Light Pulse Atom Interferometry for Precision Measurement Thank you very much for introducing me and I also thank the organizer for inviting me to this conference. From what I understood, this conference is focused on the gravitational-wave which would be extremely hard to detect in the experimental point of view. What I will talk about today is the atom interferometry using laser pulse and laser-cooled ultracold atoms and its application to precision measurement, especially on the gravity measurement. Jaewan Kim Myongji University

AI for Precision Measurements Inertial Sensing – Gravimeters, Gyroscopes, Gradiometers Newton’s constant G Fine-structure constant and h/M Test of Relativity Interferometers in space … There are many fields which atom interferometry can provide equally or better or sometimes unique opportunity in precision measurement. The gravity measurement is one of the field in which atom interferometers start to outperform other techniques. I am afraid that I can not talk about other things except gravimeters because my research was on the Gravimeters and 30 minutes is too short. I also hope that this talk can act as a rough introduction to the following two talks more focused on the gravitational wave detection.

Gravity Measurements Geophysics Gravity field mapping (crustal deformations, mass changes, definition of the geoid …) Navigation (submarine…) Tests of fundamental physics (equivalence principle, tests of gravitation …) g Metrology: Watt Balance (new definition of the kg)

Absolute Gravimeters Commercial Gravimeter : FG5 Atomic gravimeter Stanford experiment in 2001 : Resolution: 3 µGal after 1 minute Accuracy: <3 µGal From A. Peters, K.Y. Chung and S. Chu Principle : Michelson interferometer with falling corner cube Accuracy : 2 µGal 1 µGal = 10-8 m/s2 ~ 10-9g

Principle of Atom Interferometry

Stimulated Raman Transitions 3 level atoms Coherent beam splitter |F=2 = |b k2, 2 k1, 1 87Rb |5P3/2 780 nm |i > ωatome |F=1 = |a |5S1/2 keff = k1-k2 Mirror (p pulse) Two photon transition couple |a and |b Key advantage of Raman transitions - State labelling - Detection of the internal states Beam splitter (p/2 pulse)

Analogy : Optical/Atomic Interferometry Coherent splitting and recombination Two complementary output ports Intensity modulation Two momentum states Atomic Interferometer analogous to Mach-Zehnder Interferometer

Interferometer Phase Shift b - F Laser phase gets imprinted

Case of an Acceleration DF = F1(t1) – 2F2 (t2) + F3 (t3) =

Implementation of Raman Laser Vertical Raman lasers Retroreflect two (copropagating) Raman lasers Reduces influence of path fluctuations (common mode) 4 laser beams 2 pairs of counterpropragating Raman lasers with opposite keff wavevectors Position of planes of equal phase difference attached to position of retroreflecting mirror Laser 1 Pulse 1 Pulse 2 Pulse 3 Laser 2 Interferometer measurement = relative displacement atoms/mirror Miroir

Principle of Measurements 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~45%

Principle of Measurements 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~45% C~45%

Principle of Measurements 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~45%

Principle of Measurements 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~45% Dark fringe : independent of T

Experiments

Experimental Setup 2nd generation vacuum chamber Titanium vacuum chamber (non magnetic) 14 + 2 + 4 viewports Indium seals Pumps : 2 × getter pumps 50 l/s 1 × ion pump 2 l/s 4 × getter pills Two layers magnetic shield Retroreflecting mirror under vacuum

Experimental Setup

Experimental Setup Baking 2~3 months at 120 °C Commercial fiber splitters Fibered angled MOT collimators Symmetric detection Passive isolation platform Baking 2~3 months at 120 °C

Optical Bench Compact : 60 by 90 cm 3 ECDL, 2 TA Key feature : Use the same lasers for Cooling and Raman beams

Noise Parameters 2T=100 ms t = 6 µs sv ~ vr Ndet = 106 Tc = 250 ms Contrast ~ 45 % Sources of noise laser phase noise mirror vibrations detection noise SNR = 25 σΦ = 1/SNR = 40 mrad/shot sg/g = 10-7 /shot

Influence of Laser Phase Noise 2T=100 ms Source σΦ (mrad/shot) Laser s 100 MHz reference 1,0 Synthesis HF 0,7 PLL 1,6 Optical fiber Retroreflection 2,0 Total 3,1 σg (g/Hz1/2) 1,3·10-9 0,9·10-9 2,0·10-9 2,6·10-9 3,9·10-9 Negligible with respect to observed interferometer noise

Vibration Noise Measurement of the vibration noise with a very low noise seismometer (Guralp T40) @ 1s : 2,9 · 10-6 g ; 1,4 · 10-6 g ; 7,6 · 10-8 g OFF (day) OFF (night) ON (day)

Correlation : Gravimeter - Seismometer Us(t) velocity signal => Expected phase shift Platform on Platform Off Use the seismometer to correct the interferometer phase

Vibration Correction Seismometer PC keffgT² Post correction v(t) → fvibS Interferometer keffgT² + fvibS Typical sensitivity Without correction (day) : 8 10-8g @ 1 s With correction (night) : 5 10-8g @ 1 s With correction : 2-3 10-8g @ 1 s → Gain ~ 3 Best result Night – Air conditioning OFF With correction : 1.4 10-8g @ 1 s

Long Term Measurements 4 continuous days in April 2010 reveal earth tides

Long-Term Stability Allan standard deviation of tide-corrected gravity data 4 10-10g Long term stability comparable to the accuracy of the tide model

Wavefront Aberrations Wavefronts are not flat : gaussian beams, flatness of the optics … Case of a curvature → δφ = K.r2 (with K = k1/2R) Δg < 10-9 g with T = 2 µK  R > 10 km ! → flatness better than λ/300 !!! Measure aberrations with wavefront sensor + excellent optics + colder atoms

Characterization of Optics Mirror 40mm diameter PV= l/10 RMS =l/100 Simulation : T = 2.5mK s = 1.5mm g/g = 1.4 10-9 PV l/4 g/g = 8 10-9

Compact Atomic Gravimeter Principal demonstrations of key elements done New prototype under realization (automne 2010) High repetition rate (4 Hz) Expected performances: 50 µGal/√Hz Transportable device: field applications Pyramidal reflector (2X2 cm2) sensor head: Few dm3 no mechanical moving part Magnetic shield 30 cm Laser and electronic ensemble: 19 inches/12 U

Conclusion Laboratory experiment – (for Watt Balance project)  CAG Laboratory experiment – (for Watt Balance project) Aimed at ultimate accuracy <10-9g Need for ultra cold atoms  Towards on-field sensors Technology is now mature Transfer to industry First step : Miniatom Soon on the market? New schemes Trapped geometries : optical lattices, atom chips ? Further reduction in the size New applications Geophysics, fundamental physics (tests of EP, space missions …)