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Geodätische Woche - 9th October 2014
Terrestrial Gravity Measurements with the mobile Atom Interferometer GAIN
Christian Freier
Matthias Hauth Vladimir Schkolnik
Achim Peters
AG Optische Metrologie Humboldt-Universität zu Berlin
Graphics by IQO Hannover
Geodätische Woche - 9th October 2014
Gravity Variations on Earth
Gravitational effects Magnitude
Geographical gravity variations
Global scale ~ 10-3 g
Regional scale ~ 10-6 g
Basic tidal effect ~ 10-7 g
Man-made changes
New buildings ~ 10-8 g
Trains, people, … ~ 10-9 g
Geological effects
Tectonic plate movements ~ 10-9 g
Atmospheric pressure ~ 3 x 10-10 g / mbar
Free air gravity gradiant ~ 3 x 10-9 g / cm
- Buildings
- People
- Plate tectonics
- Volcanology
Graphic by GOCE
- Geodesist g ≅ 9.81m
s2≅ 109μGal
Geodätische Woche - 9th October 2014
State-of-the-Art Gravimeters
Relative Absolute
Spring/ Mass
Super-conducting
Falling Corner Cube
Noise [g/Hz] 2 x 10-9 2 x 10-10 ~ 4 x 10-8
Drift [g/Day] 1 x 10-8 1 x 10-11 -
Accuracy [g] - - ~ 2 x 10-9
Unique feature Small, Robust,
Flexible Extremely high
precision Absolute Value
Example
Geodätische Woche - 9th October 2014
State-of-the-Art Gravimeters
Relative Absolute
Spring/ Mass
Super-conducting
Falling Corner Cube
Noise [g/Hz] 2 x 10-9 2 x 10-10 ~ 4 x 10-8
Drift [g/Day] 1 x 10-8 1 x 10-11 -
Accuracy [g] - - ~ 2 x 10-9
Unique feature Small, Robust,
Flexible Extremely high
precision Absolute Value
Example
One gravimeter for all purposes !?
Geodätische Woche - 9th October 2014
Atom Interferometry
Interferometry Sequence
F1 – Ground State F2 – Excited State
Geodätische Woche - 9th October 2014
Atom Interferometry
Population of excited state after pulse sequence
Interferometry Sequence
F1 – Ground State F2 – Excited State
Geodätische Woche - 9th October 2014
Atom Interferometry
Population of excited state after pulse sequence
Interferometry Sequence
F1 – Ground State F2 – Excited State
𝑃𝐹2 = 𝑃 + 𝐶2 cos ∆𝜙
Acceleration term: ∆𝜙 ∝ 𝑘 𝑔 𝑇2
∆𝜙 = 𝜙3 − 2𝜙2 + 𝜙1
Geodätische Woche - 9th October 2014
Electronics and optics Physics-package
Mobile Atom Interferometer GAIN (Gravimetric Atom Interferometer)
Targeted Performance:
Sensitivity
10−8 g Hz
Accuracy: 5 × 10−10 g
• Mobile setup
• Atomic fountain ℎ ≅ 0.7m 𝑇 ≤ 0.3𝑠
• Rubidium 87
• Diode Laser System @ 780nm
Geodätische Woche - 9th October 2014
0.7 Hz
Experimental Sequence
~ 108 Rb87 atoms trapped within 0.6s
1. Trap loading & launch
2. State selection
3. Interferometry sequence
4. Detection via fluorescence
Geodätische Woche - 9th October 2014
0.7 Hz
Experimental Sequence
1. Trap loading & launch
2. State selection
3. Interferometry sequence
4. Detection via fluorescence
Geodätische Woche - 9th October 2014
Experimental Sequence
1. Trap loading & launch
2. State selection
3. Interferometry sequence
4. Detection via fluorescence
0.7 Hz
Geodätische Woche - 9th October 2014
Experimental Sequence
1. Trap loading & launch
2. State selection
3. Interferometry sequence
4. Detection via fluorescence
0.7 Hz
Geodätische Woche - 9th October 2014
Experimental Sequence
1. Trap loading & launch
2. State selection
3. Interferometry sequence
4. Detection via fluorescence
0.7 Hz
Geodätische Woche - 9th October 2014
E F’=3
F’=2
F’=1 F’=0
F=2
F=1
Dete
ctio
n
Repum
per
Experimental Sequence
F2
F1+F2
Inte
nsi
ty /
a.u
.
Time / a.u.
𝑃𝐹2 = 𝑃 + 𝐶2 cos ∆𝜙 ∆𝜙 ∝ 𝑘 𝑔 𝑇2
1. Trap loading & launch
2. State selection
3. Interferometry sequence
4. Detection via fluorescence
0.7 Hz
Geodätische Woche - 9th October 2014
1st Mobile Measurement
550km Transport by Road
Berlin Adlershof
Geodetic Observatory Wettzell
openstreetmap.org
Geodätische Woche - 9th October 2014
1st Mobile Measurement
• Geodetic Observatory Wettzell (BKG)
• Transport from Berlin (small truck)
• 3 day set-up time at new site
• 2 weeks of gravity recordings
• Simultaneous operation of super-conducting gravimeter SG30 on site
SG30 GAIN
Measured by GAIN:
• Tidal gravity variation
• Excellent agreement with model
• Reliable operation with few gaps in data set
Published in proc. of Proceedings of the International School of Physics Enrico Fermi Course CLXXXVIII on Atom Interferometry
Geodätische Woche - 9th October 2014
1st Mobile Measurement
• Upper Graph: without air pressure correction
• Lower Graph: with air pressure correction
• Excellent agreement, no observable drift
Published in proc. of Proceedings of the International School of Physics Enrico Fermi Course CLXXXVIII on Atom Interferometry
GAIN (blue) SG30 (black)
Geodätische Woche - 9th October 2014
1st Mobile Measurement
• Upper Graph: without air pressure correction
• Lower Graph: with air pressure correction
• Excellent agreement, no observable drift
Published in proc. of Proceedings of the International School of Physics Enrico Fermi Course CLXXXVIII on Atom Interferometry
GAIN (blue) SG30 (black)
• Allan Standard Deviation GAIN vs. SG30
• Blue: previous SG30 scale factor
• Green: SG30 scale factor recalibrated using this dataset
Geodätische Woche - 9th October 2014
1st Mobile Measurement
• Upper Graph: without air pressure correction
• Lower Graph: with air pressure correction
• Excellent agreement, no observable drift
Published in proc. of Proceedings of the International School of Physics Enrico Fermi Course CLXXXVIII on Atom Interferometry
GAIN (blue) SG30 (black)
• Allan Standard Deviation GAIN vs. SG30
• Blue: previous SG30 scale factor
• Green: SG30 scale factor recalibrated using this dataset
Geodätische Woche - 9th October 2014
Performance Overview
Performance Targeted Achieved Status
Sensitivity
intrinsic noise only •Fulfilled by laser phase noise
including realistic vibrational conditions
•Limited by vibration isolator performance
Stability
Bias Stability 5 . 10-10 g <5 . 10-10 g •Fulfilled
Absolute accuracy 5 . 10-10 g 1 . 10-8 g •analysis of systematic effects in progress
Geodätische Woche - 9th October 2014
Transport – Measurement - Transport
Gravity measurements:
• Sensitivity of 0.6 . 10-9g after one hour
• Allan standard deviation in the low 10-10g level
• Demonstrated mobile, continuous gravity recordings
• Sensitivity comparable to best spring-based gravimeters but without long-term drift
• Recalibration of superconducting gravimeter scale factor
Mobile setup: completed
Summary
Geodätische Woche - 9th October 2014
Outlook
Onsala Space Obsorvatory (Chalmers University of Technology) • Absolute accuracy of gravity value - further compensation of systematics
• Measurements at other locations (e.g. Onsala Space Observatory)
• Simultaneous recording of both g and the gravity gradient
• Tests for Non-Newtonian gravitational forces
Setup Improvements
Pumped Storage Reservoir in Hornberg,De
Geodätische Woche - 9th October 2014
http://www.physik.hu-berlin.de/qom
Thank you for your attention
Questions ?
Special thanks to the staff of the IfE and the BKG for their cooperation
Geodätische Woche - 9th October 2014
Active Vibration Isolation Stage
Freier, Measurement of Local Gravity using Atom Interferometry, Humboldt Universität zu Berlin (2010), Diplomarbeit
Geodätische Woche - 9th October 2014
Tilt and Coriolis Compensation
back-coupling into the Raman-fibre
Tilt-Compensator
Raman beams
• Raman retro-reflector on piezo tip/tilt stage with sub-μrad precision and closed-loop actor
• Active Raman beam alignment during
gravimeter measurements
• Suppression of Coriolis effects during interferometer sequence
Coriolis Effect suppression
Hauth et al., Applied Physics B, 113 (2013) 49
Geodätische Woche - 9th October 2014
Atom Interferometry
Raman Pulses
| g , 0ħk >
| e, + 2ħk >
| i, + 1ħk >
Laser 1 Laser 2 v
v
Π-Pulse
v
v
Π/2-Pulse
mirror beamsplitter
DE
Geodätische Woche - 9th October 2014
Mobile atom interferometer GAIN (Gravimetric Atom Interferometer)
Determing gravitational acceleration
Geodätische Woche - 9th October 2014
Mobile atom interferometer GAIN (Gravimetric Atom Interferometer)
Laserfrequencies
permanently correct for the dopplereffect
Over a time T this chirp
causes a phase shift Φchirp
Calculation of g
Φfringe
Φchirp + Φfringe = k g T²
Geodätische Woche - 9th October 2014
Table of Systematic Effects
without
correction
with
correction
Wavefront Distortions -50 0 +- 50
Sync Vibrations 90 0 +- 80
Coriolis Effects 100 0 +- 15
RF Groupdelays 100 0 +- 10
AC-Stark Shift (1PLS) 1000 0 +- 5
Self Gravitation 19 0 +- 5
Quadratic Zeeman shift 0 0 +- 5
Rb Vapor Pressure 5 0 +- 3
Ref-Frequenz -10 0 +- 2
AC-Stark Shift (2PLS) 0 0 +- 2
vertical alignment 0 0 +- 1
Total Uncertainty 97
Systematic Effect Magnitude [nm/s²] uncertainty
[nm/s²]