Linear Optical Method Research Articles

Entanglement Purification for Logic-Qubit of Photon System Based on Parity Check Measurement Gate.

It has been found that logic-qubit entanglement has great potential for applications in quantum communication and quantum networks in recent years. However, along with the effects of noise and decoherence, the fidelity of the communication transmission can be greatly reduced. In this paper, we investigate the entanglement purification of logic bit-flip error and phase-flip error in polarization logic-qubit entanglement based on the parity-check measurement (PCM) gate, which is constructed by the cross-Kerr nonlinearity and used to distinguish the parity information of two-photon polarization states. The probability of entanglement purification is higher than the scheme using the linear optical method. Moreover, the quality of logic-qubit entangled states can be improved by a cyclic purification process. This entanglement purification protocol will be useful in the future when faced with long-distance communication with logic-qubit entanglement states.

Homogeneous-materials-constructed electromagnetic field concentrators with adjustable concentrating ratio

Based on a two-step linear optical transformation method, a homogeneous-materials-constructed electromagnetic field concentrator whose energy concentrating ratio varies with the incident angle of the electromagnetic wave is proposed. The design is achieved by compressing the space in different directions with different ratios. Numerical simulations are performed to demonstrate the properties, especially the wave-incident angle-dependent concentrating effect of the concentrator. The relationship between the wave-incident angle and the concentrating ratio is investigated and the corresponding analytical expression is given and verified. This wave-incident angle-dependent concentrator constructed with homogeneous materials shows an advantage of facilitating the implementation in practice and provides a convenient route to continuously adjust the concentrated energy density in a pre-defined strategy.

RECIPROCAL INVISIBLE CLOAK WITH HOMOGENEOUS METAMATERIALS

Based on linear optical transformation method, a diamond shaped reciprocal cloak with perfect invisibility in a certain direction is proposed. Compared with traditional cloaks, the object hidden inside the reciprocal cloak is not blind and can receive information from the outer region. Moreover, the reciprocal cloak is constructed of nonsingular homogeneous material parameters with reduced anisotropy that is relatively easy for practical realization. Full wave simulations validate the performance of the cloak.

A linear optical method for measuring the carrier-envelope phase drift

The carrier-envelope offset frequency of a laser oscillator is determined from the visibility of spectrally resolved fringes in a combined two-path multiple-path interferometer. At maximum visibility the pulses have zero carrier-envelope phase drift, while the visibility becomes zero for uncorrelated pulses. The method is widely independent of bandwidth and pulse energy. The effects of carrier-envelope offset phase noise, finite detection time, and dispersion are also discussed.

3-D Physical Motion-Based Bandwidth Prediction for Video Conferencing

Interactive video services such as video conferencing, distance learning, and online video games over the Internet and wireless networks are becoming increasingly prevalent. Because of limited bandwidth on networks and the bandwidth-hungry nature of video, interactive video requires extremely efficient resource management to gain real-time performance. Unlike pregenerated video whose traffic profiles can be computed in advance, efficiency and accuracy of dynamic resource allocation methods for interactive video depend critically on the performance of traffic prediction. Using either traffic data or image features, existing traffic prediction schemes can only provide a short-term traffic prediction. Based on a three-dimensional object's motion, this paper presents a new bandwidth prediction approach for video conferencing. We show that there is a strong correlation between video conferencing traffic and real motion of objects. The real motion can be predicted by the powerful technique Kalman filtering, and the estimated motion is used to make a long-term bandwidth prediction. The new traffic prediction model is tested and compared with the frame-based adaptive normalized least mean square error linear predictor and optical flow-based method with Kalman filtering. Experimental results show that our proposed traffic prediction model achieves much higher accuracy in long-term traffic prediction, which provides the possibility for networks to allocate resources efficiently for video conferencing services.

Step effects on diffusion near a substrate reconstructive phase transition: H on W(100)

We have used the linear optical diffraction method to study the diffusion of hydrogen atoms on flat and stepped W(100) surfaces. At 0.17-monolayer (ML) H coverage, the diffusion coefficient (D) shows a strong anomalous dip at the substrate reconstructive phase transition temperature in an Arrhenius plot for diffusion on both surfaces. No anomalous diffusion behavior is observed at 1.2-ML H coverage on both surfaces in the entire range studied, 240--380 K, consistent with the absence of the phase transition at this H coverage. The strong reduction of D can be attributed to the diverging friction damping near the transition. Steps do not suppress the substrate phase transition and affect the diffusion anomaly very little. For both H coverages, the only effect of steps is to introduce a small Schwoebel-Ehrlich barrier (\ensuremath{\sim}2.2 kcal/mol for 1.2 ML and \ensuremath{\sim}2.8 kcal/mol for 0.17 ML) near the step edges, which slows down H diffusion perpendicular to steps. Measurements of H diffusion parallel to steps reveals no obvious enhancement due to step edge diffusion.

Spectral speckle analysis of resonant secondary emission from solids

A linear optical method to measure coherence and dephasing of excitations in solids is presented. The spectrally resolved degree of coherence of resonantly scattered light is deduced from the intensity fluctuations over its emission directions (speckles). The spectral intensity correlation gives a direct measure of the dephasing rate within the inhomogeneously broadened ensemble. For localized excitons in semiconductor quantum wells, the combination of static disorder, phonon scattering, and radiative decay leads to a spectral dependence of the emission coherence and the dephasing rate, which is well described by model calculations.

Surface diffusion anomaly near a substrate phase transition: H on W(100).

Using a linear optical diffraction method, we have experimentally studied the long predicted diffusion anomalous behavior for H/W(100) near the reconstructive phase transition of the W(100) substrate. This anomaly manifests itself in the form of a strong dip in the diffusion coefficient D at the transition temperature T(C). We interpret the strong reduction of D as a result of the diverging friction damping near the transition. The finite dip in D instead of a vanishing D at T(C) also demonstrates the importance of the non-Markovian (memory) deviation from the simple instantaneous damping picture.

Photoinduced non-linear optical diagnostic of SiN xO y/Si〈111〉 interfaces

Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiN x O y/ Si〈1 1 1〉 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm) . The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10 – 50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiN x O y films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si〈1 1 1〉 –SiN x O y interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50.

Experimental study of surface diffusion rate enhancement along steps: CO on Pt(111)

Surface diffusion of CO parallel to steps on vicinal Pt(111) surfaces has been studied by a linear optical diffraction method. Other than the two normal diffusion channels, namely diffusion over terraces and along step edges, a third channel, which enhances diffusion significantly even at low temperatures, is observed for the first time. The new channel exists only on A- and AB-type stepped surfaces but not on B-type stepped surfaces.

Observation of two diffusion channels in a single diffusion measurement: CO on P-contaminated Pt(111) surface

Resumen We report that, for the first time, two diffusion channels are simultaneously observed on a P-contaminated Pt(111) surface in a single grating smearing measurement via diffusion by a linear optical diffraction method. While the slow channel is accordingly identified as the terrace diffusion, the fast one is identified as diffusion over the phosphorus-contaminated surface regions.

Diffusion of CO on Pt(111) studied by an optical diffraction method

We have measured the diffusion of CO on flat and stepped Pt(111) surfaces using the linear optical diffraction method from an adsorbate grating. Measurements over a wide range of temperatures (133--313 K) and CO coverages (0.1--0.67 ML) indicate Arrhenius behavior with diffusion activation energies of 3.0--4.7 kcal/mol and 7.3--7.9 kcal/mol for flat and stepped surfaces, respectively. Comparisons of our measurements on flat and stepped (defected) surfaces with previous experiments by various groups using various techniques resolves several discrepancies and illustrates the importance of defect-induced effects on variations in measured diffusion parameters.