Magnetic Fiels Stabilization And RF Fields Manipulation Of Cold ~6Li Atom Interferometry

With the development of cold atom technology,atom interferometry with its precision and versatility plays an important role in the field of precision metrol-ogy.Since the advent of the first light pulse interferometry in 1991,it has been widely applied to inertial sensing,measurements of gravity,the fine structure constant,gravitational red shift,the Newtonian gravitational constant,verify the equivalence principle,etc.Since lithium is the lightest quality among alkali metal elements,its recoil frequency is larger than that of alkali atoms such as ru-bidium and sodium,and it can get the same measurement accuracy in a shorter integral time,this is a natural advantage and research value in atomic interfer-ence measurement.In 2017,M¨uller’s group reported the~7Li atom interferometry,this lays the foundation for future verification of the equivalence principle by the isotope~6Li-~7Li with the largest relative mass difference.While there were no re-ports about~6Li cold atom interferometry,therefore,we launched research on~6Li atomic interferometry,providing possibilities for verifying equivalent principles by the isotopic~6Li-~7Li atomic interferometry.Due to~6Li having unresolved excited-state hyperfine structure,there is no magnetic insensitivity state of|m_F=0（?）because~6Li has half-integer total an-gular momentum,the preparation of the state is difficult,and it is sensitive to magnetic fields and requires magnetic field stabilization,so this paper mainly studies based on these difficulties and the following innovative research results have been achieved:（1）Design a magnetic field locking system,which realizes the stability of the current noise of the magnetic field coil by shunting the current noise of the magnetic field coil.In this paper,a magnetic field locking system is used to real-ize a 2.27 ppm level locking,compared with unlocking,the low-frequency noise of the current has been suppressed by more than 45d B.To evaluate the stability of the actual magnetic field,the Rabi oscillation of~6Li atoms was measured by using atoms as magnetic field probes,and the coherence time of~6Li atoms was increased by 9.6 times,effectively extending the coherence time of the system.The Raman loss spectrum of atoms was measured,and the system locking accu-racy was further verified by counting the fluctuations of atomic numbers at the inflection point of Gaussian inclination of the loss spectrum:The RMS noise of the magnetic field was suppressed to 1.2m G at 528G,the magnetic field noise was suppressed by 16 times,and the relative uncertainty was 2.27ppm,providing a stable and accurate background magnetic field for cold atomic gases.And to increase the universality of this magnetic field locking system,we have locked the MOT magnetic field and the compensating magnetic field and achieved a locking effect of 96 times and 68 times respectively achieving a locking effect of nearly two orders of magnitude.（2）Based on magnetic shielding theory and finite element analysis,we com-bine the actual spatial position limitations,optical access,and electrical circuit requirements to design a magnetic shield box for the plug-in structure,which minimizes magnetic leakage.The magnetic shielding efficiency was measured by changing the applied magnetic field,and the shielding efficiency was 28,which is similar to our simulation results.To obtain a more stable magnetic field,the surrounding magnetic field environment is optimized,and the compensation coils are powered by low-noise current sources.In the end,a magnetic field environ-ment with magnetic field noise is better than 50μG at 150m G,which provides a stable magnetic field environment for the~6Li cold atomic interferometry.（3）For the~6Li atom,a high-efficiency magnetic sub-level state preparation method for the~6Li cold atom interferometry is proposed.The atoms are effi-ciently prepared to the magnetic sub-level state of interest by the interaction of RF and 323 nm laser.We designed the RF antenna according to the antenna principle and built the RF antenna system.Finally,the measured state prepara-tion efficiency was 94%by the Raman spectroscopy after the state preparation,which greatly inhibited the decoherence caused by multi-interference paths,and significantly improved the contrast of interference fringes.