Sébastien Merlet

The influence of transverse motion within an atomic gravimeter

Limits on the long-term stability and accuracy of a second generation cold atom gravimeter are investigated. We demonstrate a measurement protocol based on four interleaved measurement configurations, which allows rejection of most of the systematic effects, but not those related to Coriolis acceleration and wave-front distortions. Both are related to the transverse motion of the atomic cloud. Carrying out measurements with opposite orientations with respect to the Earths rotation vector direction allows us to separate the effects and correct for the Coriolis shift. Finally, measurements at different atomic temperatures are presented and analyzed. In particular, we show the difficulty of extrapolating these measurements to zero temperature, which is required in order to correct for the bias due to wave-front distortions.

Micro-gravity investigations for the LNE watt balance project

We report on a micro-gravity survey of the laboratories where the LNEs watt balance experiment is being conducted, including the characterization of the Scintrex CG-5 relative gravimeter used for this study. The results of the survey are compared with a model of the gravity field generated by the local mass distribution. The ultimate goal is to transfer an absolute measurement of g from one room to another with minimal uncertainty.

Stability comparison of two absolute gravimeters: optical versus atomic interferometers

We report the direct comparison between the stabilities of two mobile absolute gravimeters of different technology: the LNE-SYRTE Cold Atom Gravimeter and FG5X#216 of the Universite du Luxembourg. These instruments rely on two different principles of operation: atomic and optical interferometry. The comparison took place in the Walferdange Underground Laboratory for Geodynamics in Luxembourg, at the beginning of the last International Comparison of Absolute Gravimeters, ICAG-2013. We analyse a 2h10 duration common measurement, and find that the CAG shows better immunity with respect to changes in the level of vibration noise, as well as a slightly better short term stability.

The European Comparison of Absolute Gravimeters 2011 (ECAG-2011) in Walferdange, Luxembourg: results and recommendations

We present the results of the third European Comparison of Absolute Gravimeters held in Walferdange, Grand Duchy of Luxembourg, in November 2011. Twenty-two gravimeters from both metrological and non-metrological institutes are compared. For the first time, corrections for the laser beam diffraction and the self-attraction of the gravimeters are implemented. The gravity observations are also corrected for geophysical gravity changes that occurred during the comparison using the observations of a superconducting gravimeter. We show that these corrections improve the degree of equivalence between the gravimeters. We present the results for two different combinations of data. In the first one, we use only the observations from the metrological institutes. In the second solution, we include all the data from both metrological and non-metrological institutes. Those solutions are then compared with the official result of the comparison published previously and based on the observations of the metrological institutes and the gravity differences at the different sites as measured by non-metrological institutes. Overall, the absolute gravity meters agree with one another with a standard deviation of 3.1 µGal. Finally, the results of this comparison are linked to previous ones. We conclude with some important recommendations for future comparisons.

Operating an atom interferometer beyond its linear range

In this paper, we show that an atom interferometer inertial sensor, when associated with the auxiliary measurement of external vibrations, can be operated beyond its linear range and still keep a high acceleration sensitivity. We propose and compare two measurement procedures (fringe fitting and non-linear lock) that can be used to extract, without adding any bias, the mean phase of the interferometer when the interferometer phase fluctuations exceed 2?. Despite operating in the urban environment of inner Paris without any vibration isolation, the use of a low noise seismometer for the measurement of ground vibrations allows our atom gravimeter to reach at night a sensitivity as good as 5.5 ? 10?8g at 1?s. Robustness of the measurement to large vibration noise is also demonstrated by the ability of our gravimeter to operate during an earthquake with excellent sensitivity. For such low vibration frequency though, high pass filtering of the seismometer degrades its correlation with the interferometer signal, so that low frequency seismic vibrations appear on the gravity measurement. Nevertheless, our high repetition rate allows for efficient sampling of these perturbations, ensuring proper averaging. Such techniques open new perspectives for applications in other fields, such as navigation and geophysics.

Relative Gravity Measurement Campaign during the 7th International Comparison of Absolute Gravimeters (2005)

Since the 1st International Comparison of Absolute Gravimeters (ICAG) and accompanying Relative Gravity Campaign (RGC) held at the BIPM in 1981, repeated ICAG-RGCs have been organized every four years. A total of 19 absolute gravimeters (AG) and 15 relative gravimeters (RG) participated in the 7th ICAG-RGC, which took place in 2005. Co-located absolute and relative gravity measurements as well as precision levelling measurements were carried out. The final version of the absolute g values of the 7th ICAG has been officially released recently. This paper is the final report of the 7th RGC and replaces the preliminary results published earlier. It covers the organization of the RGC and the data processing, analyses RG behaviour, computes g, δg and OAG (offset of AG) and discusses their uncertainties. In preparation for the BIPM key comparison ICAG-2009, a standard data-processing procedure has been developed and installed in the BIPM ICAG-RGC software package, GraviSoft. This was used for the final data processing.

First determination of the Planck constant using the LNE watt balance

After separate developments of the different elements with continuous characterizations and improvements, the LNE watt balance has been assembled. This paper describes the system in detail and gives its first measurements of the Plancks constant h. The value determined in air is h = 6.626 068 8(20) × 10−34 Js which differs in relative terms by −0.05 × 10−7 from the h90 value and by −1.1 × 10−7 from that of the 2010 CODATA adjustment of h. The relative standard uncertainty associated is 3.1 × 10−7.

Hybridizing matter-wave and classical accelerometers

We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performances without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely the dead times between consecutive measurements.

Perturbations of the local gravity field due to mass distribution on precise measuring instruments: a numerical method applied to a cold atom gravimeter

We present a numerical method, based on a FEM simulation, for the determination of the gravitational field generated by massive objects, whatever geometry and space mass density they have. The method was applied for the determination of the self-gravity effect of an absolute cold atom gravimeter which aims at a relative uncertainty of 10−9. The deduced bias, calculated with a perturbative treatment, is finally presented. The perturbation reaches (1.3 ± 0.1) × 10−9 of the Earths gravitational field.

Underground operation at best sensitivity of the mobile LNE-SYRTE cold atom gravimeter

Low noise underground environments offer conditions allowing assessment of ultimate performance of high sensitivity sensors such as accelerometers, gyrometers, seismometers⋯ Such facilities are for instance ideal for observing the tiny signals of interest for geophysical studies. Laboratoire Souterrain à Bas Bruit (LSBB) in which we have installed our cold atom gravimeter provides such an environment. We report here the best short term sensitivity ever obtained without any ground vibration isolation system with such an instrument: 10−8 m s−2 in 100 s measurement time.