Generation of tripartite Einstein-Podolsky-Rosen steering by cascaded nonlinear process

A scheme is proposed to generate genuine tripartite Einstein-Podolsky-Rosen(EPR)steering in cascaded nonlinear process of the fourth-harmonic generation.The second-harmonic is generated by the first double-frequency process in an optical superlattice.Then,the fourth-harmonic is produced by the second cascaded double-frequency process through quasi-phase-matching technique in the same optical superlattice.The genuine tripartite EPR steering among the pump,the second-harmonic,and the fourth-harmonic beams can be obtained by this cascaded nonlinear process according to a criterion for genuine multipartite quantum steering.The quantum steering properties are discussed by adjusting the parameters related to the cascaded nonlinear system.The present research provides a reference scheme and data for obtaining good multipartite EPR steering in experiment and can advance the applications of quantum steering in the quantum information processing.

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.

Double-port homodyne detection in a squeezed-state interferometry with a binaryoutcome data processing

Performing homodyne detection at a single output port of a squeezed-state light interferometer and then separating the measurement quadrature into two intervals can realize super-resolving and super-sensitive phase measurements,which is equivalent to a binary-outcome measurement.Obviously,the single-port homodyne detection may lose almost part of the phase information,reducing the estimation precision.Here,we propose a data-processing technique over the doubleport homodyne detection,where the two-dimensional measurement quadrature(p1,p2)has been divided into two regions.With such a binary-outcome measurement,we estimate the phase shift accumulated in the interferometer by inverting the output signal.By analyzing the full width at half maximum of the signal and the phase sensitivity,we show that both the resolution and the achievable sensitivity are better than that of the previous binary-outcome scheme.