Travaux en gravimétrie au SYRTE

Transcription

1 Travaux en gravimétrie au SYRTE F. Pereira Dos Santos LNE-SYRTE (OP, LNE, UPMC, CNRS) CNFGG, 1er Février

2 Outline 1. Principle of Atom Interferometry 2. Cold Atom Gravimeters 3. Cold Atom Interferometer Gravity Gradiometry 2

3 Outline 1. Principle of Atom Interferometry 2. Cold Atom Gravimeters 3. Cold Atom Interferometer Gravity Gradiometry 3

4 Principle of atom interferometry Analogy with optical interferometry Use atom-laser interaction to deflect matter waves 4

5 Stimulated Raman transitions Three level atom Interacting with two counter propagating lasers Momentum M transfer Phase difference between the lasers gets imprinted 5

6 Rabi oscillations Rabi oscillation between f> and e> π pulse = mirror Transition Probability f e 1 1/2 π/2 pulse = beam splitter Pulse duration

7 Phase difference between the two paths p/2 p p/2 up down (0) 2 (T) (2 T) (t) k z(t) eff For a constant acceleration a Sampling of the positions at the three pulses Sa Scale factor scales as T 2 => Benefit of cold atoms 7

8 Measurement of the phase difference p/2 p p/2 Normalized detection of the two populations by fluorescence P = N up /(N up +N down ) DDS1 (Hz) Signal at the output of the interferometer Probabilité de transition (MHz.s -1 ) 8

9 Typical experimental sequence atoms in free fall Laser cooling/trapping preparation interferometer detection 100 ms 1s 20 ms 2T ~ 100 ms - 1s 40 ms t=0 time 9

10 Outline 1. Principle of Atom Interferometry 2. Cold Atom Gravimeters 3. Cold Atom Interferometer Gravity Gradiometry 10

11 Gravimeter: a vertical accelerometer Extinction PMO-3D Laser 1 Bring the two lasers in a copropagating way and retroreflect them on a mirror Detection Mirror Laser 2 Position of the equiphases defined by the mirror position atomic measurement = measure of the relative displacement atoms/mirror 11

12 Principle of measurement Free fall Doppler shift of the resonance condition of the Raman transition Ramping of the frequency difference to stay on resonance : π/2 π π /2 C 12

13 Principle of measurement Free fall Doppler shift of the resonance condition of the Raman transition Ramping of the frequency difference to stay on resonance : π/2 π π /2 Dark fringe : independent of T The g measurement is a frequency measurement 13

14 The SYRTE gravimeter 14

15 130 The whole instrument Laser system Drop chamber Control electronics, Power supplies 15

16 Sensitivity limits: vibrations Bruit de vibration (g.hz -1/2 ) 10-5 Plateforme OFF de jour Plateforme ON de nuit Fréquence (Hz) Typical noise in urban environnement Without isolation platform: g/hz 1/2 With platform: g/hz 1/2 GAIN : factor 40 Post-correction Seismometer v(t) f vib S PC Interferometer k eff gt² k eff gt² + f vib S Transition Probability Not corrected Corrected Number of shots Provides additional gain from 2 to 10 depending on vibration noise conditions: TYPICAL: g/hz 1/2 (urban, WB lab, Trappes)

17 Best short term sensitivity Side by side comparison between the CAG and an FG5X Performed in Walferdange (LUX) FG5X#216 (3 s cycling time) CAG CAG : Better immunity vs earthquakes 17 CAG : 5.7µGal@1s P. Gillot et al Metrologia 51 (2014)

18 Gravimetry lab at LNE Trappes 18

19 Continuous measurements 25 days of (almost) continuous measurement Concurrent operation of two intruments : CAG and igrav g (µgal) residuals (µgal) µgal= 10-8 ms -2 ~ 10-9 g CAG igrav Time (h) Data averaged over 400 CAG shots = 176 s Averaged over 1h Residuals 2 µgal ptp 19

20 Continuous measurements Long term stability of the residuals QUIET 1.5 day : White noise 1 nm.s -2 in 10000s Over 27 days: Flicker floor 2-3 nm.s -2 Typical stability at one day: µgal 20

21 igrav calibration One day to calibrate with an uncertainty of 1nm.s -2 (1 %0), 0.2%0 after 27d Comparing calibrations with FG5 vs CAG, 3 days of common view measurement FG5X CAG 21

22 7 years of measurement at Trappes Varying parameters Fixed parameters g (µgal) Chirp selection Intensities locked Coriolis MJD RMS fluctuations over the last year : 2.5 µgal 22

23 Accuracy 23

24 Accuracy Optics & cloud expansion 4 g (µgal) T at (µk) Need to limit the expansion of the cloud 24

25 Participating to ECAG 11 25

26 International comparisons ICAG 09 (BIPM) : CCM.G-K1 ECAG (2011, LUX) CAG Results Date Difference g CAG -g REF (µgal) CCM.G-K2 (2013, LUX) (7.8) (5.7) (5.5) 26 Two international Key comparisons 2009 & 2013 The first atomic gravimeter to participate All other instruments were corner-cube gravimeters

27 State of the art ground gravimeters Many groups are now working on the development of cold atom gravimeters LNE SYRTE WUHAN HUB 2T (ms) Sensitivity (/Hz 1/2 ) g g g Long term stability g g < g Accuracy g TBD g Differences in T (and thus in the scale factor) do not necessarily correlate with the performances Motivates the development of compact gravimeters (2T 100 ms) : Muquans, ONERA 27

28 Improving the accuracy Dominant systematics related to finite temperature of the atomic source Use of ultracold atoms Evaporative cooling in a dipole trap Atoms in the crossed dipole trap Investigate phase shift versus temperature (in the range 0.1-2µK) Extrapolate to T = 0 µk 28 Target accuracy : < 1µGal Current temperature: 200 nk

29 Outline 1. Principle of Atom Interferometry 2. Cold Atom Gravimeters 3. Cold Atom Interferometer Gravity Gradiometry 29

30 CAI Gravity Gradiometer o Simultaneous interferometers on two cold atom clouds with common Raman lasers o Differential measurement allows for extracting the acceleration difference and thus the Earth gravity gradient o Suppression of common mode noise, and in particular of the vibration noise o Adapted for onboard measurements

31 Measurement of G Stanford (M. Kasevich) Florence (G. Tino) Differential acceleration sensitivity demonstrated: g Statistical uncertainty: on G Overall uncertainty on G : Accuracy on G :?

32 CAI Gravity Gradiometer How to increase the sensitivity? High order Bragg diffraction LMBS with up to 100 photons Ultracold atoms (atom chips) With the parameters 2T = 500 ms, T C = 2 s N = 10 5, T = nk Δz = 1 m Differential sensitivity: s -2 = 0.1 E at 1s More than one order of magnitude better than state of the art 32

33 Why not going to space? Atoms are free falling, but the satellite also! Significant increase of T is possible, T = 5-10 s Less vibrations (non-inertial accelerations, such as due to drag) Limit in T arrises from the expansion of the atomic cloud o 1.8 µk: temperature limit of laser cooling for Rb atoms o 100 nk: typical temperature for an evaporatively cooled sample of atoms o 100 pk: requires decompression or DKC Temp s v s x (2T=2s) s x (2T=10s) 1.8 µk 1.2 cm/s 2.4 cm! 12 cm 100 nk 3 mm/s 6 mm 3 cm! 100 pk 0.1 mm/s 0.2 mm 1 mm 33

34 A proposal O. Carraz et al. (2014). A spaceborne gravity gradiometer concept based on cold atom interferometers for measuring Earth s gravity field, Microgravity Science and Technology 26(3), T = 10 s Double diffraction interferometer Two interferometers separated by 0.5 m Sensitivity in the s -2 (me) range 1 E = 10-9 s -2

35 Expected performances Comparison between classical (GOCE)/quantum concepts for a space gradiometer Benefit from atom interferometers: stability of the scale factor and good control of systematics => better long term stability 35

36 Other results/developments Metrology of atom gravimeters Investigation of systematic effects, impact of noise sources, comparisons: 18 papers in the last 10 years Technical developments Development of subsystems (laser, MW ): 4 papers Demonstration of new interferometer geometries Pyramid gravimeter => Industrial transfer, Muquans Q. Bodart et al., Appl. Phys. Lett. 96, (2010) Double diffraction => Space sensors (STE-QUEST, gradiometer) T. Lévèque et al., Phys. Rev. Lett. 103, (2009) Demonstration of new methods to cope with vibrations Correlation with classical sensors (sismometers, accelerometers) - Filtering & Post-correction => High sensitivity sensors J. Le Gouët et al., Appl. Phys B 92, 133 (2008) - Operation in the presence of large vibration noise (earthquakes) => Field applications S. Merlet et al., Metrologia 46, (2009) - Real time compensation & Hybridization of sensors => Inertial navigation J. Lautier et al., Appl. Phys. Lett. 105, (2014) - Signal extraction in differential sensors => Gradiometry F. Pereira Dos Santos, Phys. Rev. A 91, (2015) 36

37 Other experiments Gyrometer ForcaG On chip gyrometer lattice ICE: Onboard accelerometry Compact gravimeter: Muquans MIGA: Long baseline gradiometry STE-QUEST: Test of WEP

38 Atom Interferometry and Inertial Sensors Team at SYRTE PhD students Quentin Bodart Tristan Farah Pierre Gillot Mehdi Langlois Romain Karcher Romain Caldani People that have contributed to this work (since 2009) Post-docs Anne Louchet-Chauvet Christine Guerlin Bing Cheng Almazbek Imanaliev Azer Trimèche Staff Sébastien Merlet Franck Pereira dos Santos Arnaud Landragin

39 Fundings Gravimeter project supported mainly by LNE within the WB project Additional fundings : 39

40 40

41 Conclusion 3 years of calibration of the igrav, improving the CAG Fluctuation of the calibration?? CAG? igrav? (also seen with FG5X) Atom gravimeters show very good sensitivity are now ready for applications previously «reserved» to SG CAG improvement: decrease uncertainty to g ( g currently) improve the sensitivity with the igrav, continue the comon view analysis Continuous g measurements for years (25) nm.s -2

42 Phase difference between the two paths T L Gustavson et al., Class. Quantum Grav. 17 (2000). Rotation phase shift: Direction of atoms Two atomic sources of opposite directions Sum: acceleration Φ A Φ B Difference: rotation Source B Source A 42

43 Watt balance Goal : Measure Planck constant h with a 10-8 relative accuracy Interest : Replace the Kg etalon by a definition linked to h Static stage Dynamic stage j.dl B F Laplace = i L B B.i.L = m.g F g = m.g U B v U = B.L.v Josephson frequency Planck constant m g v = U i Accurate measurement of g is needed m k f g 2 J v h

44 Increasing the interaction time Increasing T increases - the intrinsic sensitivity (the scale factor) - the size of the experimental set up Release Vs Launched (fountain geometry) 2T H, release H, fountain 20 ms 0.5 cm 0.1 cm 160 ms 12.5 cm 3 cm 600 ms 1.8 m 45 cm 2 s 20 m 5 m A few ongoing projects of 10 m tall chambers 2.8 s 40 m 10 m Stanford Wuhan Hannover 44