| In recent years,with the development of cold atom and ultra-stable laser technology,the uncertainty and stability of optical clocks have been greatly improved,reaching the level of 10-18 or even better,which far exceeds the current definition of seconds based on the Cs fountain clock.Therefore,high-precision optical clocks have become one of the best candidates for the definition of the next generation of seconds in the future.In addition,high-precision optical clocks can also be used in the elevation difference measurements,precise measurement of physical constants,detection of dark matter and so on.An optical clock based on single trapped 40Ca+ ion shows significant advantages on its relatively simple laser scheme,which all the required lasers can be realized by commercially available semiconductor lasers.Moreover,the natural linewidth of the 40Ca+ ion’s clock transition is only 0.14 Hz.So the 40Ca+ion is very suitable for the development of transportable optical clocks.The research during my Ph.D.study focuses on optical clock based on single trapped 40Ca+ ion.Two 40Ca+ ion optical clocks have been built to experimental demonstrate the measurement of elevation difference based on optical clocks.A new clock comparison measurement method based on quantum correlation spectroscopy has also been proposed to improve the frequency stability.The main results are outlined as follows:1.A transportable calcium ion optical clock(TOC-729-3)system was built,including an ion trapping and detection system,laser frequency stabilization and optical systems.In addition,another set of transportable calcium ion optical clock(TOC-729-1)optical system has been upgraded to meet the requirements of the high-precision comparison experiment of the two optical clocks.Based on the ARTIQ controlling software system,the experimental programs of two clocks have been developed using Python language for realizing sub-automatic running functions.And a comparison experiment with Rabi detection spectroscopy method and Ramsey detection spectroscopy method by a probe time of 60 ms was carried out,which corresponds clock frequency stability as 4.8×10-15/(?)and 3.6×0-15/(?)respectively.2.The experimental demonstration of elevation difference measurement was realized using two transportable calcium ion optical clocks in the lab,each of them with systematic shift uncertainty at the level of 1.3×10-17.The elevation differences measurement results were-0.83(21)m,0.05(21)m and 1.02(21)m respectively,which are consistent with the geometrically measured results within the predicted error range.After correcting the systematic frequency shifts(including the gravitational redshift),the relative frequency difference between the two transportable optical clocks was measured as-0.7(2.2)×10-17,verifying the reliability of transportable calcium ion optical clocks at the low level of 10-17.3.Using two transportable calcium ion optical clocks,a quantum correlation spectroscopy measurement experiment beyond laser coherence was realized successfully.Firstly,the quantum correlation spectroscopy was realized on two calcium ions trapped in the TOC-729-1 system,and the ion coherence time was measured as 827(252)ms,which surpassed the laser coherence time.Secondly,based on two independently transportable calcium ion optical clocks,the quantum correlation spectroscopy was realized with a 200 ms probing time by using a clock laser with only ms-coherence time level,and the frequency comparison measurement stability was measured to be 4.0×10-15/(?),which beyond the limitations of laser coherence.(the stability has been improved more than 43 times compared to using traditional Ramsey detection spectroscopy at a probing time of 1ms using an ms-level coherence laser). |
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