Effective sideband cooling in an ytterbium optical lattice clock

Sideband cooling is a key technique for improving the performance of optical atomic clocks by preparing cold atoms and single ions into the ground vibrational state. In this work, we demonstrate detailed experimental research on pulsed Raman sideband cooling in a $^{171}$Yb optical lattice clock. A sequence comprised of interleaved 578 nm cooling pulses resonant on the 1st-order red sideband and 1388 nm repumping pulses is carried out to transfer atoms into the motional ground state. We successfully decrease the axial temperature of atoms in the lattice from 6.5 μK to less than 0.8 μK in the trap depth of 24 μK, corresponding to an average axial motional quantum number $\langle n_z\rangle<0.03$. Rabi oscillation spectroscopy is measured to evaluate the effect of sideband cooling on inhomogeneous excitation. The maximum excitation fraction is increased from 0.8 to 0.86, indicating an enhancement in the quantum coherence of the ensemble. Our work will contribute to improving the instability and uncertainty of Yb lattice clocks.     

Realization of Green MOT for Ytterbium Atoms

We report the experimental realization of a magneto-optical trap （MOT） of ^174 Yb atoms operating on the ^1 So -^3 P1 intereombination transition at 555.8nm. The green MOT is loaded by a Zeeman-slowed atomic beam. In order to increase the capture velocity of the MOT, we use the trapping laser beams consisting of five discrete frequency components obtained by modulating the laser light through an electro-optic modulator. The trapped atomic number of the ^174Yb isotope is about 6.2 × 105, and the temperature of the cold atomic cloud is estimated to be about 100μK. The success of the green MOT is an clock. important step towards the goal of an ytterbium optical     

A robust method for frequency stabilization of 556-nm laser operating at the intercombination transition of ytterbium

A frequency-stabilized 556-nm laser is an essential tool for experimental studies associated with 1 S 0-3 P 1 intercombination transition of ytterbium (Yb) atoms.A 556-nm laser light using a single-pass second harmonic generation (SHG) is obtained in a periodically poled MgO:LiNbO 3 (PPLN) crystal pumped by a fiber laser at 1111.6 nm.A robust frequency stabilization method which facilitates the control of laser frequency with an accuracy better than the natural linewidth (187 kHz) of the intercombination line is developed.The short-term frequency jitter is reduced to less than 100 kHz by locking the laser to a home-made reference cavity.A slow frequency drift is sensed by the 556-nm fluorescence signal of an Yb atomic beam excited by one probe beam and is reduced to less than 50-kHz by a computer-controlled servo system.The laser can be stably locked for more than 5 h.This frequency stabilization method can be extended to other alkaline-earth-like atoms with similar weak intercombination lines.     

Maximized cooling efficiency for a Zeeman slower operating at optimized magnetic field profile

We build a Zeeman slower with consecutive coils and use it to load an Yb magneto-optical trap(MOTs).Cooling efficiency is measured by the fluorescence intensity of the atomic cloud trapped by the MOT.An optimized magnetic field profile can acquire the maximum cooling efficiency,corresponding to a good compromise between the smaller magnetic field mismatch and the high capture velocity.Our studies provide useful information on how the performance of the Zeeman slower can be improved.     

Precise calibration of zero-crossing temperature and drift of an ultralow expansion cavity with a clock transition spectrum

We report a clock transition spectrum approach, which is used to calibrate the zero-crossing temperature and frequency drift of an ultralow expansion(ULE) cavity with a Hertz level resolution. With this approach, the linear and nonlinear drifts of the ULE cavity along a variety of controlled temperatures are clearly presented. When the controlled temperature of ULE cavity is tuned away from the zero-crossing temperature of the ULE cavity, the cavity shows larger and larger nonlinear drift. According to our theoretical analysis and experimental results, we investigate more details of the drift property of the ULE cavity around the zero-crossing temperature, which has seldom been explored before. We can definitely conclude that the zero-crossing temperature of our ULE cavity used in an ytterbium(Yb) lattice clock is around 31.7℃.     

利用传输腔技术实现镱原子光钟光晶格场的频率稳定

为了获得高稳定度和高精确度的原子光晶格钟,光晶格场的频率必须得到锁定,线宽必须控制到特定水平用来消除交流斯塔克频移.本文提出利用传输腔技术来实现对镱原子光钟的光晶格场的频率锁定和抑制频率长期漂移的锁定方案.首先,将一个殷钢材料的传输腔锁定在基于调制转移谱技术锁定的780 nm激光场上,再将759 nm的光晶格光场锁定在传输腔上.实验结果表明,光晶格光场的线宽可以锁定和控制在1 MHz以下.光晶格光场与锁定于氢钟的光梳拍频结果显示,光晶格光场的长期频率稳定度优于3.6×10~(-10),可以确保实现镱原子光钟的不确定度进入10~(-17).