Spectral Measurement And 1695 Nm Clock Transition Investigation With ¹⁷¹Yb Optical Lattice Clocks

In the past two decades,with advances in precision spectroscopy measurement based on ultra-cold neutral atoms and single trapped ions,the uncertainty and long-term instability of the optical atomic clock have reached the order of low 10^-18,which makes it become the most accurate time-frequency measurement tool in history.Not only has it shown great effects in metrology,definition of the next SI“second”,GPS navigation,and deep-space detection,but it has also shown great application value in the field of basic physics research.The natural linewidth of 41)1)¹⁴66³P₀-41)1)¹³5(9(96²（J=2）transition in ytterbium（Yb）is only a few millihertz,which makes it a potential for high accuracy optical clock.Meanwhile,the transition also has the advantage of the highest sensitivity among atomic clocks to variation of the fine-structure constantα.Combined with the unprecedented accuracy of the optical clock,this high sensitivity opens new perspectives for tests of theories and for searches for new physics,such as tests of the local Lorentz invariance（LLI）and searches for dark matter.Moreover,if the dual clock operation is performed together with the well-established ¹S₀-³P₀ transition in ¹⁷¹Yb,a small variation of the fine-structure constant could be detected.Over the past decade,our group has been committed to the research of ¹⁷¹Yb optical lattice clock and has yielded a great number of positive results.At present,the 41)1)¹⁴66³P₀-41)1)¹³5(9(96²（J=2）clock transition is in the state of study,which is the main content of the thesis.Firstly,the thesis presents some improvements in the 578 nm optical clock system.Cold atoms and clock laser are the core and foundation of the optical clock and are directly related to the further improvement of the clock’s performance.By locking the1112 nm basic-frequency laser and the 1156 nm laser to the same ultrastable optical cavity,the fluctuation of atom number in the optical lattice is greatly reduced.Through the measurement and analysis of the 1156 nm PDH（Pound-Drever-Hall）error signal and the obtained 578 nm clock transition spectrum,it is verified that the frequency stabilization scheme will not affect the stability of the clock laser.This experiment provides a new idea for obtaining a variety of narrow linewidth lasers at the same time.The active residual amplitude modulation（RAM）control scheme is applied to reduce the influence on the frequency stabilization of the clock laser,and fractional frequency instability is constrained within 1×10^-16 which is lower than the thermal noise limit of the optical cavity,which is helpful to build a higher performance clock laser.Secondly,the absolute frequencies of the repumping lasers at 649 nm and 770 nm are precisely determined in an optical lattice,and measured frequencies are more accurate than the previous measurement by one order of magnitude,which provides new data for the field of precision spectroscopy.At the same time,the hyperfine splittings of the ³P₂ and ³S₁ levels are also measured,verifying the relevant theories and experiment results.By optimizing the pumping laser frequency,the normalized excitation fraction of 578 nm transition is improved,and meanwhile,the heating on cold atoms is also avoided by reducing the required repumper’s power,which will contribute to the miniaturization and energy efficiency of optical clocks.Lastly,the study on the forbidden optical transition of the 41)1)¹⁴66³P₀-41)1)¹³5(9(96²（J=2）in ¹⁷¹Yb at a wavelength of 1695 nm is present.This is the first time that the transition is accurately measured experimentally,transition spectra with k Hz-level linewidth are achieved,and the absolute frequency of the transition is also determined.At the same time,the relevant parameters of the transition energy level,such as the magic wavelength,the sensitivity of Zeeman shift,electric dipole（E1）polarizability,hyperpolarizability,and tensor polarizability,are also measured,which provides important data for the relevant theoretical research of atomic physics,and also provides experimental verification for previous theoretical predictions about the clock transition.In addition,the scheme that further narrows the linewidth of the clock transition spectra to the hertz level is theoretically discussed,and the experimental solution is also proposed.This work will prompt us to understand and study the 1695nm clock transition further,and lay a foundation for the achievement of hertz-level 1695nm transition spectra and the operation of the ¹⁷¹Yb optical clock with dual frequencies in the near future.