无自旋交换弛豫条件下自旋投影噪声的研究

Spin exchange relaxation free (SERF) magnetometer is the most sensitive magnetic sensor, with many important applications in both fundamental research and practical field. So far the sensitivity of SERF magnetometer has approached the quantum limit of the spin projection noise. To improve the sensitivity of SERF magnetometer further, the spin projection noise must be studied in more details. The common method of studying the spin projection noise is parametric Faraday rotation spin noise spectroscopy(SNS). In order to avoid large 1/f technical noise in the low frequency region, a constant bias magnetic field is often applied. However, SERF can only be achieved near zero field, the common method is not suitable for SERF. In the project, a new method to study the spin noise under SERF condition is proposed. Byπpulse modulating the magnetic field appropriately, the SNS signal is shifted to higher Larmor frequency, and thus the 1/f technical noise is avoided. Besides, the field between the pulses is zero, therefore the SERF condition is satisfied. By this method, we are promising to get the SNS in SERF, and study experimentally the mechanism of spin exchange relaxation to spin projection noise. At the same time, by using the state diffusion model we hope to further get the analytical form of the mechanism of spin exchange relaxation to spin projection noise.

基于无自旋交换弛豫（SERF）原理的原子磁力仪具有极高的灵敏度，因而在科学研究和国民经济等诸多领域有着广泛而重要的应用。目前SERF磁力仪的灵敏度已经逼近自旋投影噪声的量子极限，若要进一步提高SERF磁力仪的灵敏度就必须对自旋投影噪声做更深入的研究。通常研究自旋投影噪声的方法是利用顺磁法拉第旋光自旋噪声光谱。为避开低频处巨大的1/f技术噪声，自旋噪声光谱实验通常要加一个较大外磁场，而SERF成立的条件是要维持nT级别的外磁场，因此这种方法并不适合SERF情况。本项目提出了一种π脉冲调制磁场的方法，能够维持高频调制以避开低频处的1/f技术噪声，同时在两次脉冲磁场之间外磁场为零，满足SERF条件。通过这种方法，我们有望观测到SERF成立条件下的自旋噪声光谱，从而实现自旋交换弛豫对自旋投影噪声作用机制的实验研究。同时利用态扩散模型方法，我们将进一步给出自旋交换弛豫对自旋投影噪声作用机制的解析形式

基于无自旋交换弛豫（SERF）原理的原子磁力仪因其极高的灵敏度正受到越来越多的关注和研究。目前SERF磁力仪的灵敏度已经逼近自旋投影噪声的量子极限，若要进一步提高SERF磁力仪的灵敏度就必须对自旋投影噪声做更深入的研究。基于上述考虑，本项目研究了在无自旋交换弛豫成立条件下的自旋投影噪声光谱。首先，通过研究SERF磁力仪加深了对无自旋交换弛豫现象的理解。随后，搭建实验平台实现了一种π脉冲调制磁场的方法，不仅能够将信号调制到高频，避开低频处的1/f技术噪声，而且在两次脉冲磁场之间使得外磁场为零，满足SERF条件。利用这种方法，我们实验上观测到了在SERF成立条件下的自旋投影噪声光谱。然后通过改变脉冲磁场参数，进而改变自旋交换弛豫速率，研究了无自旋交换弛豫条件对自旋投影噪声光谱的线宽，高度以及面积等特征的影响。最后，利用Wiener-Khintchine理论，结合π脉冲磁场特征和自旋交换弛豫的影响，给出了自旋投影噪声光谱的解析形式，解释了测得的自旋投影噪声光谱的基本特征。