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Chinese Optics Letters

Reaching a few 10-15 long-term stability of integrating sphere cold atom clock

Yaning Wang Yaning Wang, Yan-Ling Meng, Jinyin Wan Jinyin Wan, Ling Xiao, Mingyuan Yu, Xin Wang Xin Wang, Xinchuan Ouyang, Hua-Dong Cheng, Liang Liu Liang Liu

Published Jan 1, 2018• 4 citations
Publisher

Abstract

We present the long-term stability of the integrating sphere cold atom clock (ISCAC) and analyze its systematic limitations. The relative frequency instability of 2.6×10−15 is reached for an averaging time of 2×105  s. The second-order Zeeman effect and the cavity pulling effect in ISCAC, which would induce the frequency drift from the clock transition, are analyzed. The analytical and experimental results indicate that the cavity pulling effect is the main contribution to the long-term frequency instability of the ISCAC. Further technical improvements to the microwave cavity are also discussed.

DOI
10.3788/col201816.070201

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Chinese Physics Letters•Jun 16, 2005•1 citation
We present the long-term stability of the integrating sphere cold
atom clock (ISCAC) and analyze its systematic limitations. The relative
frequency instability of 2.6×10−15 is reached for an averaging
time of 2×105  s. The second-order Zeeman effect and the
cavity pulling effect in ISCAC, which would induce the frequency drift
from the clock transition, are analyzed. The analytical and experimental
results indicate that the cavity pulling effect is the main contribution
to the long-term frequency instability of the ISCAC. Further technical
improvements to the microwave cavity are also discussed.
The medium long-term frequency stability of the integrating sphere cold atom clock was improved. During the clock operation, Rb87 atoms were cooled and manipulated using cooling light diffusely reflected by the inner surface of a microwave cavity in the clock. This light heated the cavity and caused a frequency drift from the resonant frequency of the cavity. Power fluctuations of the cooling light led to atomic density variations in the cavity’s central area, which increased the clock frequency instability through the cavity pulling effect. We overcame these limitations with appropriate solutions. A frequency stability of 3.5×10−15 was achieved when the integrating time τ increased to 2×104 s.
We theoretically and experimentally investigate the Rabi pulling effect in an integrating sphere cold-atom clock (ISCAC). Rabi pulling in an ISCAC is caused by magnetic-sublevel transitions between hyperfine states and is related to the amplitude of the microwave pulse, the bias magnetic field, and the density distribution of cold atoms. Theoretical analysis shows the Rabi closed-loop scheme reduces microwave power fluctuation sensitivity by two orders compared to the Ramsey scheme. Experimentally, the Rabi closed-loop scheme achieves a long-term frequency stability of $1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ at an averaging time of 200000200\phantom{\rule{0.16em}{0ex}}000200000 s.
The influence of laser frequency noise on the stability of a compact cold-atom microwave clock was investigated theoretically in this study. The phase-noisy laser was characterized by a phase-diffusion field. Given the laser linewidth, the analytical expressions of the atomic covariance function and the noise power spectral density of the relative intensity noise transferred from the frequency noise were derived based on stochastic differential equations. Our results provide an effective method to estimate the impact of laser frequency noise on the stability of an integrating sphere cold atomic clock. This method can be extended to other cold atom detection cases.
Abstract Atomic clocks with higher frequency stability and accuracy than traditional space-borne atomic clocks are the cornerstone of long-term autonomous operation of space-time-frequency systems. We proposed a space cold atoms clock based on an intracavity cooling scheme, which captures cold atoms at the center of a microwave cavity and then executes in situ interactions between the cold atoms and microwaves. As a result of the microgravity environment in space, the cold atoms can interact with the microwaves for a longer time, which aids in realizing a high-precision atomic clock in space. This paper presents the overall design, operational characteristics, and reliability test results of the space atomic clock based on the intracavity cooling scheme designed for the operation onboard the China space station. In addition, the engineering prototype performance of the space cold atoms microwave clock is also presented. The ground test results for the clock show a fractional frequency stability of 1.1 × 10−12 τ−1/2 reaching 2.5 × 10−15 at 200,000 s, providing solid technical and data support for its future operation in orbit.
We present an experimental scheme of a cold atom space clock with a movable cavity. By using a single microwave cavity, we find that the clock has a significant advantage, i.e. the longitudinal cavity phase shift is eliminated. A theoretical analysis has been carried out in terms of the relation between the atomic transition probability and the velocity of the moving cavity by taking into account the velocity distribution of cold atoms. The requirements for the microwave power and its stability for atomic π/2 excitation at different moving velocities of the cavity lead to the determination of the proper working parameters of the rubidium clock in frequency accuracy 10 −17 . Finally, the mechanical stability for the scheme is analysed and the ways of solving the possible mechanical instability of the device are proposed.