Performance of a cold-atom gravimeter with an active vibration isolator

A cold rubidium atom fountain interferometry gravimeter with an active vibration isolator is demonstrated. The natural resonance frequency of the active vibration isolator is 0.016 Hz, and the vertical vibration noise is greatly reduced by a factor of 100 from 0.1 to 1 Hz. After substantial suppression of the vibration noise, the gravimeter reaches a sensitivity of ${5.5\times 10}^{-8}$ g/Hz${}^{1/2}$. We measured the local gravitational acceleration $g$ by this sensitive gravimeter with a resolution of ${6.5\times 10}^{-9}$ g after 60 s and ${1.5\times 10}^{-9}$ g after 2000 s integration time, which is comparable to the resolution of state-of-the-art atom gravimeters.

Figure 1

Experimental setup of the atom gravimeter based on an active vibration isolator. The inset describes the $D_2$ line energy-level scheme of ${}^{87}$Rb and the frequency components of the Raman beams. The dimensions of the vacuum chamber and the active isolator are about $1.6\times 0.5\times 0.5$ m${}^3$ and $0.4\times 0.4\times 0.5$ m${}^3$, respectively. HPF: high-pass filter, PC: phase compensators, VCCS: voltage-controlled current source.

Figure 2

(a) Vertical vibration noise deduced from the acceleration error signal. (b) Step response of the active vibration isolator.

Figure 3

(a) Atom interference fringe for Raman pulse spacing $T=200$ ms obtained without averaging in 60 s. (b) Tide data recorded by the atom gravimeter between 28 and 31 October 2011. There are some breaks due to laser mode hopping in the first 16 h; after that, this gravimeter worked continuously for several days.

Figure 4

Allen deviation of gravity measurements corrected from the earth's tides.