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Quantum gravimeters

Ultra-precision gravity measurement



Thanks to the advances of quantum technologies, Exail is able to provide a turn-key transportable quantum sensor measuring gravity at a level of 10-8 m/s2.

The Absolute Quantum Gravimeter (AQG) measures the acceleration of a free-falling test mass in vacuum: the ballistic free-fall of an ensemble of laser-cooled atoms is accurately monitored, and the acceleration of gravity is then inferred. This technique is one of the ballistic free-fall methods proclaimed by the BIPM (Bureau International des Poids et Mesures) as an official primary method for the measurement of gravity.

Features

Benefits

    • Absolute gravity measurement at a level of 10-8 m/s2 (1 μGal) in terms of sensitivity, stability and repeatability
    • Continuous data acquisition from a few seconds to several years
    • Transportable device allowing to perform surveys, time-lapse measurement of a network of reference stations or stationary measurements with the same instrument

Applications

  • Geophysics (reservoir monitoring and geodesy)
  • Civil engineering (sub-surface imaging)
  • Metrology

A free-fall absolute gravimeter using quantum technologies and laser-cooled atoms

The Absolute Quantum Gravimeter (AQG) is today the only commercial industry-grade gravity meter to enable continuous absolute measurements from a few seconds to several years. Being at the same time easily transportable it can be deployed anywhere on the planet both indoor and outdoor. This makes the AQG highly suitable for a wide range of applications in geophysics, metrology and civil engineering.

For high-precision gravity measurements

The AQG exploits the principle of atom interferometry with laser-cooled atoms. This unique solution is the result of more than 15 years of research conducted by our academic partners (LP2N and LNE-SYRTE). The AQG comes in 2 versions: the AQG-A for indoor use and the AQG-B for field measurements.

The AQG comes in 2 versions: the AQG-A for indoor use and the AQG-B for field measurements.

Exail quantum gravimetry etna

A turn-key transportable and easy-to-operate quantum sensor

  • Installation time: 20 minutes (no optical alignment, no mechanical assembly, no pumping required prior to measuring)
  • Maintenance: Low maintenance effort (no moving parts, no gasket nor belt to replace)
  • Robustness to ground vibration: Sub-μGal resolution even in urban environments (without any spring-based mechanical isolation device)
  • Autonomy: Transport and storage for several weeks without any power supply will not affect measurement capability nor require additional pumping (sealed dropping chamber)
  • Software: Dedicated and user-friendly data acquisition and system controller software.
    • Automated starting procedure
    • Automated self-calibration procedures
    • Remote monitoring and real-time data retrieval
  • Data processing: Gravity data is real-time processed with corrections from local tides, atmospheric pressure, tilt variations, ocean loading and polar motion
  • Auxiliary sensors: The sensor head of the AQG houses a classical 3D accelerometer, a pressure gauge, tiltmeters, temperature sensors.

Providing high-quality gravity data

  • Data from V. Ménoret, et al., Gravity measurements below 10−9 g with a transportable absolute quantum gravimeter, Nature Scientific Report, 8:12300 (2018)

The AQG is a flexible gravity sensor able to perform: surveys reaching a resolution of a few µGal with short integration time (Fig. 1), reference station and time-lapse measurements at 1 µGal (Fig. 2) and drift-free long-term continuous gravity monitoring with ultra-high sensitivity (Fig. 3).

    These values of g are corrected from local tides, atmospheric pressure, tilt deviations and ocean loading. In Fig. 2, error bars correspond to the value of the Allan Deviation of the entire data-set calculated at one hour integration time, which corresponds to the statistical uncertainty of this measurement.

    This uninterrupted time series has lasted one month and shows local tides. When data are averaged over long durations, the AQG provides drift-free sub-μGal stability.


Simple and compact quantum gravimeter

The design of the AQG relies on a patented opto-mechanical architecture using a pyramidal retro-reflector. This configuration allows to perform the measurement sequence with a single laser beam instead of up to eight usually, leading to a drastic simplification of the instrument.

High-reliability fibered optical components

The laser system developed by Exail relies on the use of lasers operating at 1560 nm. This approach therefore gives access to a wide variety of high performance fibered optical components, originally developed for high-bit-rate optical communication systems. Thanks to the technological efforts conducted over the last 20 years by the telecom industry, these components present unique features:

  • Fibered components: no optical alignment required
  • Remarkable optical and electrical performances
  • Compliance with Telcordia qualification procedures (extended temperature range)
  • High reliability (lifetime > 50 000 h).

High immunity to ground vibrations

The AQG efficiently rejects ground vibration noise with an active compensation technique that does not require any mechanical isolation device or superspring.

Specifications of the AQG-A and AQG-B

Performance

Exail product absolute quantum gravimeter aqg a full web

AQG-A (indoor)

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AQG-B (field)

Typical Precision at quiet site

500 nm/s²/sqrt(t) 1
50 nm/s² in 1,5 min
20 nm/s² in 10 min
10 nm/s² in 40 min

500 nm/s²/sqrt(t)1, 2
50 nm/s² in 1,5 min
20 nm/s² in 10 min
10 nm/s² in 40 min

Long-term stability

≤ 20 nm/s²

≤ 20 nm/s²

Trueness

≤ 150 nm/s² 3

≤ 150 nm/s² 3

Repeatability

≤ 50 nm/s²

≤ 50 nm/s²

Cycling frequency

>1 Hz

>1 Hz

Physics package

Number of boxes / Maximum mass
of each box / Total mass

3 / 45 Kg / < 100 Kg

5 / 40 kg /< 140 kg

Dimensions of sensor head

1 module: Ø= 40 cm / H= 100 cm / (tripod incl.)

1 module: Ø= 40 cm / H=100 cm / (tripod incl.)

Dimensions of control unit

1 module: H = 70 cm x W = 55 cm x L = 70 cm

2 modules: h = 41 cm x w = 59 cm x l = 105 cm

Length of the cable between
sensor head and laser system

15 m

15 m

Warm up time (typical) /
Start & stop function

2 h

2 h

System Interface & Control

Control system

External computer (Linux OS)

External computer (Linux OS)

User Interface

Dedicated software and set-up tool

Dedicated software and set-up tool

Remote Control and Monitoring

With TeamViewer

With TeamViewer

Data format

.csv (All corrections (tides, ocean loading, atmospheric pressure) are recorded for easy post-processing

.csv (All corrections (tides, ocean loading, atmospheric pressure) are recorded for easy post-processing

Environmental & Physical Specifications

Operating Temperature / Storage temperature

[18-24] °C / [5-30] °C

[0 ; 40] °C / [5 ; 30] °C

Humidity

60%

60%

AC DC Power requirements

Operating Voltage

110 V/230 V

110 V/230 V

Voltage level

350 W

12V or 24 V

Operating power consumption


500 W

Publications