从一个压缩真空态中减去一个光子是制备光学薛定谔猫态的一种有效方法。研究表明,通过这种方法制备的薛定谔猫态的保真度依赖于压缩态光场的纯度。利用一个抽运光部分共振的非简并光学参量放大器实验制备了纯度为0.993 的双模压缩态。由于热效应的存在，非简并光学参量放大器在较宽的抽运功率范围内能够获得纯度较高的双模压缩态。

Subtracting a photon from a squeezed vacuum state is an efficient method for preparing an optical Schr?dinger cat state. It is shown that the fidelity of the Schr?dinger cat state based on photon subtraction depends on the purity of squeezed vacuum state. A two-mode squeezed state of light with a purity of 0.993 is experimentally produced by a non-degenerate optical parametric amplifier, where the pump beam oscillates partially in the cavity. Especially, two-mode squeezed states with high purity can be obtained by the non-degenerate optical parametric amplifier in a wide range of pump power due to the presence of thermal effect.