This paper proposed a new method of small phase shift measurement using frequency-degenerated twin beams. The calculation with semi-classical theory shows: when the frequency degenerated twin beams generated by OPA is injected into M-Z interferometer, the small phase shift measurement beyond SNL can be realized. The minimum detectable phase shift is dependent on the average intensity, the quantum noise level of intensity difference between twin beams and the quantum efficiency of homodyne detection. If intensity difference fluctuation between the quantum correlated twin beams approaches to zero, the minimum detectable phase shift will approach to zero too.
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