Cold Atom Interferometer Of ~6Li And Precision Measurement Of Recoil Frequency

Atom interferometer is of great significance in the field of basic physics and applied physics.It is an indispensable tool for measuring the internal struc-ture and external field information of atoms.Owing to the ultraprecise sensing in metrology,in basic physics research,an atom interferometer has been used to measure gravitational constant,test the equivalence principle and verify the standard model.Atom interferometer also plays an important role in the applied physics field,where they have been used to measure a small change in gravity,and to detect the Earth’s tides and metal deposits beneath the surface.With its small mass,lithium has a natural advantage in precision measurement.Due to its recoil frequency being 20 times that of rubidium,the relative accuracy can be improved by 20 times compared with the rubidium atom interferometer if un-der the same systematic error.In 2017,the Berkeley team implemented the⁷Li atom interferometer,but the⁶Li atom interferometer has not been implemented because of many challenges.However,we realized the⁶Li atom interferometer for the first time,which filled the gap.Since the upper level of⁶Li atom is unsolved,it is difficult to use laser cooling.The total angular momentum of⁶Li is not an integer,there is no mag-netic insensitive transition with|m_F=0?→|m_F=0?.These greatly increase the difficulty of realizing the atom interferometer.In this thesis,we mainly use323nm narrow linewidth cooling to obtain the atom sample with the low temper-ature that breaks through the recoil temperature limit;using the method that combined 323nm light and RF to realize state preparation,nearly 90%of the atoms are prepared in the state|2?(|2S_1/2,F=1/2,m_F=-1/2?);the Raman transition of the magnetic insensitive configuration is realized by usingσ⁺-πconfiguration and the interference time was greatly extended;the first⁶Li cold atom interferometer was realized,and the recoil frequency was measured,and the following innovative research results were mainly obtained:（1）We lock the light of the 2S→3P ultraviolet transition to the optical frequency comb,and obtain frequency instability is less than 1Hz.According to the characteristics that the natural linewidth of ultraviolet transition compared with the recoil frequency,the narrow linewidth cooling technology is used.We obtained the atom sample that broke through the recoil temperature limit and realized the transfer of 671nm MOT to 323nm MOT.（2）Two perpendicular Raman beams are used to realize theσ⁺-πtransition of state|2?and state|5?(|2S_1/2,F=1/2,m_F=-1/2?→|2S_1/2,F=3/2,m_F=+1/2?).The sensitivity to the magnetic field of this configuration can be com-pared with the magnetic insensitive transition of the⁷Li|m_F=0?→|m_F=0?transition.We get the magnetic insensitive Raman transition with⁶Li which the total angular momentum is half-integer.Compared with the magnetic sensitive configuration by using state|2?and state|4?(|2S_1/2,F=1/2,m_F=-1/2?→|2S_1/2,F=3/2,m_F=-1/2?),the interference time is increased from 0.4ms to 2.3ms,which greatly improves the interference time and the measurement accuracy.（3）We develop a homemade RF antenna with a standing wave loss ratio of 1.1.By using the combined action of 323 nm light and RF,we achieve high-efficiency state preparation of the sublevel and nearly 90%of the atoms are prepared to the state|2?.（4）The first⁶Li atom interferometer was realized,and an interference signal with an interference contrast of 0.13 was obtained.By measuring the recoil fre-quencies in four different effective momentum directions,the angle of the Raman beams was corrected,and finally,the recoil frequency of⁶Li is 2π×73672.789（36）Hz,and the fine-structure constant is 1/137.035976（33）.In this thesis,the⁶Li cold atom interferometer has been realized for the first time,and the interference signal with 2.3ms is obtained by using the magnetic insensitive Raman transition.The recoil frequency is measured at the same time,and its accuracy is nearly two orders of magnitude higher than that of the⁷Li atom interferometer.The implementation of⁶Li cold atom interferometer fills the international gap,lays an important foundation for the equivalence principle test by the isotope of⁶Li-⁷Li,which have the maximum relative mass difference.At the same time,it enriches the elements for the measurement of fine-structure constant,combined with large momentum transfer technology,which is expected to improve the highest accuracy at present.