Preliminary Stability Evaluation And Application Of The Transportable Strontium Optical Clock

Development of high-performance optical atomic clock has an important influence on precision measurement,satellite navigation,fundamental research,etc.Compared with ion clocks,optical clocks based on neutral atoms have an advantage that more atoms can be interrogated simultaneously,such that the signal to noise ratio of the measured clock signal can be greatly improved.With great improvement of the optical clocks,the SI second probably would be redefined in the future.As one of the main requirements for this redefinition,the repeatability of frequency measurements of the optical clocks must be considered.Development of transportable optical clocks makes the comparison between two remote optical clocks get rid of the distance limit.Besides,transportable optical clocks also have significant applications in research of relativistic geodesy,metrology,space optical clock,etc.The Nation Time Service Center has conducted series of works on development and evaluation of the stationary strontium optical lattice clock.On the other hand,a transportable strontium optical clock is being in the development stage.To make the whole system easy to disassemble and move,there are some important technical issues that need to be addressed in developting the transportable optical clock based on the research of the stationary optical clock,such as reduction of the system size,modularized construction of the subsystems,centralized monitoring of the hardware equipments,etc.And some important operating parameters need to be practically evaluated to improve the performance of the transportable optical clock.In this dissertation,we collate the works conducted on the preliminary stability evaluation and application of the transportable clock system.The main contents are as follow:1. A transportable ⁸⁷Sr atomic optical lattice clock is constructed using the miniaturized physical system and the modularized optical systems.Based on analysis of the energy level structure of most alkaline earth atoms,we utilize a Zeeman slower to slow down the atomic velocity.And the temperature of the strontium atoms is decreased to 4.45μK via two-stage laser cooling.After that the strontium atoms are loaded into the optical lattice formed by two counterpropagating lasers with wavelength of 813 nm.2. An experimental scheme is proposed to construct the control system of the transportable strontium optical clock using the multifunctional acquisition cards,which is helpful to realize centralized management and real-time control of the hardware equipments.Some important technical parameters of the clock system are derived from the measurement outcomes of the sideband spectrum,the degenerated spectrum,the Zeeman spectrum,and the polarized spectrum.After closed-loop operation,via time-interleaved self-comparison,we obtain the self-comparison stability of the clock system as a function of the detection timeτ,which is expressed deviation declines to 6.3×10^-17.These results identify the clock’s measurement capability on systematic frequency shifts and corresponding uncertainty.3. A theoretical study is presented about the repumping efficiency’s effect on parameters measurement of ultracold atoms trapped in optical lattice.Based on the measured carrier spectrum,the repumping efficiency is derived as 0.703.Using the theoretical model to fit the sideband lineshape and the Rabi flopping data,we obtain the longitudinal and the transverse temperature of the trapped ⁸⁷Sr atoms as 3.82μK and 5.27μK,respectively.And the Rabi frequency and the misalignment angle of the interrogation laser are evaluated as 9.64 Hz and 6.9 mrad,respectively.The calculated results provide a reference for optimizing the atomic cooling system.4. Based on the strontium experimental platform,we propose a dual-entropy-source quantum random number generation method.We use a modulation system to convert the coherent beam’s photon number fluctuations into the frequency fluctuations and impose them on the pump light.Considering characteristics of atomic spontaneous emission in phase-defusing field,we directly measure the fluorescence intensity fluctuations and extract quantum random signals from the measured noises.Besides,using the same device,we experimentally demonstrate a method for parallel quantum random number generation,and analyze the self-correlation and mutual correlation properties of the output sequences.The experimental results can be applied in Monte Carlo simulation of the physical processes in developing optical atomic clocks.