3 December 2023
Development of a laboratory setup for gradiometry
The gradiometer being developed at SYRTE will combine 1) ultracold atomic sources prepared on atom chips and 2) the use of large momentum beamsplitters. These two key elements will be combined to realize interferometers based on beamsplitters of several tens or hundreds of ħk in a fountain geometry. For an interferometer duration of 2T = 500 ms, a separation of 100 ħk, a cycle time of 2 s and a number of atoms of 105 per source, the differential accelerometric sensitivity will be of 1.3 10-11g at 1 s. For a distance between sources of one meter, the sensitivity on the gravity gradient will be of 126 mE at 1 s.
Differential phase extraction
We have recently demonstrated a new method for the extraction of the differential phase [M. Langlois et al., Phys. Rev. A 96, 053624 (2017)], which exploits correlations between the phases of the two interferometers and an estimation of the seismic phase, determined thanks to the simultaneous measurements of ground vibrations with a seismometer. This method, which we had proposed a few years ago [F. Pereira Dos Santos, Phys. Rev. A 91, 063615 (2015)], allows to reject vibration noise with an efficiency limited by the detection noise, and allows retrieving the differential phase without bias, by contrast with the methods used so far.
Simultaneous accurate determination of g and its vertical gradient
We have recently implemented a method for the accurate measurements of both the gravity g and its vertical gradient. Two atomic samples are prepared at different heights and released. During their free fall, two simultaneous interferometers are performed with the same Raman beam. Using a frequency chirp and a frequency jump on this Raman beam frequency, we realize a dual lock which stirs simustaneously the chirp to compensate for g and the jump to compensate for the vertical gravity gradient. We then determine these two quantities in terms of frequencies. Moreover, this technique does not require the precise knowledge of the « gradiometer baseline », i.e. the distance between the two sources, which is difficult to determine precisely. The following figure displays the evolution of g and its gradient obtained with the implemented dual lock method. One clearly sees the rejection of the common mode vibration noise in the gradient measurement.
- Results of the dual lock measurement.
- Top: Gravity acceleration measurement fluctuation. Bottom: Gravity gradient measurement fluctuation.
This measurement method is used in the industrial gradiometer prototype developed by iXblue, to which we contributed in the frame of collaborative projects funded by DGA and then ANR.
Bragg interferometers
We have implemented light beamsplitters based on Bragg transitions and realized a dual interferometer, with atoms launched upwards, with a maximum duration of 500 ms. We have implemented a new method of separating the output ports of the interferometer, based on the selective acceleration of one of the output ports using an accelerated lattice. A preliminary sensitivity of about 200 E at 1s has been demonstrated.
- Time of flights
- a) with no Bragg pulse nor separator b) with a Bragg pulse but no separator c) with a Bragg pulse and a separator
Status of the project
We have installed in the top trap zone a first generation atom chip, which will be used for the production of ultracold atoms. An independent test chamber has also been developed to test second generation chips. Next steps will be the validation of this key-subsystem and the implementation of large momentum transfer beamsplitters.
Publications
Raphaël Piccon, Sumit Sarkar, Sébastien Merlet, Franck Pereira dos Santos
"Separating the output ports of a Bragg interferometer via velocity selective transport"
Phys. Rev. A 106, 013303 (2022)
Sumit Sarkar, Raphael Piccon, Sebastien Merlet, and Franck Pereira dos Santos
"A simple and robust architecture of laser system for atom interferometry"
Optics Express Vol. 30, Issue 3, pp. 3358-3366 (2022)
Camille Janvier, Vincent Ménoret, Sébastien Merlet, Arnaud Landragin, Franck Pereira Dos Santos, Bruno Desruelle
"A compact differential gravimeter at the quantum projection noise limit"
Phys. Rev. A 105, 022801 (2022).
Copyright 2022 by the American Physical Society
R. Caldani, S. Merlet, F. Pereira dos Santos, G. Stern, A.-S. Martin, B. Desruelle, V. Ménoret
"A prototype industrial laser system for cold atom inertial sensing in space"
Eur. Phys. J. D 73, 248 (2019)
R. Caldani, K. Weng, S. Merlet, Franck Pereira dos Santos
“Simultaneous accurate determination of both gravity and its vertical gradient”
Phys. Rev. A 99, 033601 (2019)
M. Langlois, R. Caldani, A. Trimeche, S. Merlet, and F. Pereira Dos Santos
“Differential phase extraction in dual interferometers exploiting the correlation between classical and quantum sensors”
Phys. Rev. A 96, 053624 (2017)
Copyright 2017 by the American Physical Society
F. Pereira Dos Santos
“Differential phase extraction in an atom gradiometer”
Phys. Rev. A 91, 063615 (2015)
Copyright 2015 by the American Physical Society