Research ArticleAPPLIED PHYSICS

Gravity surveys using a mobile atom interferometer

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Science Advances  06 Sep 2019:
Vol. 5, no. 9, eaax0800
DOI: 10.1126/sciadv.aax0800
  • Fig. 1 Atomic gravimeter.

    (A) Schematic. Cesium clouds are loaded in the novel pyramidal MOT and then freely fall into the region of fluorescence detection. k1 and k2 are the wave vectors of the interferometer beams. A magnetic shield and a solenoid (not shown) around the vacuum chamber create a uniform magnetic bias field. The retroreflector consists of a flat mirror and a quarter-wave plate. The vibration isolation stage includes a passive vibration isolation table, a seismometer, voice coils, and an active feedback loop. (B) Mach-Zehnder interferometer geometry. Three laser pulses (wavy green lines) split, redirect, and combine a matter wave (blue and orange lines). (C) Fringes with T = 120 ms and C = 16%. The blue dots are single-shot experimental data, and the red curve is a sinusoidal fit.

  • Fig. 2 Tidal gravity measurement.

    (A) Tidal gravity variation as a function of time. Each blue dot is the mean value of the gravity data over 2 hours. (B) Comparison between the gravity residual and the water level variation in the San Francisco Bay. The gravity residual is the difference between the measurements and the solid Earth tide model. The water level variation is measured by the observatory of National Oceanic and Atmospheric Administration in Richmond, CA. (C) Allan deviation of the residual. The dashed line corresponds to a sensitivity of 37 μGal/Hz. The broad peak around 3 × 104 s is due to the ocean tidal loading. (D) Power spectral density of the residual. The ocean tidal loading results in the peaks around 1 × 10−5 to 3 × 10−5 Hz.

  • Fig. 3 Earthquake seismic waves detected in Berkeley.

    The atomic gravimeter measures the vertical acceleration of the seismic waves with an update rate of 0.13 Hz. The seismic signal is the vertical channel of the seismometer located in Haviland Hall in the University of California (UC) Berkeley campus. It is in arbitrary unit and has an update rate of 0.1 Hz.

  • Fig. 4 Gravity variation on different floors of Campbell Hall.

    The data at 0 m are the gravity measured on the floor of the basement, and the others are from floors 1 to 5. The error bars are 1 − σ statistical and systematic errors. The height of the floors is obtained from the building design. The free-air gradient of −0.3086 mGal/m is removed from the data to emphasize deviations of the VGG from the free-air value. The solid line is a linear fit of the gravity variation measured by the atomic gravimeter from floors 1 to 5 and determines a VGG of −0.289(3) mGal/m. Similarly, the dashed line is a linear fit of the relative gravimeter, determining a VGG of −0.285(1) mGal/m.

  • Fig. 5 Gravity survey in Berkeley Hills.

    (A) Measurement route. The blue curve depicts the route, and the white pin drops are the six measurement locations. (B) Gravity anomaly as a function of the elevation. Elevations are from Google maps. The error bars are 1 − σ statistical and systematic errors. The dashed line indicates a VGG of −0.225(10) mGal/m. (C) The atomic gravimeter apparatus. (D) Field operation of the atomic gravimeter inside a vehicle. [Photo credit for (A): Google Maps; photo credit for (C) and (D): Xuejian Wu, UC Berkeley].

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaax0800/DC1

    Fig. S1. Cesium fluorescence inside the glass vacuum chamber.

    Fig. S2. Measuring absolute gravity with different pulse separation time.

    Fig. S3. Schematic of the laser system.

    Fig. S4. Vibration isolation.

    Fig. S5. Tidal gravity variation.

    Fig. S6. Evaluation of systematic effects.

    Fig. S7. Calibration of alignment to gravity axis.

    Table S1. Systematic effects.

    Table S2. Gravity survey in Campbell Hall in UC Berkeley campus.

    Table S3. Gravity survey in Berkeley Hills.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Cesium fluorescence inside the glass vacuum chamber.
    • Fig. S2. Measuring absolute gravity with different pulse separation time.
    • Fig. S3. Schematic of the laser system.
    • Fig. S4. Vibration isolation.
    • Fig. S5. Tidal gravity variation.
    • Fig. S6. Evaluation of systematic effects.
    • Fig. S7. Calibration of alignment to gravity axis.
    • Table S1. Systematic effects.
    • Table S2. Gravity survey in Campbell Hall in UC Berkeley campus.
    • Table S3. Gravity survey in Berkeley Hills.

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