Transcript Measuring the Earth`s gravity field with cold atom

Measuring the Earth’s gravity field with cold
atom interferometers
Olivier Carraz, Christian Siemes, Luca Massotti,
Roger Haagmans, Pierluigi Silvestrin
Paris, France
28/11/2014
Earth Gravity Field
What is needed in the near future?
Future
Concepts?
Cold Atom Physics
1. Why cold atoms?
a.
Study/observe internal structure of free atoms (≠ solid state
physics)
b.
Atom waves potentially more interesting than electron or neutron
waves (neutral + rich internal structure)
c.
Interaction with external electric fields and gravity
2. BUT: RT atom speeds ~ 300 m/s
a.
Atom beams have low coherence  difficult to handle as waves
b.
Limited observation time (few ms) on a table-top experiment
h
ldB =
p
DxDp ~
3. Low temperature physics
a.
4K (LHe) He thermal velocity ~ 90 m/s
b.
Cryopump effect: condensation  no gas phase
4. Laser cooling techniques:
a.
Magneto Optical Traps (MOT) < 10µK ~ cm/s
b.
Adiabatic Expansion
c.
Raman Cooling
d.
Velocity Selective Coherent Population Trapping
e.
Evaporative cooling in magnetic or optical traps ~ 100nK
f.
Sympathetic cooling (involving more than one species)
Velocity-distribution data of a gas of rubidium
atoms, confirming the discovery of a new
phase of matter, the Bose–Einstein
condensate.
AI Gravimeter : How does it work ?
Free fall of an object
- Inertial reference : Earth
- Free fall of an object in the inertial reference
- ‘Measurement’ of the free falling ...
z
g
d 2z
 g
2
dt
EARTH
Here
- Object : Cold atoms in the vacuum
- Measurement of the free falling by atomic interferometry ...
Atom interferometry
Matter wave
Louis De Broglie (1924)
Louis de Broglie
Nobel Price 1929
a.
Waves phenomena for matter:
–
–
b.
Young experiment realised
with cold atoms at NIST
Diffraction
Interferences
Interferences : Atoms have different paths to follow
Stimulated Raman transition
Coherent transfert of population
Control the transfert from state a to state b
i
b (t )
a
b
-pulse
Probability
Energy
1
0
ab
Temps
Rabi Oscillation
b
a
t
a
2
/2-pulse
Coherent
superposition
Stimulated Raman transition
Coherent transfert of population
i
Give an important and directive recoil pulse
Energy
Contrapropagating Lasers
b
a
For Rb, 2.vrec ~ 12 mm.s-1
Principle of an AI gravimeter
1. Chu-Bordé Configuration :
p
2
-p -
p
2
The phase of the laser is printed on
the phase of the atoms during Raman
transitions : Stationary wave
referenced to the mirror
2. Interferometric signal :
1

1  cos  
N

 a
2

1
 N b  1  cos  
2

  keff gT 2
sg =
1
1 1
.
. 2
SNR keff T
AI Performances
Gyroscope – Gradiometer : Raman in
common mode
z
Gyroscope : 2 accelerometers with physical
surface rejecting acceleration in differential
mode
FgFW
FgFW
/2

/2
z
x
Fg2
Gradiometer : 2 gravimeters rejecting common
vibrations of the miror.
Fg1
/2

/2
t
Concept of an AI inertial sensor for
space : 1D
z
Fg1
Fg2
v
-v
Fg3
Fg4
v
-v
/2

/2
y
CAI GG Concept – design for one axis
Gravity gradiometer (Vzz – wx2 – wy2), gyroscope (wx), accelerometer (az)
CAI GG Concept – design for three axes
Gravity gradiometer (Vzz – wx2 – wy2), gyroscope (wx), accelerometer (az)
Theoretical performance:
(V+Ω2)  4.7 mE / sqrt(Hz)
Ω  35 prad/s / sqrt(Hz)
a  2 pm/s2 / sqrt(Hz)
Ambiguity due to phase jumps:
(V+Ω2)  16 E
Ω  160 nrad/s
a  7.8 nm/s2
CAI GG Concept – simulations
by Christian Siemes (email:
[email protected])
Earth System Model
http://www.gfz-potsdam.de/en/research/organizational-units/departments-ofthe-gfz/department-1/earth-system-modelling/services/esaesm/
Instrument noise
•
4.7 mE/sqrt(Hz) GG
•
2 cm orbit
•
100 nrad attitude (STR and CAI GG)
Background model errors
•
10% AO … time-variable gravity field
•
10% AOHIS … mean gravity field
•
EOT11a – GOT4.7 (8 major tidal constituents)
GRACE Science Team Meeting 2014, Potsdam (Germany)
CAI GG Concept – simulations
by Christian Siemes (email:
[email protected])
Time variable gravity field
Orbit: 31 day repeat, a = 400 km, e = 0.001, i = 89o
•
Modelling error … relevant
 Mean
 Omission
GRACE Science Team Meeting 2014, Potsdam (Germany)
CAI GG Concept – simulations
by Christian Siemes (email:
[email protected])
Time variable gravity field
Orbit: 31 day repeat, a = 400 km, e = 0.001, i = 89o
•
•
•
•
•
•
Modelling error … relevant
Position noise … negligible
Attitude noise … negligible
AO error … relevant
OT error … relevant
GG noise … bottle neck
GRACE Science Team Meeting 2014, Potsdam (Germany)
CAI GG Concept – simulations
by Christian Siemes (email:
[email protected])
Mean gravity field
Orbit: 61 day repeat, a = 250 km, e = 0.001, i = 89o
GRACE Science Team Meeting 2014, Potsdam (Germany)
Hybridization Classical/Quantum
sensors
Hybridization Classical/Quantum
sensors
Electro-static
Accelerometer
Hybridization Classical/Quantum
sensors
Benefits of the performance of electro static accelerometers at high
frequency.
Calibration for long term measurements.
Compacity
Hybridization Classical/Quantum
sensors
J. Lautier, L. Volodimer, T. Hardin, S. Merlet, M. Lours,
F. Pereira Dos Santos, and A. Landragin
"Hybridizing matter-wave and classical accelerometers”
Appl. Phys. Lett. 105, 144102 (2014)
CAI GG Concept – studies
Running studies:
- Compact Vacuum chamber for an Earth Gravity Gradiometer based on
Laser-Cooled Atom Interferometry (2014)
Planned studies
- Study of a Cold-Atom interferometry gravity gradiometer sensor and
mission concept (KO ~ 2014)
- Development of Cooling/Raman Laser source with enhanced operational
features (KO ~ 2015)
- Development of phase and frequency modulators for atom sensor systems
- Hybrid Atom Electrostatic System for Satellite Geodesy (KO ~ 2015)
Conclusion & Outlook
1. Future challenging gravity mission (Mass distribution and mass
transport)
a.
Explore deeper the Earth
b.
Comprehension of other planets
2. Different concepts for measuring Geoid
a.
Satellite ranging
b.
Gravity gradiometer
3. Atom interferometry can improve both techniques
a.
Hybridization classical accelerometers/AI
b.
Cold atom gradiometer