Showing papers by "University of Science and Technology of China published in 2000"

Inseparability Criterion for Continuous Variable Systems

Abstract: As with discrete systems, quantum entanglement also plays the basic role in quantum information protocols with continuous variables. A problem of great importance is then to check whether a continuous variable state, generally mixed, is entangled (inseparable). For discrete systems, there is the Peres-Horodecki inseparability criterion [1,2], based on the negativity of the partial transpose of the composite density operator. This negativity provides a necessary and sufficient condition for inseparability of 2 × 2 or 2 × 3 —dimensional systems. In this section, we will describe an entirely different inseparability criterion for continuous variable states, which was first proposed in Ref. [3]. The Peres-Horodecki criterion was also successfully extended to the continuous variable systems shortly afterwards, which will be described in the next section by Simon.

Efficient scheme for two-atom entanglement and quantum information processing in cavity QED

Abstract: A scheme is proposed for the generation of two-atom maximally entangled states and realization of quantum logic gates and teleportation with cavity QED. The scheme does not require the transfer of quantum information between the atoms and cavity. In the scheme the cavity is only virtually excited and thus the requirement on the quality factor of the cavities is greatly loosened.

Novel Single‐ and Double‐Layer and Three‐Dimensional Structures of Rare‐Earth Metal Coordination Polymers: The Effect of Lanthanide Contraction and Acidity Control in Crystal Structure Formation

Abstract: Lanthanide atom sizes (the lanthanide contraction) directly control the type of structure formed by the coordination of a single multidentate ligand, 3,5-pyrazoledicarboxylic acid (H3pdc). Single-layer, double-layer ([Eu2(Hpdc)3(H2O)6], see picture), and three-dimensional networks were found. Control of the reaction pH plays a key role in the structure formation in this system.

Formation Process of CdS Nanorods via Solvothermal Route

Abstract: The formation process of CdS nanorods prepared by the reaction of thiourea and cadmium nitrate in ethylenediamine was investigated in detail by X-ray powder diffraction, transmission electron microscopy, selected-area electron diffraction, and IR techniques. An accordion-like folding process was proposed to account for the formation of CdS nanorods. Further studies indicate that the dissociation of ethylenediamine molecule adsorbed on the surface of CdS results in the formation of CdS nanorods. The obtained CdS single-crystal nanorods showed an abnormal electron diffraction that was explained by the double diffraction of the incident electron inside the sample. The result from electron diffraction confirmed that CdS nanorods grew along c axis.

Probabilistic teleportation and entanglement matching

Abstract: Teleportation may be interpreted as sending and extracting quantum information through quantum channels. In this report, it is shown that to get the maximal probability of exact teleportation through a partially entangled quantum channel, the sender (Alice) need only operate a measurement that satisfies an ``entanglement matching'' to this channel. An optimal strategy is also provided for the receiver (Bob) to extract the quantum information by adopting a general evolution.

Three-dimensional thermoelastic deformations of a functionally graded elliptic plate

Abstract: A new solution in closed form is obtained for the thermomechanical deformations of an isotropic linear thermoelastic functionally graded elliptic plate rigidly clamped at the edges. The through-thickness variation of the volume fraction of the ceramic phase in a metal–ceramic plate is assumed to be given by a power-law type function. The effective material properties at a point are computed by the Mori–Tanaka scheme. It is found that the through-thickness distributions of the in-plane displacements and transverse shear stresses in a functionally graded plate do not agree with those assumed in classical and shear deformation plate theories.

A 3,000-year record of penguin populations

Abstract: There are no historical records of changing penguin populations in the maritime Antarctic1,2. Here we analyse3,4 the concentration of 'bio-elements' in a lake-sediment core dating back approximately 3,000 radiocarbon years. We found that the deposition of penguin droppings had a significant effect on the geochemical composition of the sediment core. Changes in sediment geochemistry reflect fluctuations in penguin numbers and suggest that variations in climate had an impact on penguin populations, which peaked somewhere between 1,400 and 1,800 years ago.

Self-Assembled Nanostructure of a Novel Coil−Rod Diblock Copolymer in Dilute Solution

Abstract: A novel narrowly distributed rod−coil diblock copolymer, poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS), was synthesized by 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated living free radical polymerization. The rodlike PMPCS block is a mesogen-jacked liquid crystalline polymer and is soluble in p-xylene at temperatures higher than 100 °C. When a PS-b-PMPCS dilute solution is cooled, the copolymer chains can self-assemble into a core−shell nanostructure. The temperature-induced self-assembly was studied. We showed, for the first time, that instead of a neutron scattering, a combination of static and dynamic laser light scattering results could also lead to the core radius (Rc) and the shell thickness (ΔR). Using this novel method, we found that when more chains were assembled into the nanostructure, Rc remained as a constant, close to the contour length of the PMPCS block, but the shell became thicker, indicating that the attraction between the insoluble rigid rodlike ...

Optimal entanglement purification via entanglement swapping

Abstract: It is known that entanglement swapping can be used to realize entanglement purification. In this way, two particles belonging to different nonmaximally entangled pairs can be projected probabilistically to a maximally entangled state or to a less entangled state. In this paper, we show, when the less entangled state is obtained, then a maximally entangled state can be obtained probabilistically from this less entangled state if a unitary transformation is introduced locally. The probability of success of our scheme is equal to the entanglement of a single pair purification (if two original pairs are in the same nonmaximally entangled states) or to the smaller entanglement of a single pair purification of these two pairs (if two original pairs are not in the same nonmaximally entangled states). The advantage of our scheme is that no continuous indefinite iterative procedure is needed to achieve optimal purification.

Preparation and phase transformation of nanocrystalline copper sulfides (Cu9S8, Cu7S4 and CuS) at low temperature

Abstract: Nanocrystallites of non-stoichiometric copper sulfides were synthesized via the reaction between [Cu(NH3)4]2+ and thiourea in sealed autoclaves at the low temperature of 60°C for 3 h. Thiourea played a key role in the process of Cu9S8 nanocrystal formation. Through adjusting the redox atmosphere, Cu7S4 and CuS were obtained from the freshly formed Cu9S8 nanocrystals. The products were characterized by means of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy and transmission electron microscopy (TEM) techniques. The Cu ∶ S atomic ratios for Cu9S8 and Cu7S4 were 9 ∶ 8.08 and 7 ∶ 4.05, respectively, analyzed by inductively coupled plasma (ICP) spectroscopy. The possible mechanism of phase transformation among copper sulfides (Cu9S8, CuS, and Cu7S4) was discussed. The optical properties of the products were also recorded by means of UV–vis absorption, and photoluminescence spectroscopy.

Elemental solvothermal reaction to produce ternary semiconductor CuInE2 (E = S, Se) nanorods.

Abstract: A simple and convenient solvothermal process has been developed for the preparation of CuInE2 (E = S, Se) nanorods from the elements in ethylenediamine at 280 °C. Liquid In and the strong capacity of ethylenediamine were found to play important roles in the nanorod growth and electron-transfer process.

Entanglement purification of gaussian continuous variable quantum states

Abstract: We describe an entanglement purification protocol to generate maximally entangled states with high efficiencies from two-mode squeezed states or from mixed Gaussian continuous entangled states. The protocol relies on a local quantum nondemolition measurement of the total excitation number of several continuous variable entangled pairs. We propose an optical scheme to do this kind of measurement using cavity enhanced cross-Kerr interactions.

Preparation and gas-sensing properties of CuFe2O4 at reduced temperature

Abstract: Sol-gel and co-precipitation were used for preparation of copper ferrite. Pure CuFe2O4 was not obtained until 800°C by a sol-gel process, which might be due to the loose contact between copper and iron atoms and the possible low diffusion rate. However, nanocrystalline CuFe2O4 was prepared by a co-precipitation method. The tetragonal CuFe2O4 phase was formed at 90°C. The decomposition of amorphous hydroxides in the dried precipitate continued until 450°C, according to a TG-DTA analysis. Conductance–temperature measurements of the sensor made of CuFe2O4 indirectly indicated that the amount of absorbed oxygen was small, as reflected by the relatively low response. The CuFe2O4 sensors showed a good response to alcohol, which is promising for further development of this type of sensor. The difference in response for various tested gases might be attributed to absorption of reducing gases and reaction between these gases and the absorbed oxygen. It is supposed that the gas-sensing properties of this material might be improved by the addition of catalysts.

Hydrothermal Preparation and Characterization of Luminescent CdWO4 Nanorods

Abstract: CdWO4 nanorods have been prepared through a hydrothermal method at 130 °C. CdWO4 showed very strong photoluminescence at 486 nm at room temperature with the excitation 253 nm. The TEM image of the sample shows that it was composed of monomorphologic nanorods with a size of 80−280 × 20−40 nm2. We investigated the influence of the different initial pH values on the photoluminescent intensity of the products. The results show that the emission intensity is related to the preparation conditions; however, the photoluminescence emission peak positions are independent of the initial conditions.

Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling

Abstract: The coesite-bearing eclogites and associated ultramafic rocks of Bixiling form the largest metamorphic complex in the Dabie–Sulu ultrahigh-pressure (UHP) metamorphic belt. They mainly consist of “fresh” eclogite, kyanite-rich eclogite, retrograded eclogite and garnet peridotite. Fluid inclusion and oxygen isotope studies have been carried out on the different types of eclogite and peridotite in order to identify the role of fluids during the metamorphic evolution culminating in UHP metamorphism. Five types of fluid inclusions were distinguished based on textural criteria and fluid compositions: (1) primary Ca-rich brines in quartz blebs in kyanite; (2) primary NaCl-dominated high-salinity inclusions in omphacite and kyanite; (3) primary NaCl-dominated medium- to high-salinity inclusions in matrix quartz; (4) carbonic inclusions in omphacite and matrix quartz; (5) secondary low-salinity aqueous (or pure water) inclusions in matrix quartz. The Ca-rich fluid inclusions in quartz blebs in kyanite represent the earliest recognizable fluids (prograde metamorphism) as they largely escaped late re-equilibration. Fluid inclusions in omphacite and kyanite may have been trapped during peak metamorphic conditions, whereas low-salinity aqueous inclusions in matrix quartz were trapped during the latest stage of uplift. UV-laser oxygen isotope measurements show that garnet and clinopyroxene from the “fresh” eclogite, kyanite-rich eclogite and garnet peridotite have narrow δ18O values ranging from 3.0 to 3.9‰. In contrast, garnet and omphacite in retrograded eclogite have δ18O values of −1.8 to −1.2 and of −1.1 to −0.6‰, respectively. The difference in oxygen isotope composition is interpreted to result from partial oxygen isotope exchange between the UHP complex and retrograde fluids during late exhumation. Fluids derived from the surrounding gneiss were probably responsible for the low-salinity solutions found in secondary fluid inclusions and the lowering of the δ18O values of the retrograded eclogite.

Synthesis and Characterization of SiC Nanowires through a Reduction−Carburization Route

Abstract: Cubic silicon carbide (3C−SiC) nanowires were synthesized through a reduction−carburization route by using silicon powders and tetrachloride (CCl4) as Si and C sources, and metallic Na as the reductant at 700 °C. The as-prepared SiC nanowires were characterized and studied by X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectra, Raman backscattering, and photoluminescence spectra at room temperature. The SiC nanowires produced from the present route typically have diameters of 15−20 nm and lengths of 5−10 μm. The influencing factors of the formation of the SiC nanowires were discussed and a possible growth mechanism for the SiC nanowires was proposed.