Frequency tunable continuous variable （CV） entangled optical beams are experimentally demonstrated from a non-degenerate optical parametric oscillator working above the threshold.The measured correlation variances of amplitude and phase quadratures are 3.2 and 1.5 dB,respectively,below the corresponding shot noise level （SNL） in the tuning range of 580 GHz （2.25 nm）.The frequency tuning is realized by simply controlling the temperature of the nonlinear crystal.
The influence of the extra classical noises in seed beams on the entanglement between the signal and the idler modes of the output fields generated by a non-degenerate optical parametric amplifier operating at deamplification is investigated theoretically and experimentally. With the increase of the extra classical noises in the seed beams, the correlation degree of the output entangled optical fields, which is scaled by the quantum noise limit, decreases rapidly. The experimental results axe in good agreement with the theoretical calculations.
The preparation of multipartite entangled states is the prerequisite for exploring quantum information networks and quantum computation.In this paper,we review the experimental progress in the preparation of cluster states and multi-color entangled states with continuous variables.The preparation of lager scale multipartite entangled state provide valuable quantum resources to implement more complex quantum informational tasks.
