利用频率简并的孪生光束进行亚散离粒噪声极限的精密测量

We use the semi-monolithic nondegeneration optical parametric amplifier (NOPA) to decrease the heat effect coming from pump laser, so that the stability of NOPA is improved. When the infrared seed wave was injected into cavity and the temperature of crystal was controlled precisely, the resonance of two down-conversion modes in cavity was ensured. The equency-degenerate and polarization-nondegeneration bright EPR (Einstein-podolsky-Rosen) beams with the correlation of amplitude quadrature and the anticorrelation of phase uadrature has been obtained by the process of arametric amplification. The measurement system consisted of polarization beam splitter was designed. By using the interference measurement between local light and the squeezed vacuum state of EPR beams, the quantum correlation 0.85 of EPR beams were obtained. Then bright EPR beams with the anticorrelation of amplitude quadrature and the correlation of phase quadrature was produced through the process of parametric deamplification. The degree of it's quantum correlation is 0.58. By tuning the frequency of pump laser continuously, the twin beams whose frequency can be tuned continuously were obtained. Based on this, combining the frequency modulation spectrum technology, the measurement of absorption spectrum with high sensitivity for Cs2 was realized. The improvement of the signal to noise ratio relative to the shot noise limit (SNL) is 4dB. Our experiment provides a new physical tool for the measurement of absorption spectrum with high sensitivity beyond SNL.

理论和实验研究表明，强度相关的孪生光束可用于超高精度的光学测量和微弱信号检测，信噪比可突破标准量子噪声的极限。本项目首先通过非简并的孪生光束，再通过偏振及相移测量装置实现亚散粒噪声极限的精密测量。其目的是探索用强度差压缩光进行相敏测量的有效途径，建立一套完善的测量装置。