Preliminary Research On The Ytterbium Optical Clock With A 3D Optical Lattice

The high-precision clock is not only a key technology in the field of time service and timekeeping,global positioning and navigation,but also has important applications in basic research fields such as precision measurement physics.With the development of the optical frequency standards,the time and frequency measurement has been entering a new stage.A lot of research groups in different countries are competing to develop optical clocks in order to possess enough speaking right in the time and frequency measurement and related fields in the future.¹⁷¹Yb atomic optical clock,as one of the most mature and best-performing optical clocks in the world,has shown great value in research and application.The ¹⁷¹Yb optical clock with the best performance in the world is developed by NIST,of which the instability has reached the order of 10^-19.In the process of improving the performance of the optical clock to the order of 10^-18,collision shift has been one of the main limiting factors.How to effectively reduce the impact need to be carefully considered in the experiment.For neutral atomic optical clock,a large number of atoms in the lattice can been detected at the same time,making the quantum projection noise greatly suppressed,which allows the stability of the optical clock to decrease more rapidly.However,the interaction between the atoms trapped in the optical lattice will cause the clock frequency shift,and the resulting collision frequency shift becomes an important factor limiting the performance improvement of the optical clock.In order to reduce the impact of collision frequency shift,theoretically,there need to have a less atoms in the optical lattice to reduce the interaction between atoms.However,it conflicts with the need for more atoms to improve the stability of the optical clock.In order to overcome this contradiction,an effective scheme is to construct a Fermi degenerate three-dimensional optical lattice to load the atoms,realizing that each site only own a single atom,thereby eliminating the interaction between atoms.In this paper,based on the one-dimensional optical lattice clock of ¹⁷¹Yb atoms,the specific experimental schemes will be given on how to realize the three-dimensional optical lattice clock with ¹⁷¹Yb atoms.The ultimate performance of the clock can be then estimated.Firstly,we briefly introduce the current development background,current status and some problems which were encountered by the optical clock.At the same time,we introduce the ¹⁷¹Yb one-dimensional optical lattice clock in our group.We deduce some basic theories of the optical lattice,and evaluate the effects of lattice shift and collision shift.Then,based on the JILA ⁸⁷Sr three-dimensional optical lattice clock,we introduce the basic theories of the Fermi degenerate three-dimensional optical lattice,including cooperative evaporative cooling,Hubbard model and Mott insulation state.In the three-dimensional optical lattice clock,by preparing the Mott insulation state each site loaded with only one atom,which can effectively suppress the collision shift in the optical lattice.As for the three-dimensional optical lattice,the experimental schemes and the calculation of lattice shifts are complicated.However,since the nuclear spin of ¹⁷¹Yb is1/2,its lattice tensor shift is naturally zero,which will greatly simplify the experimental setup,and is also a major advantage of the ¹⁷¹Yb optical lattice clock over the Sr optical lattice clock.By using linearly polarized lattice light and alternately detecting±1/2magneton energy level transition,the vector shift can be effectively suppressed,and it will eventually contain only the scalar lattice shift.Finally,a specific experimental scheme is given on how to realize a ¹⁷¹Yb Fermi degenerate three-dimensional optical lattice clock.After a two-stage MOT cooling,the atoms are loaded into a crossed optical dipole force trap?FORT?of a far-detuning 532nm laser.In order to realize the preparation of the ¹⁷¹Yb Fermi degeneracy,we can adjust the scattering length by the orbit Feshbach or cooperative evaporation cooling.At the same time,the scheme of realizing three-dimensional optical lattice clock with ¹⁷³Yb atoms is also analyzed.Then,the preparation scheme and detection methods of Mott insulation state are discussed.Subsequently,the magnitude and uncertainty of the lattice shift and collision shift in the three-dimensional optical lattice clock of ¹⁷¹Yb atoms are estimated,which are at most on the order of 10^-18.This paper lays a theoretical foundation for future implementing a ¹⁷¹Yb three-dimensional optical lattice.