Evaluations Of The Blackbody Radiation Shift In Strontium Optical Lattice Clock

At present,ultra-high precision and stability optical clocks are widely used in applications such as dark matter detection,general relativity verification,measurement of basic physical constants,gravitational wave detection,measurement of gravitational potential,quantum calculations,and multi-body physics research.The optical clock is not only widely used in basic applied scientific research,but also plays an increasingly important role in many frontier scientific fields.Although the current definition of "second" is based on the 133Cs fountain clock,the optical lattice clock of neutral atoms has a very low shot noise limit by capturing and detecting thousands of atoms at a time,its uncertainty and instability is 2 orders of magnitude higher than the 133Cs fountain clock,which is a strong competitor for the definition of the next generation "seconds".Due to capturing and detecting thousands of atoms at one cycling,optical lattice clock based on neutral atoms has a very low shot noise limit,and is one of the most promissing competitor for the next generation of definition of the second.The optical lattice clock based on Fermi strontium is one of the earliest proposed and studied optical lattice clocks.The process of realization the 87Sr optical lattice clock includes the preparation of the quantum reference system,closed-loop operation and frequency measurement by femtosecond laser-frequency comb techniques.The preparation of the quantum reference system includes the first stage of cooling,the second stage of cooling,optical lattice loading,and the preparation of stretched states.The atomic number obtained by the first stage of cooling is 2.3 × 107,and the temperature is 5 mK.The atomic number obtained by the second stage of cooling is 3.5 × 106,and the temperature is 3.9 ?K.The number of atoms loaded into the optical lattice is 104,and the lifetime is about 1.6 s.The frequency of the clock laser is locked to the clock transition frequency by bimodal peaks locking,and the instability reaches 5×10-17 after closed-loop operation about 3000 seconds.The frequency shift caused by blackbody radiation is one of the dominate correction during the evaluation of the optical lattice clock.The blackbody radiation shift is mainly affected by ambient temperature.For the strontium atomic optical clock experimental apparatus of the National Time Service Center,the uncertainty of the blackbody radiation frequency shift is evaluated by the theoretical analysis,measurement the temperature of the vacuum cavity outer surfaces and software simulation.The thermal radiation of the system is mainly induced from the atomic oven,the sapphire window,and the Zeeman slower device,and as well as the influence of the room temperature.The real-time temperature of five different points on the outer surface of the vacuum cavity is monitored and recorded with five calibrated platinum resistances while the system is running normally.Model of vacuum cavity was established by using the SolidWorks.The method of finite element analysis is used to simulate the variation of the temperature around atom samples.The result shows that the temperature around atoms is vary with the temperature of the vacuum cavity.When the temperature of the ambient temperature changes by 0.72 K,the fluctuation of the temperature around the atoms is 0.34 K.Finally,the total correction of blackbody radiation of the system is evaluated to be-2.13(1)Hz,and the correction uncertainty is about 2.4×10-17.