No abstract

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 × 10 −8 g/Hz 1/2 . We measured the local gravitational acceleration g by this sensitive gravimeter with a resolution of 6.5 × 10 −9 g after 60 s and 1.5 × 10 −9 g after 2000 s integration time, which is comparable to the resolution of state-of-the-art atom gravimeters.

The magnetic field gradient has been measured with an atom interferometer using the magnetic sublevels of 87 Rb atoms. The Doppler-insensitive measurement effectively eliminates the contribution from gravity and background vibration noise, and the differential measurement also can reject some systematic errors. A resolution of 300 pT/mm has been demonstrated with a 90-s integration time and a spatial resolution of 1.4 mm. The gradiometer was then used to measure the magnetic field gradient in an ultrahigh-vacuum environment. The technique will also be very useful to subtract the systematic error arising from the magnetic field inhomogeneity in precision atom-interferometry experiments, such as gravity measurement.

Precisely measuring the magnetic-field gradient within a vacuum chamber is important for many precision experiments and can be realized by atom interferometry using magnetically sensitive sublevels at different times to make a differential measurement, which had been demonstrated in our previous work. In this paper, we demonstrate a differential method to measure the magnetic-field gradient by means of two simultaneously operated atom interferometers using double atomic fountains. By virtue of this simultaneous differential measurement to reject common-mode noise, the resolution can be improved by one order of magnitude for about a 1000-s integration time.

Precisely determining gravity acceleration g plays an important role on both geophysics and metrology. For gravity measurements and high-precision gravitation experiments, a cold atom gravimeter with the aimed resolution of 10 −9 g/Hz 1/2 (1 g=9.8 m/s 2 ) is being built in our cave laboratory. There will be four steps for our 87 Rb atom gravimeter, Magneto-Optical Trap (MOT) for cooling and trapping atoms, initial state preparation, π/2-π-π/2 Raman laser pulse interactions with cold atoms, and the final state detection for phase measurement. About 10 8 atoms have been trapped by our MOT and further cooled by moving molasses, and an atomic fountain has also been observed.