Absolute Quantum Gravimeter
The Muquans Absolute Quantum Gravimeter is the first commercial gravimeter based on laser-cooled atoms. After 15 years of research, this technology has proven its capability to perform absolute gravity measurements at the microGal level over long periods of time.
• Compact and transportable sensor.
• Significantly low maintenance constraints (in particular, no moving parts in our vacuum chamber).
• Ease and quickness of Operation : the AQG is ready to measure within 1h (no laser alignment nor mechanical assembling,
no preliminary pumping, no superspring). User-friendly software requiring no knowledge in quantum physics.
• Absolute gravity measurement at the µGal level at a few Hz cycling frequency.
• Excellent immunity to ground vibrations thanks to an active compensation system (no mechanical isolation).
• Automated Continuous Data Acquisition for several months. No observed long-term drift.
• Station to station reproducibility of the absolute measurement within a few μGal.
With a single unit of the AQG one can now perform:
- station based long-term monitoring of g in presence of seismic noise
- local absolute determination of g and easy change of location
- gravity mapping without redundant loops and high-precision transfers of g (indoor mapping, gravity gradients …).
With the AQG, a station can be measured at the microGal level within 1h30 (set-up and calibration of the sensor included).
Principle of operation
The AQG relies on the same basic principle as absolute free fall gravimeters. However, instead of using a falling mirror, the gravity measurement is performed with falling laser-cooled atoms. This technique is one of the ballistic freefall method proclaimed by the BIPM (Bureau International des Poids et Mesures) as an official primary method for the measurement of gravity.
A typical measurement sequence is organized as follows:
• First, atoms are trapped in the vacuum chamber with lasers and cooled down to a temperature of a few µK.
• All laser beams are shut down so that the cold atoms experience a free-fall.
• The vertical acceleration experienced by the atoms during a 10 cm fall is precisely characterized with an advanced interferometric scheme relying on lasers.
This technique provides a very accurate gravity measurement method, which gives a direct access to the absolute value of the gravity. The AQG is therefore inherently calibrated and does not experience any measurable drift over time.
In addition, utilization of atom cooling and trapping techniques allows a fast measurement cycle, with a repetition frequency up to
5 Hz, and does not require any moving parts in the vacuum chamber, which leads to a very high reliability.
Here are the specification of our AQG:
|Sensitivity||50 µGal/√Hz (demonstrated)|
|Measurement frequency||2 Hz|
|Long-term stability||~ 1 μGal|
|Accuracy||A few μGal (under evaluation)|
The characteristics of the physics package of the AQG are:
|Dimensions||Sensor head: h = 70 cm / D = 38 cm
Laser & electronics: 100 x 50 x 70 cm3
|Mass||100 kg (without flight cases)|
|Power consumption||300 W typical|
A hybridized version of our AQG is also available. It allows to obtain an acceleration signal which is:
• Very large band [DC ; 430 Hz], and ultra-sensitive
• Accurate and ultra-stable on the long-term.
The AQG then provides both the value of g and the seismic signal simultaneously. This is especially intended to support seismic and tectonic surveys.
Implementation is inertial navigation is also envisioned.