transport of 40Ca+ ions over a 0.63 NA micromirror and observe a factor of 1.9 enhancement of photon collection compared to the planar region of the trap. [ABSTRACT FROM AUTHOR]

Directionality inherent in the polarization of light affords the means of performing robust dynamic orientational measurements of molecules and asymmetric scatterers. In this paper, the precision with which measurements of this kind can be made is quantified for a number of common polarizationbased measurement architectures using a metric derived from Fisher information. Specifically, a fundamental limit of 0.5 radian per detected photon (on average) is found, thus highlighting the importance of maximizing photon numbers by correct fluorophore selection. Informational dips, whereby measurement precision is degraded, are shown to arise in many realistic measurement scenarios, particularly for inference from null readings. The severity of these precision losses is therefore considered, and it is shown to decrease with increased system redundancy. Contamination of measured data from coherently and incoherently radiating extraneous sources, furthermore, causes a loss of precision. Analytic and numerical results are hence also presented in this vein. [ABSTRACT FROM AUTHOR]

Possible error sources in an experimentally realized linear-optics controlled-Z gate (Okamoto et al 2005 Phys. Rev. Lett. 95 210506) are analyzed by considering the deviations of the beam splitting ratios from the ideal values (δRH, δRV), the polarization-dependent phase shift (birefringence) of the optical components (δϕ) and the mode mismatch of input photons (δξ). It is found that the error rate is linearly dependent on δRV and δξ , while the dependence on δRH and δϕ is approximately quadratic. As a practical result, the gate is much more sensitive to small errors in RV than in RH. Specifically, the reflectivity error for vertical polarization must be less than 0.1% to realize a gate with an error of less than 0.1%, whereas the reflectivity error for horizontal polarization can be up to 1%. It is also shown that the effects of different error sources are not independent of each other (linear error model). Under certain conditions, the deviation from the linear error model exceeds 10% of the total error. The method of analysis used illustrates the basic features of errors in general linear optics quantum gates and circuits, and can easily be adapted to any other device of this type. [ABSTRACT FROM AUTHOR]

We investigate the angular and spatial distributions of protons with an energy of 0.223MeV after channeling them through an (11, 9) single-wall carbon nanotube of 0.2μm length. The proton incident angle is varied between 0 and 10 mrad, being close to the critical angle for channeling. We show that, as the proton incident angle increases and approaches the critical angle for channeling, a ring-like structure is developed in the angular distribution--the donut effect. We demonstrate that it is the rainbow effect. If the proton incident angle is between zero and half of the critical angle for channeling, the image force affects considerably the number and positions of the maxima of the angular and spatial distributions. However, if the proton incident angle is close to the critical angle for channeling, its influence on the angular and spatial distributions is considerably decreased.We demonstrate that an increase of the proton incident angle can lead to a significant rearrangement of the propagating protons within the nanotube. This effect may be used to locate atomic impurities in nanotubes as well as for creating nanosized proton beams to be used in materials science, biology and medicine. [ABSTRACT FROM AUTHOR]

The generation of high harmonics from solid-density plasmas promises the production of attosecond (as) pulses orders of magnitude brighter than those from conventional rare gas sources. However, while spatial and spectral emission of surface harmonics has been characterized in detail in many experiments proof that the harmonic emission is indeed phase locked and thus bunched in as-pulses has only been delivered recently (Nomura et al 2009 Nat. Phys. 5 124-8). In this paper, we discuss the experimental setup of our extreme ultraviolet (XUV) autocorrelation (AC) device in detail and show the first twophoton ionization and subsequent AC experiment using solid target harmonics. In addition, we describe a simple analytical model to estimate the chirp between the individual generated harmonics in the sub- and mildly relativistic regime and validate it using particle-in-cell (PIC) simulations. Finally, we propose several methods applicable to surface harmonics to extend the temporal pulse characterization to higher photon energies and for the reconstruction of the spectral phase between the individual harmonics. The experiments described in this paper prove unambiguously that harmonic emission from solid-density plasmas indeed occurs as a train of sub-femtosecond pulses and thus fulfills the most important property for a next-generation as-pulse source of unprecedented brightness. [ABSTRACT FROM AUTHOR]

We propose a protocol to directly implement the nonlocal phase gate of N A-type three-level atoms trapped in distant cavities by using interference of polarized photons. The protocol uses the effects of quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities. [ABSTRACT FROM AUTHOR]

Single-negative materials based on photonic crystal with multiple defect layers are designed and the free modulation of defect modes is studied. The results show that the multi-defect structure can avoid the interference between the defect states. Therefore, the designed double defect modes in the zero effective-phase gap can be adjusted independently by changing the thickness of different defect layers. In addition, the two tunable defect modes have the omnidirectional characteristics. This multi-defect structure with above-mentioned two advantages has potential applications in modern optical devices such as tunable omnidirectional filters. [ABSTRACT FROM AUTHOR]

We propose an experimental scheme to realize the four-dimensional projective measurements for a single photon. The photon polarization and time--energy provide the four-dimensional Hilbert space. Based on this scheme, we suggest an experiment to test the violation of Bell inequalities of four-dimensional systems. In addition, by virtue of a maximally entangled biphoton state, we also show that it is possible to construct a quantum key distribution channel that can provide two-bit key with one pair of entangled photons. [ABSTRACT FROM AUTHOR]

We propose a new linear optical protocol for remote state preparation (RSP) between two parties under control of a number of controllers in terms of optical elements. The realization of this protocol is appealing due to the fact that the quantum state of light is robust against the decoherence, and photons are ideal carriers for transmitting quantum information over long distances. [ABSTRACT FROM AUTHOR]

The radiative biexciton-exciton decay in a semiconductor quantum dot (QD) has the potential of being a source of triggered polarization-entangled photon pairs. However, in most cases the anisotropy-induced exciton fine structure splitting destroys this entanglement. Here, we present measurements on improved QD structures, providing both significantly reduced inhomogeneous emission linewidths and near-zero fine structure splittings. A high-resolution detection technique is introduced which allows us to accurately determine the fine structure in the photoluminescence emission and therefore select appropriate QDs for quantum state tomography. We were able to verify the conditions of entangled or classically correlated photon pairs in full consistence with observed fine structure properties. Furthermore, we demonstrate reliable polarization-entanglement for elevated temperatures up to 30 K. The fidelity of the maximally entangled state decreases only a little from 72% at 4K to 68% at 30 K. This is especially encouraging for future implementations in practical devices. [ABSTRACT FROM AUTHOR]

States can be mapped between the Poincaré space (representing photon polarizations) and the Bloch space (representing states of a quantum spin- ½ particle). Using this mapping and analogous mappings for unitary operators, techniques and formalisms developed in one space can be applied in the other. As an example, error-correction strategies originally developed in the context of pulsed nuclear magnetic resonance experiments are applied to linear optics to propose the design of a new class of composite high-fidelity broadband linear retarder. [ABSTRACT FROM AUTHOR]

We report multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until ∼7000 s postburst. The light curves reveal a chromatic break at ∼400–500 s, with initial temporal decay α = 1.669 ± 0.013 flattening to α ∼ 1 postbreak, which we model as a combination of reverse and forward shock components with magnetization parameter RB ∼ 70. The observed polarization degree decreases from 7.7% ± 1.1% to 2%–4% 52–109 s postburst and remains steady at this level for the subsequent ∼2000 s at a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms that GRB 190114C is highly obscured (Av,HG = 1.49 ± 0.12 mag; cm−2). We interpret the measured afterglow polarization as intrinsically low and dominated by dust —in contrast to the P > 10% measured previously for other GRB reverse shocks—with a small contribution from polarized prompt photons in the first minute. We test whether first- and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and subteraelectronvolt emission but conclude that neither is explained in the reverse shock inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission. [ABSTRACT FROM AUTHOR]

Over the past few decades, impressive progress has been made in the field of photon polarimetry, especially in the hard X-ray and soft gamma-ray energy regime. Measurements of the linear degree of polarization for some of the most energetic astrophysical sources, such as gamma-ray bursts (GRBs) or blazars, are now possible, at energies below the pair creation threshold. As such, a new window has been opened for understanding the exact nature of the nonthermal emission mechanisms responsible for some of the most energetic phenomena in the universe. There are still many open questions and active debates, such as the discrimination between leptonic versus hadronic models of emission for Blazars or ordered versus random field models for GRBs. Because the competing models predict different levels of linear photon polarization at energies above ∼1 MeV, gamma-ray polarimetry in that energy band could provide additional crucial insights. However, no polarimeter for gamma rays with energies above ∼1 MeV has been flown into space, as the sensitivity is severely limited by a quick degradation of the angular resolution and by multiple Coulomb scatterings in the detector. Over the past few years, a series of proposals and demonstrator instruments that aim to overcome those inherent difficulties have been put forth, and the prospects look promising. The paper is organized as follows: Section 1, briefly reviews the history and principles of gamma-ray polarimetry, emphasizing its challenges and successes; Section 2 is dedicated the discussion of gamma-ray polarization and polarimetry, and Section 3 discusses the past and current instruments with which measurements of linear polarization for hard X-rays and soft gamma rays were successfully obtained for astrophysical sources; Section 4 outlines the scientific questions that could be solved by using gamma-ray polarimetry measurements. A summary and outlook are provided in Section 5. [ABSTRACT FROM AUTHOR]

The possibility to use a Hong–Ou–Mandel (HOM) interferometer to carry out gravitational waves detection and spectrometry is investigated. The noise budget of the instrument is evaluated. The basic experimental requirements are calculated. It is shown that the power and wavelength of the heralded photon source, together with the angular accuracy of the measurement of the photon polarization rotation, form the main constraints to determine the type of gravitational waves sources, which would be the target of HOM gravitational wave spectrometers. The currently available pW power heralded photon sources, with typical heralded photon frequencies in the order of 1014 Hz (visible—UV part of the optical spectrum) are totally unsuitable, in terms of required detection time for any of the GW sources, which are presently targeted by ground and space based GW detectors. The operation of the HOM interferometer as a GW spectrometer is illustrated with a numerical model that uses the gravitational wave strain data recorded by LIGO on 14 September 2015 (GW150914 event). Assuming an angular accuracy of rad for the measurement of photons polarization rotation, these measurements could only be carried out with HOM interferometer’s arm lengths of the order of 10.000 km (only achievable in space, if we do not use optical cavities), and by using heralded photon sources of about 1 W power, producing heralded photons with wavelengths in the radio-wave band of the electromagnetic spectrum, 10 MHz. Although the technology to produce this type of heralded photon sources is currently not available, a brief discussion of the possible implementation of a large arm HOM interferometer in space is introduced. [ABSTRACT FROM AUTHOR]

The capability of curved hyperbolic metamaterials to guide the emission of a dipole-emitter into two separate channels depending on the emission helicity with high confinement provides new possibilities for polarization detection. In this work, we numerically demonstrate a novel design of miniature Stokes polarimeter using hyperbolic metamaterial structure coupled with two dipole-emitters. Through determining the four intensity signals arising from the two directional radiation channels of each dipole-emitter, the state of polarization of the incident photons can be analyzed. Numerical simulations also demonstrated that such a design is capable of working with a bandwidth of at least 40 nm. Such a compact full Stokes parameter polarimeter could be a potential candidate for high spatial resolution polarization sensor and imager for a wide variety of applications. [ABSTRACT FROM AUTHOR]

The numerical computation of reliable and accurate Stokes profiles is of great relevance in solar physics. In the synthesis process, many actors play a relevant role: among them the formal solver, the discrete atmospheric model, and the spectral line. This paper tests the performances of different numerical schemes in the synthesis of polarized spectra for different spectral lines and atmospheric models. The hierarchy between formal solvers is enforced, stressing the peculiarities of high-order and low-order formal solvers. The density of grid points necessary for reaching a given accuracy requirement is quantitatively described for specific situations. [ABSTRACT FROM AUTHOR]

In this paper, several novel spin-selected metalenses composed of rotary silicon nanobrick array have been designed and numerically investigated at the telecommunication wavelength of 1500 nm, which can be focused at different positions along transverse or longitudinal direction for different spin light. They can not only directly distinguish the spin states but also manipulate photons with different spin states. Our optimized silicon nanobricks with varying orientation angles can achieve 98% cross-polarized transmitted efficiency, and possess Pancharatnam–Berry phase. Furthermore, a spin-independent metalens has also been designed, which can be well focused at the same spot for the light with different spin states. Our work opens up new avenues toward establishing novel spin-related metadevices, and it is significant for the development of functionality switchable optical devices and spin photonics. [ABSTRACT FROM AUTHOR]

An experiment for the advanced undergraduate laboratory which allows students to study the effect of photon polarisation in Compton scattering and to explore quantum entanglement is described. The quantum entangled photons are produced through electron–positron annihilation in the S-state, and their polarisations are analysed using the Compton scattering cross-section dependence on the photon polarisation. The experiment was equipped with off-the-shelf detectors and electronic units. Finite geometry effects are discussed and investigated with the use of a Geant4-based simulation. [ABSTRACT FROM AUTHOR]

In this paper, we study the effect of the drain current on terahertz detection for Si metal-oxide semiconductor field-effect transistors (MOSFETs) both theoretically and experimentally. The analytical model, which is based on the small-signal equivalent circuit of MOSFETs, predicts the significant improvement of the voltage responsivity Rv with the bias current. The experiment on antennas integrated with MOSFETs agrees with the analytical model, but the Rv improvement is accompanied first by a decrease, then an increase of the low-noise equivalent power (NEP) with the applied current. We determine the tradeoff between the low-NEP and high-Rv for the current-biased detectors. As the best-case scenario, we obtained an improvement of about six times in Rv without the cost of a higher NEP. We conclude that the current supply scheme can provide high-quality signal amplification in practical CMOS terahertz detection. [ABSTRACT FROM AUTHOR]

Single, double, and triple photoionization of Ne+ ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon–ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K- and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne+() level, for example, requires cooperative interaction of at least four electrons. [ABSTRACT FROM AUTHOR]

The optimal design of double quantum well structures for generation of polarization-entangled photons in the mid-infrared range, based on the valence intersubband transitions spontaneous parametric downconversion, is considered. The efficiency and frequency selectivity of the process are also estimated. [ABSTRACT FROM AUTHOR]

State conversion between the Greenberger–Horne–Zeilinger (GHZ) state and the W state is a challenging open problem because these states cannot be converted to each other by just local operations and classical communication. Here we propose a cavity quantum electrodynamics method based on interference of polarized photons emitted by the atoms trapped in spatially separated optical cavities that can convert a three-atom W state to a GHZ state. We calculate the success probability and fidelity of the converted GHZ state when the cavity decay, spontaneous atomic decay and photon leakage of the cavities are taken into account for a practical system, which shows that the proposed scheme is feasible and within the reach of current experimental technology. [ABSTRACT FROM AUTHOR]

The properties of the guided modes, including the single-mode conditions and the coupling of different polarized modes in the single-crystal lithium niobate photonic wires, were analyzed in detail. One-dimensional photonic crystal micro-cavities with several different patterns, which could be used as an ultra-compact optical filter, were designed and simulated in order to get high transmission at the resonant wavelength and the best preferment. The designed structure, with the whole size of 6.5 × 0.7 μm2, was fabricated on a single-mode photonic wire. A measured peak transmission of 0.34 at 1400 nm, an extinction ratio of 12.5 dB and a Q factor of 156 were obtained. The measured transmission spectrum was basically consistent with the simulation, although a slight shift of resonant wavelength occurred due to the fabrication errors. [ABSTRACT FROM AUTHOR]