用于冷原子的高精度磁场锁定系统  

High-precision magnetic field locking system for cold atoms

作　　者：刘雪梅 芮扬 张亮[1] 武跃龙 武海斌[1] Liu Xue-Mei;Rui Yang;Zhang Liang;Wu Yue-Long;Wu Hai-Bin(State Key Laboratory of Precision Spectroscopy,East China Normal University,Shanghai 200241,China)

机构地区：[1]华东师范大学,精密光谱科学与技术国家重点实验室,上海200241

出　　处：《物理学报》2022年第14期175-181,共7页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2017YFA0304201);国家自然科学基金(批准号:11925401,11734008,12074125);上海市优秀学术带头人(批准号:17XD1401500);上海市基础研究重大研究计划(批准号:17JC1400500)资助的课题.

摘　　要：磁场调控的Feshbach共振是调控原子间相互作用最常用的基本工具,减小磁场起伏,对于提高超冷原子散射共振的稳定性有着重要意义.本文通过一套分流磁场锁定系统,实现了百高斯磁场下相对不确定度为10^(-6)量级的磁场锁定,相较于未经锁定时,低频电流噪声得到45 dB以上的抑制.利用本文的锁定方法,^(6)Li原子团Rabi振荡相干时间提高了9.6倍,有效延长了超冷原子系统的相干时间.同时根据原子的Raman损耗谱标定了磁场均方根噪声,通过选择无相互作用的528 Gs(1 Gs=10^(-4) T)处进行检测,磁场均方根噪声抑制到1.2 mGs,相较于未经锁定时,磁场均方根噪声降低16倍,磁场锁定相对不确定度为2.27×10^(-6).这样的磁场锁定系统,可以为超冷原子气体提供精确稳定的背景磁场,对延长量子存储寿命、精确调控原子散射、开展凝聚态物理模拟等超冷量子气体实验有重要意义.In ultracold atomic experiments,evaporative cooling is usually achieved by using Feshbach resonance magnetic fields on the order of Gauss to hundreds of Gausses.The frequency of resonant transition induced by the optical field or radiofrequency is directly affected by the stability of the quantum axis.For example,the phase between two linearly independent vectors of a qubit is affected by the magnetic field noise.Based on the Feshbach resonance technique,magnetic field regulation has become a basic tool to control the interaction between atoms.Narrow Feshbach resonance shows unique advantages in high-temperature superconducting,superfluidity,neutron star state simulation,etc.However,since its resonance width and Fermi energy can be compared with each other,the scattering characteristics are greatly disturbed by the magnetic field.Therefore,a stable and uniform magnetic field is a prerequisite for studying the narrow Feshbach resonances.In experiment,Helmholtz coils are usually used to provide the magnetic field for cold atomic gas,and the magnetic field noise is generally determined by the coil current noise and other magnetic field noises of the environment.However,there are relatively few researches of the high-precision control of large magnetic fields above hundreds of Gausses.With a larger coil current required,the coil current noise contributes more to the magnetic field noise,thus high-precision control of large magnetic fields is still challenging.In this paper,a magnetic field locking system is used to realize a 2.27×10^(-6) level locking of the Feshbach magnetic field.A feedback locking system is used to achieve the stability by shunting the magnetic field coil current noise.Compared with the non-locked magnetic field,the low-frequency current noise is suppressed by more than 45 dB.To assess the stability of the actual magnetic field at the atoms,the Rabi oscillation is measured,the coherence time increases nearly 9.6 times,which effectively improves the stability of the ultracold atomic system.Further

关 键 词：磁场锁定 FESHBACH 共振 超冷量子气体 

分 类 号：O56[理学—原子与分子物理]