铷原子气体自旋噪声谱测量的信噪比分析

摘要

Spin noise spectroscopy is a non-demolition technique to detect the spin dynamics,and it is a good way to realize spin property under thermal equilibrium.Since spin noise arises from spin fluctuation at thermal equilibrium,it is a weak signal,therefore,various methods are used to enhance the signal-to-noise ratio (SNR) of the measurement system.To study the influence from different factors on the quality of spin noise spectroscopy,we report spin noise spectroscopy measurements in Rubidium vapor with three methods:a commercial frequency analyzer,a data acquisition card (DAC) with fast Fourier transform (FFT) done by a computer,and a DAC with real-time FFT based on FPGA (field-programmable gate array),respectively.According to the experimental results,we discuss several parameters and their influences on the SNR of the spectrum,including spectrum accumulation time,measurement efficiency and acquisition resolution.We find that the accumulation time is the most important factor for achieving high-quality spectrum.Measurement efficiency indicates how a good quality of the spin noise spectroscopy can be achieved in afinite time period,and we make a comparison of measurement efficiency among three methods.However,improvement of acquisition resolution does not make much more contribution to the quality of spin noise spectroscopy.Taken all into account,the DAC with real-time FFT performs best due to its bigger data utilization ratio,higher measurement efficiency and the multiplex advantage,thus it is more helpful for spin noise spectroscopy measurement in the study of spin dynamics.%自旋噪声谱是一种非扰动的自旋动力学研究方法,通过探测系统在非激发条件下的自旋涨落,可以揭示系统在热平衡状态下的性质.因为系统在稳态下的自旋涨落十分微弱,所以提高信噪比在自旋噪声谱的测量中特别重要.本文采用频谱仪、数据采集卡和实时傅里叶变换采集卡三种方法来测量铷原子气体的自旋噪声谱,并将实验结果进行对比,分析了叠加次数、测量效率和采样深度等因素对谱线信噪比的影响.实验发现,谱线叠加次数对自旋噪声谱的信噪比影响最为显著,测量效率则能反映不同方法在相同的测量时间内得到的谱线质量,并比较了三种方法的测量效率,采样深度的提高并不能明显改善自旋噪声谱的信噪比.相比于传统的频谱仪和数据采集卡,实时傅里叶变换采集卡的数据利用率和测量效率更高,从而具有更好的信噪比,非常有利于自旋噪声谱在自旋动力学研究中的应用.