1. 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

2. 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.

3. 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)

4. 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

5. Principle of Atom Interferometry

6. 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)

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

8. Interferometer Phase Shiftb
- F
Laser phase gets imprinted

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

10. 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

11. 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%

12. 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%

13. 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%

14. 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

15. Experiments

16. Experimental Setup 2nd generation vacuum chamber
Titanium vacuum chamber (non magnetic)
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

17. Experimental Setup

18. 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

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

20. 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

21. 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

22. 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)

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

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

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

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

27. 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

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

29. 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

30. 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 …)