Optical and defect properties of S-doped and Al-doped GaSe crystals

S-doped and Al-doped GaSe crystals are promising materials for their applications in nonlinear frequency conversion devices. The optical and defect properties of pure, S-doped, and Al-doped GaSe crystals were studied by using photoluminescence（PL） and Fourier transform infrared spectroscopy（FT-IR）. The micro-topography of（0001） face of these samples was observed by using scanning electron microscope（SEM） to investigate the influence of the doped defects on the intralayer and interlayer chemical bondings. The doped S or Al atoms form the SSe^0 or AlGa^＋1） substitutional defects in the layer GaSe structure, and the positive center of AlGa-^＋1 could induce defect complexes. The incorporations of S and Al atoms can change the optical and mechanical properties of the GaSe crystal by influencing the chemical bonding of the layer structure. The study results may provide guidance for the crystal growth and further applications of S-doped and Al-doped GaSe crystals.

Editorial: Advances in Optical Techniques for Mechanical Measurements

Recently, optical techniques have attracted great attention due to their excellent non-destructive, non-contact, high-resolution, and full-field characteristics. Applications can be found in diverse fields such as precision mechanics and manufacturing, aerospace and automotive testing and inspection, materials science, and biomedical engineering. Advances in Optical Techniques for Me- chanical Measurements presents the latest research progresses in several widely used optical techniques with applications in preci- sion mechanical engineering.

Dependence of Nitrogen/Argon Reaction Gas Amount on Structural,Mechanical and Optical Properties of Thin WNx Films

WNxfilms are deposited by reactive chemical vapor deposition at different amounts of nitrogen in gas mixtures.Experimental data demonstrate that nitrogen amount has a strong effect on microstructure, phase formation,texture morphology, mechanical and optical properties of the WNxfilms. With increasing nitrogen a phase transition from a single WNxphase with low crystallinity structure to a well-mixed crystallized hexagonal WNxand face-centered-cubic W2N phases appears. Relatively smooth morphology at lower N2concentration changes to a really smooth morphology and then granular with coarse surface at higher N2concentration. The SEM observation clearly shows a columnar structure at lower N2concentration and a dense nanoplates one for higher nitrogen content. The hardness of WNxthin films mainly depends on the film microstructure. The absorbance peak position shifts to shorter wavelength continuously with increasing nitrogen amount and decreasing particle size.

Evolution of a Thermo Vacuum State in a Single-Mode Amplitude Dissipative Channel

We investigate how an initial thermo vacuum state, in the context of thermo field dynamics, evolves in a single-mode amplitude dissipative channel, and find that in this process the thermo squeezing effect decreases while the fictitious-mode vacuum becomes chaotic.

Six-State Quantum Key Distribution Using Photons with Orbital Angular Momentum

A new implementation of high-dimensional quantum key distribution （QKD） protocol is discussed. Using three mutual unbiased bases, we present a d？level six-state QKD protocol that exploits the orbital angular momentum with the spatial mode of the light beam. The protocol shows that the feature of a high capacity since keys are encoded using photon modes in d-level Hilbert space. The devices for state preparation and measurement are also discussed. This protocol has high security and the alignment of shared reference frames is not needed between sender and receiver.

Preparation of Arbitrary Four-Qubit W State with Atomic Ensembles via Rydberg Blockade

The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme （PRA 79, 022304） has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity （F - 0.994） via our scheme.

Relation between Characteristic Function of Density Operator and Tomogram

In terms of the intermediate coordinate-momentum representation （Chin. Phys. Lett. 18 （2001） 850） and using the technique of integration within an ordered product of operators, we put the tomography theory into operator version. We reveal the new relation between the tomogram and the characteristic function of the density operator. The new expansion of the density operator in terms of the intermediate coordinate-momentum representation is also obtained.

Preparation of Cluster States of Atomic Qubits in Cavity QED

We propose an optical scheme to generate cluster states of atomic qubits, with each trapped in separate optical cavity, via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degenerate ground states of the atom, hence the entanglement between them is relatively stable against spontaneous emission. A single-photon source and two classical fields are employed in the present scheme. By controlling the sequence and time of atom-cavity-laser interaction, we show that the atomic cluster states can be produced deterministically.

Cryptanalysis and Improvement of Quantum Secret Sharing Protocol between Multiparty and Multiparty with Single Photons and Unitary Transformations

In a recent paper [Yan F L et al. Chin.Phys.Lett. 25（2008）1187], a quantum secret sharing the protocol between multiparty and multiparty with single photons and unitary transformations was presented. We analyze the security of the protocol and find that a dishonest participant can eavesdrop the key by using a special attack. Finally, we give a description of this strategy and put forward an improved version of this protocol which can stand against this kind of attack.

Implementing a Multi-Qubit Quantum Phase Gate Encoded by Photonic Qubit

A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time remains unchanged with the increasing number of qubits. In addition, the influence of cavity decay and atomic spontaneous emission on the gate fidelity and photon loss probability is also discussed by numerical calculation.

Modeling and Simulation of MOEMS Gyroscope Based on TE-TM Mode Converter

A novel structure design of micro optic electro mechanical system（MOEMS）gyroscope is presented in this paper.The structure combining surface acoustic wave（SAW）sensor,optical waveguide diffractive component,electro-optical modulator etc.is integrated on a LiNbO3 substrate as the gyroscope for sensing rotating angular velocity,and an optical readout device is added on the traditional SAW typed TE-TM mode converter as the detecting device.The principles of the MOEMS are discussed in the paper,and simulation result shows that there would be apparent advantages of higher precision and stronger anti-vibration capacity.

Quantum Swap Gate with Molecular Ensembles via Cavity Quantum Electrodynamics

We present a simple method to realize a swap gate at one step with two molecular ensembles in a stripline cavity. In this scheme, we can benefit from the enhancement of the coherent coupling and acquire a long coherent time with encoding qubits in different spin states of the rotational ground state in the molecular ensembles. As a by-product, a scheme to create an entangled state with one excitation stored in two ensembles is proposed.

Tripartite Entanglement via Microwave Driven Atomic Coherence

We propose a new scheme to achieve the tripartite entanglement based on the standard criteria [Phys. Rev. A 67（2003） 052315] in a inverse-tripod atomic system. In our scheme, the atomic coherence is introduced by two microwave fields which drive the upper three levels of atom. By numerically simulating the dynamics of system, we investigate the generation and evolution of entanglement in the presence of atom and cavity decay. As a result, the present research provides an efficient approach to achieve fully tripartite entanglement with different frequencies and initial states for each entangled mode, which may have impact on the progress of multicolored multi-notes quantum information networks.

A Wavelength-Tunable Fiber-Coupled Narrow-Band Twin-Photon Source

We present a wavelength-tunable narrow-band fiber-coupled source to generate correlated photon pairs at 539 nm and 1550nm. Using a lO-mm PPLN crystal, we obtain more than 50ram tunable range near 1550nm. This source, given its spectral property and tunable property, is well suited for tasks in fiber-optic quantum communication and cryptography networks.

Universal Quantum Cloning Machine in Circuit Quantum Electrodynamics

We propose a scheme for realizing the 1 → 2 universal quantum cloning machine （UQCM） with superconducting quantum interference device （SQUID） qubits in circuit quantum electrodynamics （circuit QED）. In this scheme, in order to implement UQCM, we only need phase shift gate operation on SQUID qubits and the Raman transitions. The cavity number we need is only one. Thus our scheme is simple and has advantages in the experimental realization. Furthermore, both the cavity and the SQUID qubits are virtually excited, so the decoherence can be neglected.

General Theory of Decoy-State Quantum Cryptography with Dark Count Rate Fluctuation

The existing theory of decoy-state quantum cryptography assumes that the dark count rate is a constant, but in practice there exists fluctuation. We develop a new scheme of the decoy state, achieve a more practical key generation rate in the presence of fluctuation of the dark count rate, and compare the result with the result of the decoy-state without fluctuation. It is found that the key generation rate and maximal secure distance will be decreased under the influence of the fluctuation of the dark count rate.

Changchun Institute of Optics and Fine Mechanics and Physics of CAS

Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP) of CAS was established in Changchun, Jilin Province, on July 5, 1999 on the basis of consolidation of two former CAS institutes: Changchun Institute of Optics and Fine Mechanics, and Changchun Institute of Physics. The institute is an experimental unit of CAS Knowledge Innovation Program (KIP).

Modeling the rail surface unevenness of a high-precision radio telescope

This study proposed a coarse-fine mixed model for describing the rail surface unevenness of an ultra-large fully steerable radio telescope （Qi Tai Telescope） with a diameter of 110 meters. The rail surface unevenness includes information on error arising from two different scales, i.e., the long-period- short-change and the short-period-long-change. Consequently, in this study an idea of a mixed model was proposed, in which trigonometric and fractal functions were, respectively, used to describe infor- mation on error from two scales. Key parameters were determined by using the least squares method and the wavelet transform method, and finally, a specific mathematical expression of the model was obtained by optimization. To validate the effectiveness of the new modeling method, the mixed model was then used to describe the rails of the Green Bank Telescope, the Large Millimeter Telescope, and a radio telescope in Miyun, Beijing. A comparative study revealed that the maximum error was less than 15 %, thus the result was superior to those of existing modeling methods.

Optical and Mechanical Properties of Polyurethane/Surface-modified Nanocrystalline Cellulose Composites

in order to improve the optical and mechanical performances of waterborne polyurethane （WPU）, nanocrystalline cellulose （NCC）/WPU composites were synthesized in this study. NCC （prepared by acid hydrolysis of cotton fiber） was modified by （3-aminopropyl）triethoxysilane （APTES） to enhance its compatibility with WPU, and the surface-modified NCC was characterized by grafting ratio, crystallinity and contact angle （CA）. NCC/WPU composites were examined by scanning electron microscopy （SEM）, X-ray powder diffraction （XRD） and thermogravimetric analysis （TG）. The anti-yellowing property, specular gloss, pencil hardness, and abrasion resistance of NCC/WPU composites were investigated by the methods of Chinese National Standards GB/T 23999-2009, GB/T 9754-2007, GB/T 6739-2006 and GB/T 1768-2006, respectively. The results showed that the grafting ratio of NCC modified by 6% APTES was 36.01% and the crystallinity of modified NCC was decreased with the enhancement of APTES. CA of the modified NCC was decreased by 28.8% and the nanoparticles were homogeneously dispersed in the WPU matrix. The XRD patterns of the NCC/WPU composites were relatively steady, while the thermal stability of the composites was enhanced by 6.7% with 1.0 wt% modified NCC. Modified NCC affected the specular gloss of NCC/WPU composites more obviously than the anti-yellowing property. The pencil hardness of NCC/WPU composites was increased from 2H to 4H by addition of NCC and the abrasion resistance of the composites was enhanced significantly. In general, NCC/WPU composites showed significant improvements in the optical and mechanical performances.

The Study on the Mechanical Properties of Optical Fiber With Long-Term Time Aging

The fiber properties depending on the coating thickness and long-term time aging were investigated. The coating strip forces of optical fiber were strongly increased with secondary coating thickness. But it did not change with time aging up to 90 days. The tensile strength and stress corrosion parameters of coated fiber were increased with time aging also but the increasing rate was quite different depending on the coating