Quantum Fisher information and spin squeezing in one-axis twisting model

We investigate the dependence of the average parameter estimation precision （APEP）, which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state ｜θ0,φ0〉 in a one-axis twisting model. Jin et al. [New J. Phys. 11 （2009） 073049] found that the spin squeezing sensitively depends on the polar angle θ0 of the initial coherent spin state. We show explicitly that the APEP is robust to the initial polar angle θ0 in the vicinity of π/2 and a near- Heisenberg limit 2IN in quantum single-parameter estimation may still be achieved for states created with the nonlinear evolution of the nonideal coherent spin states θ0- π/2. Based on this model, we also consider the effects of the collective dephasing on spin squeezing and the APEE

Three-Dimension Parametric Simulation of Knitted Fabric Based on the Twisted Loop Model

To enhance the realistic simulation effect of knitted fabric,a new three-dimension( 3D) twisted loop model was proposed. This model was constructed by using Non-uniform Rational B-Spline( NURBS) surface. The control points of this surface were generated through rotating the cross-section along the center path of yarn. The cross-section of yarn was generated based on the two-level hexagonal close packing model. Both of the center path and the cross-section were fitted by NURBS. With this twisted loop model,3D parametric simulation of knitted fabric was realized in 3DS MAX by utilizing MAXScript and analyzing the relationships between structure parameters( including the wale-spacing, the course-spacing,the yarn diameter,and the fabric thickness) and geometric model. The simulation of knitted fabric has 3D realistic twist effect clearly. Furthermore,the structure parameters and the twist parameters of fabric can be modified interactively.

Optimal phase sensitivity of atomic Ramsey interferometers with coherent spin states

We present a detailed analysis of phase sensitivity for a nonlinear Ramsey interferometer, which utilize effective mean-field interaction of a two-component Bose-Einstein condensate in phase ac- cumulation. For large enough particle number N and small phase shift φ, analytical results of the Ramsey signal and the phase sensitivity are derived for a product coherent state θ, 0）. When collisional dephasing is absent, we confirm that the optimal sensitivity scales as 2/N3/2 for polar angle of the initial state θ = π/4 or 3π/4. The best-sensitivity phase satisfies different transcendental equations, depending upon the initial state and the observable being measured after the phase accumulation. In the presence of the collisional dephasing, we show that the N-3/2-scaling rule of the sensitivity maintains with spin operators jx and jy measurements. A slightly better sensitivity is attainable for optimal coherent state with θ = π/6 or 5π/6.