Optical Frequency Standard Based On A Single Trapped Aluminum With An Uncertainty Of 3E-18

In the past few decades,the optical frequency standard has developed rapidly,and its frequency stability and uncertainty have surpassed that of the cesium atomic fountain clock,which is the reference for the current definition of ’second’.In 2026,the 28th International Conference on Weights and Measures will reconsider a new definition of the second,in which the optical clock with higher accuracy will be a candidate for the new definition of the second.Meanwhile,high-precision optical clocks have a wide range of applications in the field of quantum precision measurement,such as the measurement of the fine structure constant α,verification of relativistic effects,and gravitational wave detection.In addition,high-precision optical clocks also play an important role in metrology and satellite navigation.The 27Al+ ion is the best optical clock in the world in terms of systematic uncertainty,reaching 9.4 × 10-19,due to its advantages such as insensitivity to electromagnetic fields and blackbody radiation.Different from the existing 25Mg+-27Al+ion optical clock research,we innovatively adopt 40Ca+ion as the auxiliary ion.The advantages of this scheme are as follows:firstly,the Doppler cooling limit of 40Ca+ ion is lower;secondly,the energy level structure of 40Ca+ion can carry out electromagnetically induced transparent cooling,which cools the ion to vibrational ground state for all secular motion modes and effectively suppresses the secular motion frequency shift of the optical clock;finally,the S1/2?D5/2 electric quadrupole clock transition of 40Ca+ ion can diagnose the electromagnetic field environment of the ion trap,leading to a more accurate assessment of the systematic uncertainty of the aluminum ion optical clock.The work performed in this dissertation is outlined as follows:1.A40Ca+-27Al+quantum logic optical clock system was completely built,mainly including a single ion trap physics system,a laser-cooled optical system,and an ion and optical clock control system.2.A study on the rapid loading of 40Ca+-27Al+ion pairs was carried out.By investigating the ablation laser power and period,ion loading angle,and sympathetic cooling process that affect ion loading,and optimizing the ion loading program,a fast loading of 40Ca+-27Al+ ion crystals was achieved based on pulsed laser ablation and sympathetic cooling,which improved the loading time of 27Al+ ion from about 26 min previously to about 1 min.This study provides a prerequisite for the subsequent longterm operation of the 27Al+ ion optical clock and provides a solution for other groups investigating sympathetic cooling experiments to improve ion loading efficiency.3.Sympathetic EIT cooling of the 40Ca+-27Al+ion pair was achieved.All six secular motion modes of the 40Ca+-27Al+ ion pair were cooled to the vibrational ground state.The average phonon numbers of each mode were:nxcom=0.15±0.02,nxstr=0.12±0.03,nycom=0.15±0.02,nystr=0.13±0.02,nzcom=0.15±0.02,nzstr=0.09±0.01.After EIT cooling,the fractional secular motion frequency shift and uncertainty is(2.2±0.2)×10-18 for 80 ms interrogation time.With the EIT cooling scheme,the secular motion frequency shift uncertainty,which limited the previous uncertainty of our aluminum ion optical clock system,was reduced from 3.1×10-18 to 2×10-19.4.The second-order Zeeman frequency shift uncertainty of aluminum ion optical clock was reduced from 6.4×10-18 to 4×10-19 by the scheme of reducing the bias magnetic field.5.The.clock transition line of 40Ca+-27Al+ ion optical is detected as well as closedloop locking were achieved.The stability of the optical clock was evaluated by a selfcomparison scheme with a stability of 3.1×10-15/(?).Subsequently,each error term of the optical clock was evaluated with a total systematic uncertainty of 3.1×10-18.