Realization of Closed-Loop Operation of Optical Lattice Clock Based on 171Yb

We report the realization of closed-loop operation of an optical lattice clock based on 171Yb atoms. We interrogate the 1So →3p0 clock transition using single Rabi pulses of 578nm laser light. The two It-transitions from mE = 4-1/2 ground states are alternatively interrogated, and the clock laser frequency is locked to the center of the two resonances. The in-loop error signal stability of the clock reaches 3 × 10-17 for an average time of 3500s. We also perform interleaved operations of the clock with two independent servo loops, and the fractional frequency difference averages down to 2 × 10-16 in 7200s.

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℃.

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 6.5μK to less than 0.8μK in the trap depth of 24μK,corresponding to an average axial motional quantum number<nz><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.