Total Evaluation Of The Cold Ytterbium Atomic Clocks And Study Of The Moving Optical Lattice

The atomic frequency standards have played an important role in the navigation,precision measurement,and basic physics researches.Stabilized frequency of the laser at the corresponding atomic transition is a revolutionary advance in the development of atomic frequency standards.In recent decades,the performance of the optical clock has been greatly improved,many of the world's research groups have built optical clocks performing better than the cesium atomic frequency standard.As a result,the optical clock is expected to become the next generation of time and frequency standards.There are two main kinds of optical clocks,one is ionic optical clock and another one is neutral atomic optical clock.The frequency uncertainty and instability of these two kinds optical clocks have reached 10-18 magnitude,while the main difference between the two types optical clocks is the atom number interrogated in the experimental cycle.For ionic optical clock,which confined single-ion in the quadruple trap.On the contrary,neutral optical clocks trapped thousands of atoms in the optical lattice.Therefore,the frequency fluctuation caused by quantum project noise can be suppressed efficiently.Realized a more accurate optical clock will promote the development of other scientific research areas,such as providing better quantum state control,new methods of quantum science,as well as breaking the limitation of basic constant measurements and a new method for relativity measurement.Two figures of merit that described the quality of the optical clocks are instability and systematic uncertainty.Instability is the statistical accuracy of the optical clocks and systematic uncertainty is the sum of the system measurement offsets.Nearly a decade,the State Key Laboratory of Precision Spectroscopy and Department of Physics in East China Normal University has been working on two ytterbium optical clocks Yb-1 and Yb-2.This thesis introduces the research process and evaluates of two ytterbium optical clocks in East China Normal University.Firstly,we optimized the experimental parameters of Zeeman slow and second stage cooling.We measure the dependence of the atomic fluorescence signal on the laser detuning,light intensity and magnetic field current.Then,we carefully optimized the second stage cooling,and achieve the dependence of the cold atom temperature,atom number and density on the second stage cooling laser detuning,intensity and MOT(Magneto-Optical-Trap)magnetic field gradient.According to the experimental results,we selected suitable parameters for our experiment.Finally we obtained ultracold atoms,which is approach to the Doppler limit temperature of this transition.Then the cold atoms are loaded into optical lattice for clock spectrum interrogation.Secondly,we measured the “magic wavelength” of the ytterbium atomic clock by changing the frequency and intensity of the lattice laser.We analyzed the light shift in 171 Yb optical clock,and get the correction value and frequency uncertainty by experimental measurement.Both the frequency and power fluctuation of lattice laser caused the change of the clock transition frequency,therefore,we lock the frequency to a Fabry Perot(FP)cavity with Pound-Drever-Hall(PDH)technique and stabilized the laser power.In the experiment,we obtained the lattice laser introduced frequency uncertainty in 10-16 magnitude,and the clock laser induced in 10-18 magnitude.The lattice laser induced frequency uncertainty is mainly caused by inaccurate measurement of the frequency by the wavemeter,thus improve the measurement accurate can reduce the uncertainty to 10-17 magnitude.Thirdly,we experimental measured the first order Zeeman shift,second order Zeeman shift and collisional frequency shift of the ytterbium optical clock.In order to eliminate the first order Zeeman shift,we adding a bias magnetic field to make the clock transition energy level occurs Zeeman splitting.By interrogating the twop transitions in the clock-transition spectrum the first Zeeman shift canceled.However,due to the external residue magnetic field,there is still a second order Zeeman shift,which cannot be eliminated.To evaluate the Zeeman shift,we monitoring the fluctuation of the background magnetic field with a high resolution magnetometer and changing the current of the bias magnetic field during the experiment.The collision shift is caused by atom collisions,so we can vary the atom number to evaluate it.The total systematic uncertainty of the ytterbium optical clock is 1.88×10-16.By analyzing the experimental results,which provides a reference for the further optimization of the optical clock system.Finally,in order to effectively suppress the blackbody radiation frequency shift,we proposed a moving lattice scheme in this text.At present,there are two main methods to reduce the blackbody radiation shift,one is measure the temperature around the atoms in the vacuum chamber accurately,while the other one is to reduce the temperature of the chamber and the impact of the ambient temperature on atoms.In this paper,we control the atoms and move them into a cryogenic chamber for clock transition spectrum interrogation,and the lattice moved about 4 mm.In addition,we theoretical analyzed the moving lattice and realized in the experiment.According to the experimaental results,provide the bsis for the improvement of the experimental setup.