音频段连续变量压缩态光场探测系统的研究

The stable, high-level squeezed states of light has generated great interest in the gravitational wave community as a means for improving the quantum-noise-limited performance. To the confidently measure these squeezed states, it is first necessary to measure the shot-noise at audio-band frequencies and below. However, due to the limitation of various conditions in the actual measurement at audio-band frequencies, such as the LO intensity noise of the balanced homodyne detection, and the electronics noise of the detector, which are adverse to characterizing the squeezed state at audio-band frequencies. On the basis of the theory background of the balanced homodyne detection (BHD), we analyze quantitatively the influence of the LO intensity noise and the common mode rejection ratio (CMRR) of BHD on the measured squeezing degree, which is very important to quantify the requirements of the CMRR of the detection for measuring the squeezing audio-band frequencies and inferring the real squeezing level. In the experiment we can reduce the impact of the the LO intensity noise by improving the CMRR audio-band frequencies. Also, in order to improve the ability to resist interference of the detector, the input current noise of the BHD at audio-band frequencies is analyzed, and the electronics noise is reduced through effective means. Ultimately, with the parameters of lower electronics noise and higher CMRR, the BHD at audio-band frequencies is designed and manufactured.

稳定的高压缩度的连续变量压缩态光场作为提高引力波探测精度的一种重要手段，其检测频率一般在音频段。然而在音频段连续变量压缩态光场的压缩度测量受到种种限制，诸如平衡零拍探测系统中音频段本地振荡光强度噪声远大于量子噪声极限的限制，音频段探测器电子学噪声大的限制等，都将造成实际测量的结果不能如实反映压缩态的真实水平。申请人欲定量分析音频段Local光强度噪声和探测系统共模抑制比对测量压缩度的影响，从而为音频段平衡零拍探测系统的共模抑制比提出“度”的要求，实验上，从光学和电学两部分入手提高探测系统的共模抑制比来对抗音频段Local光的强度噪声；并通过对平衡零拍探测器在音频段的输入电流总噪声进行分析，采取有效措施来降低电路的电子学噪声，从而提高探测器的音频抗干扰能力。最终设计一款适用于音频段的低噪声、高共模抑制比的平衡零拍探测系统。

连续变量压缩态光场作为精密测量和量子信息处理的重要资源，已被广泛应用于引力波探测，构建纠缠态光场实现量子传输、量子秘钥分发、量子通信和产生cluster态实现通用量子计算等方案，在实验和应用中不仅需要产生高压缩度的压缩态光场，同时准确测量压缩度同等重要。针对压缩光的产生和测量多集中在射频段（~MHz），原因是射频段光的经典噪声较小，系统噪声容易达到量子噪声极限，量子噪声易于测量。在用于引力波探测的迈克耳孙干涉仪或弱磁场检测等实验中，其检测频率一般在音频段（20 Hz - 20 kHz），传统的射频探测系统一方面要受到环境中机械振动、音频段光束的抖动、电路的1/f噪声，电磁等因素的干扰；另一方面由于在音频段激光的强度噪声远大于量子噪声极限，要实现直接探测压缩态光场的量子噪声，需要抑制各种声频噪声，降低各种机械振动,尤其是来自电子学噪声的干扰。平衡零拍探测系统是一种有效探测音频量子噪声的手段，由于平衡零拍探测系统高共模抑制比的特点，能够有效对抗由于弛豫震荡引起的音频处本地振荡光的强度噪声。本项目在实验上，从光学和电学两部分入手提高探测系统的共模抑制比。首先优化探测系统光学部分，即尽量保证光平衡后，其次提高探测器内两支路（包括两光电二极管及电子元件）的平衡，即提高探测器部分的共模抑制比。为了制作性能优良（信噪比更高）的探测器，基于自减平衡零拍探测器电路和光电二极管的等效电路，定量分析在音频段各部分噪声源在总输入噪声中所占的比重；实验上，首先通过选取低噪声的交流跨阻运算放大器来降低电子学噪声，其次根据理论分析结果，通过采用合适电路有针对性地进一步降低电子学噪声。总之，通过对平衡零拍探测器在音频段的输入电流总噪声进行定量分析，通过选取优良的跨阻抗运算放大器和采用合适的电路来降低系统的电子学噪声，最终制作出适用于音频段的低噪声、高共模抑制比的连续变量压缩态光场的探测设备。