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The bright two-color tripartite entanglement is investigated in the process of type II second harmonic generation (SHG) operating above threshold. The two pump fields and the second harmonic field are proved to be entangled, and the dependence of the entanglement degree on pump parametersigma and normalized frequency Omega is also analyzed.

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Widely frequency tunable bright sub-Poissonian field preparation has been experimentally achieved with quantum-correlated twin beams in the continuously variable regime. The noise of the sub-Poissonian field is reduced to more than 2 dB below the shot-noise level throughout the entire wavelength-tunable range of 7.4 nm. A maximum noise reduction of 45% (2.6 dB) is observed. The statistical distribution of a sub-Poissonian field is also obtained.

In recent continuous-variable (CV) multipartite entanglement researches, the number of fully inseparable light modes has been increased dramatically by the introduction of a multiplexing scheme in either the time domain or the frequency domain. In this paper, we propose a scheme that a large-scale (≥ 20) CV dual-rail cluster entangled state is established based on a spatial mode comb in a self-imaging optical parametric oscillator, which is pumped by two spatial Laguerre-Gaussian modes with different polarization and identical frequency. A sufficient condition of full inseparability for a CV dual-rail cluster entangled state is used to evaluate the degree of quantum entanglement. It is shown that entanglement exists over a wide range of analyzing frequency and pump parameter. We have found a new scheme that uses the optical parametric cavity to generate a large-scale entanglement based on optical spatial mode comb. The presented system will be hopefully as a practical entangled source for quantum information.