DUSEL Atom Interferometric Gravity Wave Detector

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DUSEL Atom Interferometric Gravity Wave Detector

• Prof. Mark Kasevich
• Dept. of Physics and Applied Physics
• Stanford University, Stanford CA

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Collaborators, Stanford

• Experiment
• Jason Hogan
• David Johnson
• Alex Sugarbaker
• Theory
• Surjeet Rajendran
• Peter Graham
• Savas Dimopoulos

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Gravity Waves Introduction
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Gravity Waves Introduction
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Gravity wave sources
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Outline
de Broglie wave interferometry Overview of
previously demonstrated sensors (brief) Gravity
wave detection with AI Theory Terrestrial
(DUSEL) detectors Development of prototype
detector Equivalence Principle/Tests of
GR Gravity wave detection test-bed Programatics
for possible DUSEL facility
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(Light-pulse) atom interferometry
Resonant optical interaction
Recoil diagram
Momentum conservation between atom and laser
light field (recoil effects) leads to spatial
separation of atomic wavepackets.
2?
1?
2-level atom
Resonant traveling wave optical excitation,
(wavelength l)
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Semi-classical approximation
Three contributions to interferometer phase shift
Propagation shift
Laser fields (Raman interaction)
Wavepacket separation at detection
See Bongs, et al., quant-ph/0204102 (April 2002)
also App. Phys. B, 2006.
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Approximate Kinematic Model
Falling rock
Falling atom

• Distances measured in terms of phases ?(t1),
  ?(t2) and ?(t3) of optical laser field at
  position where atom interacts with laser beam
• Atomic physics processes yield
  a ?(t1)-2?(t2)?(t3)

• Determine trajectory curvature with three
  distance measurements ?(t1), ?(t2) and ?(t3)
  
  
• For curvature induced by acceleration a,
  a ?(t1) - 2?(t2) ?(t3)

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NGA MAGGPI Differential Accelerometer
Differential accelerometer, horizontal
configuration
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NGA MAGGPI Gravity Gradiometer
Demonstrated accelerometer resolution 6x10-12 g.
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Navy/SP-24 Hybrid Sensor
Raman interrogation demonstrated in PINS Phase I
gyro.
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DARPA PINS
GG sensor head
control/laser frames
optical
sensor electronics
GG amplifier electronics
electrical
GG amplifier laser
F3 master laser
F3 master electronics
DSP/DDS
F4 master electronics
F4 master laser
AG amplifier laser
AG amplifier electronics
power supply
AG sensor head
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Gravity wave detection
Metric
Differential accelerometer configuration for
gravity wave detection. Atoms provide inertially
decoupled references (analogous to mirrors in
LIGO) Gravity wave phase shift through
propagation of optical fields.
Gravity wave induced phase shift
h is strain, L is separation, T is pulse
separation time, w is frequency of wave
Previous work B. Lamine, et al., Eur. Phys. J. D
20, (2002) R. Chiao, et al., J. Mod. Opt. 51,
(2004) S. Foffa, et al., Phys. Rev. D 73,
(2006) A. Roura, et al., Phys. Rev. D 73,
(2006) P. Delva, Phys. Lett. A 357 (2006) G.
Tino, et al., Class. Quant. Grav. 24 (2007).
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Calculation Methodology

• Preliminary
• Define metric
• Calculate geodesic equations for photons and
  atoms
• Atom interferometer phase shift
• Initial coordinates for optical pulses, atom
  trajectories
• Find intersection coordinates for atom and photon
  geodesics (2 photons for Raman transitions)
• Evaluate scalar propagation phase
• Coordinate transformation to local Lorentz frame
  at each atom/photon intersection (Equivalence
  Principle) to for atom/photon interaction (eg.
  apply Sch. Eq.).
• Coordinate transformation to local Lorentz frame
  at final interferometer pulse to evaluate
  separation phase

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DUSEL/Terrestrial
1 km
Pre-print available indicating analysis details.

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Terrestrial detector sensitivity to stochastic
sources
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Technical challenges laser frequency stability

• Laser phase/frequency fluctuations result in
  spurious, but controllable, phase shifs.

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Technical challenges Seismic noise
Seismic noise induced strain analysis for LIGO.
From Thorne and Hughes, PRD 58
Seismic fluctuations give rise to Newtonian
gravity gradients which can not be shielded.
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DUSEL Preliminary Seismic Measurements
Data courtesy of Vuc Mandic.
PRELIMINARY
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Technical challenges atomic optics

• Advanced, high flux atom source development
• high rep rate, high flux source of cold atoms
• 10 Hz, 108 atoms/shot
• requires incremental advances in current
  technology
• Large momentum transfer atom optics
• Enhances sensitivity
• Demonstrated N 10
• Desired N 100
• Work in progress

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Stanford prototype in development
10 m tower apparatus to test Einstein
EP. Proving ground for AI techniques required
for DUSEL instrument. Expect first signals by
end of 08.
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Equivalence Principle
Use atom interferometric differential
accelerometer to test EP
10 m atom drop tower
Co-falling 85Rb and 87Rb ensembles Evaporatively
cool to lt 1 mK to enforce tight control over
kinematic degrees of freedom Statistical
sensitivity dg 10-15 g with 1 month data
collection Systematic uncertainty dg 10-16 g
limited by magnetic field inhomogeneities and
gravity anomalies.
Atomic source
10 m drop tower
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Development Tasks

• Refine seismic analysis and models to assess
  operating band and sensitivity limits of DUSEL
  located detector.
• 6 mo. effort
• Advance required atom optics instrumentation
• work in progress at Stanford EP 10 m facility
• 3 yr. effort
• Refined DUSEL facility requirements
• installation conceptual designs
• 6 mo. effort

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Costs and Funding

• AI instrument costs
• 2-3M, based on development costs for current
  hardware
• DUSEL facility costs
• ?
• Funding sources
• funds are currently being sought from NSF for
  atom optics development work

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Infrastructure requirements

• Power
• 10 kW
• Thermal
• 1 deg C temp control in laser rack area
• Space
• 2x 15 m x 5 m x 5 m AI instrument rooms,
  separated by 1 km
• magnetic shields required for interaction region
• 30 cm dia vertical shaft, evacuated to 10-6
  torr
• no magnetic shielding required in this area
• Laser/instrumentation bay
• 2 8 racks
• Seismic
• ultra-low vibration(!). Suitable distances from
  moving masses in 1 Hz band .

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Infrastructure requirements (cont)

• HVAC
• class 10,000 in atom/laser area.