arXiv subjects

F. Pereira Dos Santos

Publications and source records attributed to F. Pereira Dos Santos.

At least 19 recordsLinked to original sources

arXiv2022

CARIOQA: Definition of a Quantum Pathfinder Mission

A strong potential gain for space applications is expected from the anticipated performances of inertial sensors based on cold atom interferometry (CAI) that measure the acceleration of freely falling independent atoms by manipulating them with laser light. In this context, CNES and its partners initiated a phase 0 study, called CARIOQA, in order to develop a Quantum Pathfinder Mission unlocking key features of atom interferometry for space and paving the way for future ambitious space missions utilizing this technology. As a cornerstone for the implementation of quantum sensors in space, the CARIOQA phase 0 aimed at defining the Quantum Pathfinder Mission's scenario and associated performance objectives. To comply with these objectives, the payload architecture has been designed to achieve long interrogation time and active rotation compensation on a BEC-based atom interferometer. A study of the satellite architecture, including all the subsystems, has been conducted. Several technical solutions for propulsion and attitude control have been investigated in order to guarantee optimal operating conditions (limitation of micro-vibrations, maximization of measurement time). A preliminary design of the satellite platform was performed.

physics.atom-ph↗

arXiv2021

Calibration of a superconducting gravimeter with an absolute atom gravimeter

We present a 27-days long common view measurement of an absolute cold atom gravimeter (CAG) and a relative iGrav superconducting gravimeter, which we use to calibrate the iGrav scale factor. This allowed us to push the CAG long-term stability down to the level of 0.5~nm.s$^{-2}$. We investigate the impact of the duration of the measurement on the uncertainty in the determination of the correlation factor and show that it is limited to about 3\textperthousand~by the coloured noise of our cold atom gravimeter. A 3-days long measurement session with an additional FG5X absolute gravimeter allows us to directly compare the calibration results obtained with two different absolute meters. Based on our analysis, we expect that with an improvement of its long term stability, the CAG will allow to calibrate the iGrav scale factor to better than the per mille level (1$σ$ level of confidence) after only one-day of concurrent measurements for maximum tidal amplitudes.

physics.ins-det↗

arXiv2020

Gravity Field Mapping Using Laser Coupled Quantum Accelerometers in Space

The emergence of quantum technologies, including cold atom based accelerometers, offers an opportunity to improve the performances of space geodesy missions. In this context, CNES initiated an assessment study called GRICE (GRadiométrie à Interféromètres quantiques Corrélés pour l'Espace) in order to evaluate the contribution of cold atom technologies to space geodesy and to the end users of geodetic data. In this paper, we present mission scenario for gravity field mapping based on a long baseline gradiometer. The mission is based on a constellation of two satellites, flying at an altitude of 373 km, each equipped with a cold atom accelerometer with a sensitivity of $6 \times 10^{-10}$~m.s$^{-2}$.$\mathrmτ^{-1/2}$. A laser link measures the distance between the two satellites and couples these two instruments in order to produce a correlated differential acceleration measurement. The main parameters, determining the performances of the payload, have been investigated. We carried out a general study of satellite architecture and simulations of the mission performances in terms of restitution of the gravity field. The simulations show that this concept would give its best performance in terms of monthly gravity fields recovery under 1000~km resolution. In the resolution band between 1000 and 222~km, the improvement of the GRICE gradient approach over the traditional range-rate approach is globally in the order of 10 to 25\%.

physics.atom-ph↗

arXiv2015

Influence of chirping the Raman lasers in an atom gravimeter: phase shifts due to the Raman light shift and to the finite speed of light

We present here an analysis of the influence of the frequency dependence of the Raman laser light shifts on the phase of a Raman-type atom gravimeter. Frequency chirps are applied to the Raman lasers in order to compensate gravity and ensure the resonance of the Raman pulses during the interferometer. We show that the change in the Raman light shift when this chirp is applied only to one of the two Raman lasers is enough to bias the gravity measurement by a fraction of $μ$Gal ($1~μ$Gal~=~$10^{-8}$~m/s$^2$). We also show that this effect is not compensated when averaging over the two directions of the Raman wavevector $k$. This thus constitutes a limit to the rejection efficiency of the $k$-reversal technique. Our analysis allows us to separate this effect from the effect of the finite speed of light, which we find in perfect agreement with expected values. This study highlights the benefit of chirping symmetrically the two Raman lasers.

physics.atom-ph↗

arXiv2011

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 \pm 0.1) \times 10-9 of the Earth's gravitational field.

physics.atom-ph↗

arXiv2010

Comparison of 3 absolute gravimeters based on different methods for the e-MASS project

We report on the comparison between three absolute gravimeters that took place in April 2010 at Laboratoire National de Métrologie et d'Essais. The three instruments (FG5#209 from METAS, Switzerland, IMGC-02 from INRIM, Italy, and CAG from LNE-SYRTE, France) rely on different methods: optical and atomic interferometry. We discuss their differences as well as their similarities. We compare their measurements of the gravitational acceleration in 4 points of the same pillar, in the perspective of an absolute determination of g for a watt balance experiment

physics.atom-ph↗

arXiv2010

Comparison between two mobile absolute gravimeters: optical versus atomic interferometers

We report a comparison between two absolute gravimeters: the LNE-SYRTE cold atoms gravimeter and FG5#220 of Leibniz Universität of Hannover. They rely on different principles of operation: atomic and optical interferometry. Both are movable which enabled them to participated to the last International Comparison of Absolute Gravimeters (ICAG'09) at BIPM. Immediately after, their bilateral comparison took place in the LNE watt balance laboratory and showed an agreement of 4.3 +/- 6.4 μGal.

physics.atom-ph↗

arXiv2008

Wide bandwidth phase-locked diode laser with an intra-cavity electro-optic modulator

Two extended cavity laser diodes are phase-locked, thanks to an intra-cavity electro-optical modulator. The phase-locked loop bandwidth is on the order of 10 MHz, which is about twice larger than when the feedback correction is applied on the laser current. The phase noise reaches -120 dBrad$^2$/Hz at 10 kHz. This new scheme reduces the residual laser phase noise, which constitutes one of the dominant contributions in the sensitivity limit of atom interferometers using two-photon transitions.

physics.optics↗

arXiv2007

Influence of lasers propagation delay on the sensitivity of atom interferometers

In atom interferometers based on two photon transitions, the delay induced by the difference of the laser beams paths makes the interferometer sensitive to the fluctuations of the frequency of the lasers. We first study, in the general case, how the laser frequency noise affects the performance of the interferometer measurement. Our calculations are compared with the measurements performed on our cold atom gravimeter based on stimulated Raman transitions. We finally extend this study to the case of cold atom gradiometers.

physics.atom-ph↗

arXiv2006

First observation of feshbach resonances at very low magnetic field in a 133Cs fountain

One of the main limitations of cesium atomic fountains has been the cold collision frequency shift. By using a method based on a transfer of population by adiabatic passage allowing to prepare cold atomic samples with a well defined ratio of atomic density as well as atom number the collisional shift is controlled at the 10E-3 of its value. A calibration of Zeeman sub-states contribution to the clock shift as a function of the field has been performed. Feshbach resonances have been observed for the first time at very low magnetic field and with a very good resolution. A Monte Carlo simulation has been performed and could fit properly some of experimental data. This constrains some parameters of the theory of collisions.

physics.atom-ph↗

arXiv2005

Transportable laser system for atom interferometry

We describe an optical bench in which we lock the relative frequencies or phases of a set of three lasers in order to use them in a cold atoms interferometry experiment. As a new feature, the same two lasers serve alternately to cool atoms and to realize the atomic interferometer. This requires a fast change of the optical frequencies over a few GHz. The number of required independent laser sources is then only 3, which enables the construction of the whole laser system on a single transportable optical bench. Recent results obtained with this optical setup are also presented.

physics.atom-ph↗

arXiv2005

Measurement of the sensitivity function in time-domain atomic interferometer

We present here an analysis of the sensitivity of a time-domain atomic interferometer to the phase noise of the lasers used to manipulate the atomic wave-packets. The sensitivity function is calculated in the case of a three pulse Mach-Zehnder interferometer, which is the configuration of the two inertial sensors we are building at BNM-SYRTE. We successfully compare this calculation to experimental measurements. The sensitivity of the interferometer is limited by the phase noise of the lasers, as well as by residual vibrations. We evaluate the performance that could be obtained with state of the art quartz oscillators, as well as the impact of the residual phase noise of the phase-lock loop. Requirements on the level of vibrations is derived from the same formalism.

physics.atom-ph↗

arXiv2004

New Limits to the Drift of Fundamental Constants from Laboratory Measurements

We have remeasured the absolute $1S$-$2S$ transition frequency $ν_{\rm {H}}$ in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of $(-29\pm 57)$ Hz for the drift of $ν_{\rm {H}}$ with respect to the ground state hyperfine splitting $ν_{\rm {Cs}}$ in $^{133}$Cs. Combining this result with the recently published optical transition frequency in $^{199}$Hg$^+$ against $ν_{\rm {Cs}}$ and a microwave $^{87}$Rb and $^{133}$Cs clock comparison, we deduce separate limits on $\dotα/α= (-0.9\pm 2.9)\times 10^{-15}$ yr$^{-1}$ and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments $μ_{\rm {Rb}}/μ_{\rm {Cs}}$ equal to $(-0.5 \pm 1.7)\times 10^{-15}$ yr$^{-1}$. The latter provides information on the temporal behavior of the constant of strong interaction.

physics.optics↗

arXiv2003

Astrophysical constraints on hypothetical variability of fundamental constants

(Abridged) Many-multiplet (MM) method applied to three inhomogeneous samples of Keck/HIRES quasar absorption spectra gives a shift in the value of the fine-structure constant of Delta alpha/alpha = (-5.4+/-1.2) 10^{-6} in the redshift range 0.2 < z < 3.7 (Murphy et al. 2003).The 1sigma error is, however, much too small and cannot be maintained by current observations of quasars. We present a modified MM method to set an upper limit on Delta alpha/alpha from a homogeneous sample of FeII lines identified in the up-to-date best quality VLT/UVES spectrum of HE 0515-4414. Our result is Delta alpha/alpha = (1.1+/-1.1) 10^{-5} at z = 1.149. Theoretical models of the fundamental physical interactions predict that the proton-to-electron mass ratio (mu = m_p/m_e) may relate to the shift in Delta alpha/alpha as Delta mu/mu = R Delta alpha/alpha. We use VLT/UVES high-resolution observations of molecular hydrogen H2 ultraviolet absorption lines at z = 3.025 toward Q 0347-3818 to bound the value of R. The obtained constraints on Delta ln mu = (2.1+/-3.6) 10^{-5} and on Delta ln alpha = (1.1+/-1.1) 10^{-5} rule out vary large values of |R| > 6.

astro-ph↗

arXiv2002

A Search for Variations of Fundamental Constants using Atomic Fountain Clocks

Over five years we have compared the hyperfine frequencies of 133Cs and 87Rb atoms in their electronic ground state using several laser cooled 133Cs and 87Rb atomic fountains with an accuracy of ~10^{-15}. These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies : (d/dt)ln(nu_Rb/nu_Cs)=(0.2 +/- 7.0)*10^{-16} yr^{-1} (1 sigma uncertainty). The same limit applies to a possible variation of the quantity (mu_Rb/mu_Cs)*alpha^{-0.44}, which involves the ratio of nuclear magnetic moments and the fine structure constant.

physics.atom-ph↗

arXiv2002

Controlling the cold collision shift in high precision atomic interferometry

We present here a new method based on a transfer of population by adiabatic passage that allows to prepare cold atomic samples with a well defined ratio of atomic density and atom number. This method is used to perform a measurement of the cold collision frequency shift in a laser cooled cesium clock at the percent level, which makes the evaluation of the cesium fountains accuracy at the $10^{-16}$ level realistic. With an improved set-up, the adiabatic passage would allow measurements of atom number-dependent phase shifts at the $10^{-3}$ level in high precision experiments.

physics.atom-ph↗

arXiv2001

Bose-Einstein Condensation of Metastable Helium

We have observed a Bose-Einstein Condensate in a dilute gas of $^4$He in the $2^3S_1$ metastable state. We find a critical temperature of $(4.7\pm0.5) μ$K and a typical number of atoms at the threshold of $8\times10^6$. The maximum number of atoms in our condensate is about $5\times10^5$. An approximate value for the scattering length $a=(16\pm8)$ nm is measured. The elastic collision rate is then estimated to be about $5\times10^4$ s$^{-1}$, indicating that we are deeply in the hydrodynamic regime. The typical decay time of the condensate is 2 s which places an upper bound on the rate constants for 2-body and 3-body inelastic collisions.

cond-mat↗

arXiv2001

Penning collisions of laser-cooled metastable helium atoms

We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient $β$ on the excited state ($2^3P_2$) and metastable state ($2^3S_1$) populations is also investigated. From these results we infer a rather uniform rate constant $K_{sp}=(1{\pm}0.4)\times10^{-7}$ cm$^3$/s.

physics.atom-ph↗