Branching spin chain dynamics

We study the dynamics of various branched spin chain systems. In such systems entanglement can be generated and distributed, providing an essential resource for teleportation or distributed quantum processing. We show in detail how simple operations can be employed at chosen times to change the subsequent dynamics of the branched spin chains, rendering the distributed entanglement more accessible.     

Base doping and dopant profile control of SiGe npn and pnp HBTs

Incorporation of high doping concentrations and the creation and maintaining of steep doping profiles during processing are key enabler for high level RF performance of heterojunction bipolar transistors (HBTs). In this paper, we discuss results of base doping and dopant profile control for npn and pnp SiGe HBTs fabricated within 0.25 μm BiCMOS technologies. High level of electrically active B and P doping concentrations (up to 10²⁰ cm⁻³) have been incorporated into SiGe. By adding C to SiGe steep doping profiles have been maintained due to the prevention of dopant diffusion during device processing. It is shown that broadening of P doping profiles caused by segregation could be reduced by lowering the deposition temperature for the SiGe cap. B and P atomic layer doping is shown to be suitable for the creation of steep and narrow doping profiles. This result is demonstrating the capability of the atomic layer processing approach for future devices with critical requirements of dopant dose and location control.     

Corrosion behavior and protective ability of Zn and Zn-Co electrodeposits with embedded polymeric nanoparticles

The anodic behavior, corrosion resistance and protective ability of Zn and alloyed Zn-Co (∼3 wt.%) nanocomposite coatings were investigated in a model corrosion medium of 5% NaCl solution. The metallic matrix of the layers incorporates core-shell nano-sized stabilized polymeric micelles (SPMs) obtained from poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block co-polymers. The protective properties of the composite coatings were evaluated using potentiodynamic polarization technique, polarization resistance measurements and powder X-ray diffraction. The sizes and distribution of the stabilized polymeric micelles in the starting electrolytes used as well as in the metal matrices of the layers were investigated using scanning and transmission electron microscopy. The results obtained are compared to those of electrodeposited Zn and Zn-Co (∼3 wt.%) alloy coatings at identical conditions and demonstrate the enhanced protective characteristics of the Zn nanocomposites during the investigating period. The influence of the SPMs on the corrosion resistance of the nanocomposite layers is commented and discussed.     

Synthesis and tribological behaviors of diamond-like carbon films by electrodeposition from solution of acetonitrile and water

Diamond-like carbon (DLC) films were prepared on silicon substrates by liquid phase electrodeposition from a mixture of acetonitrile and deionized water. The deposition voltage was clearly reduced owing to the presence of deionized water in the electrolyte by changing the basic properties (dielectric constant and dipole moment) of the electrolyte. Raman spectra reveal that the ratio of sp³/sp² in the DLC films is related to the concentration of acetonitrile. The surface roughness and grain morphology determined by atomic force microscopy are also influenced by the concentration of the acetonitrile. The UMT-2 universal micro-tribometer was used to test the friction properties of the DLC films obtained from electrolytes with different concentration. The results convey that the DLC film prepared from the electrolyte containing 10 vol.% acetonitrile has the better surface morphology and friction behavior comparing with the other. In addition the growth mechanism of the film was also discussed.     

Entanglement in One-Dimensional Random XY Spin Chain with Dzyaloshinskii--Moriya Interaction

The impurities of exchange couplings, external magnetic fields and Dzyaloshinskii-Moriya （DM） interaction considered as Gaussian distribution, and the entanglement in one-dimensional random XY spin systems is investigated by the method of solving the different spin-spin correlation functions and the average magnetization per spin. The entanglement dynamics at central locations of ferromagnetic and antiferromagnetic chains have been studied by varying the three impurities and the strength of DM interaction. （i） For the ferromagnetic spin chain, the weak DM interaction can improve the amount of entanglement to a large value, and the impurities have the opposite effect on the entanglement below and above critical DM interaction. （ii） For the antiferromagnetic spin chain, DM interaction can enhance the entanglement to a steady value. Our results imply that DM interaction strength, the impurity and exchange couplings （or magnetic field） play competing roles in enhancing quantum entanglement.     

Quantum State Transfer between Charge and Flux Qubits in Circuit-QED

We propose a scheme to implement quantum state transfer in a hybrid circuit quantum electrodynarnics （QED） system which consists of a superconducting charge qubit, a flux qubit, and a transmission line resonator （TLR）. It is shown that quantum state transfer between the charge qubit and the flux qubit can be realized by using the TLR as the data bus.     

A Hyperchaotic Attractor Coined from Chaotic Lü System

We report a new hyperchaotic attractor coined from the chaotic Lü system by using a state feedback controller. Theoretical analyses and simulation experiments are conducted to investigate the dynamical behaviour of the proposed hyperchaotic system     

Remote Generation of Entanglement for Individual Atoms via Optical Fibres

The generation of atomic entanglement is discussed in a system that atoms are trapped in separate cavities which are connected via optical fibres. Two distant atoms can be projected to Bell-state by synchronized turning off of the local laser fields and then performing a single quantum measurement by a distant controller. The distinct advantage of this scheme is that it works in a regime where Δ≈κ〉〉g, which makes the scheme insensitive to cavity strong leakage. Moreover, the fidelity is not affected by atomic spontaneous emission.     

Entangled Radiation through an Atomic Reservoir Controlled by Coherent Population Trapping

We show that it is possible to generate Einstein-Podolsky-Rosen （EPR） entangled radiation using an atomic reservoir controlled by coherent population trapping. A beam of three-level atoms is initially prepared in nearcoherent population trapping （CPT） state and acts as a long-lived coherence-controlled reservoir. Four-wave mixing leads to amplification of cavity modes resonant with RabJ sidebands of the atomic dipole transitions. The cavity modes evolve Jnto an EPR state, whose degree of entanglement is controlled by the intensities and the frequencies of the driving fields. This scheme uses the long-lived CPT coherence and is robust against spontaneous emission of the atomic beam. At the same time, this scheme is implemented in a one-step procedure, not in a two-step procedure as was required in Phys. Rev. Lett. 98 （2007） 240401.     

Quasi-Random Resistor Network Model for Linear Magnetoresistance of Metal--Semiconductor Composite

A new model for the linear magentoresistance (MR) of the Ag_2+δSe and Ag_2+δ Te thin films is proposed. The thin film is considered as a metal--semiconductor composite and dispersed into an N×N quasi-random resistor network. The network is constructed from four-terminal resistors and the mobility of carries μ within the network has a quasi-random distribution, i.e. a Gaussian distribution with two constraint conditions. The model predicts that the MR increases with the increasing magnetic fields, and increases linearly at high field. Moreover, the MR decreases with the increasing temperatures. A good agreement between the theoretical MR and the available experimental data is found.