Analysis Of The Frequency Shift Caused By Inhomogeneous Excitation In Ytterbium Optical Clocks

Present definition of second is based on Cesium microwave clocks. The best Cesium clock can only reach the uncertainty of3.5×10-16. However, optical clocks have already surpassed this record, the uncertainty for Strontium and Hg+optical clocks are1×10-16and1.9×10-17respectively. That makes optical clocks the best candidate for the next generation of frequency standard.Due to Lamb-Dicke effect, cold neutral atoms which loaded in optical lattice, whose first-order Doppler frequency shift and Recoil frequency shift can be suppressed. Lattice induced light shift can be canceled by lattice beams at magic wavelength. At present, black-body radiation shift and collisional shift are the major limitations to optical clocksThis thesis analyzed the mechanism of collisional shift for fermionic clock, calculated the relationship between excitation inhomogeneity and collisional shift, and proposed an experimental scheme for collisional shift suppression.Constrained by Pauli Exclusion Principle, identical fermions could not collide. Initially, spin-polarized fermions are prepared in the same state, if the interrogations are homogeneous, fermions are still indistinguishable could not collide; If inhomogeneity is introduced by the interrogation process, fermions become distinguishable, that will cause collisional shift.Consider a two-particle system, make use of mean-field theory, we got the expression of collisional frequency shift, and introduced the two-body correlation function.According to the experimental results of ytterbium lattice clock, this thesis calculated some important parameters which related to collisional shifts, such as waist radius, lattice depth, transverse and horizontal trapping frequencies, Lamb-Dicke parameters and so on. Defined the inhomogeneity by Rabi frequencies of the two particles, and calculated the range of inhomogeneity for typical experimental conditions. For different values of inhomogeneity, the relationship between collisional shifts and inhomogeneity is calculated.At last, this thesis proposed an experimental scheme for collisional shift suppression.