Jason M. Hogan, David M. S. Johnson, Susannah Dickerson, Tim Kovachy, Alex Sugarbaker, Sheng-wey Chiow, Peter W. Graham, Mark A. Kasevich, Babak Saif, Surjeet Rajendran, Philippe Bouyer, Bernard D. Seery, Lee Feinberg, Ritva Keski-Kuha

An Atomic Gravitational Wave InterferometricSensor in Low Earth Orbit (AGIS-LEO)

AcknowledgmentsTK acknowledges support from the Hertz Foundation. TK, SD and AS acknowledge support from the NSF GRFP. AS acknowledges support from the SGF and a DoD NDSEG Fellowship. SR is supported by the DoE Office of Nuclear Physics under grant DE-FG02-94ER40818 and by NSF grant PHY-0600465. PB acknowledges support from a Fulbright Fellowship and the iXCore Foundation.

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• Shorter baselines allow for rigid structure → Mitigates rotation biases → Shields interferometer region from magnetic fields and sunlight → Facilitates more-complicated interferometer configurations (booms on multiple axes) → Single atom source for multiple axes, with retroreflectors for optical beams

Short-Baseline Configurations

Lattice-Hold Interferometer• Use optical lattices to continuously control the trajectories of the two arms of an interferometer• Smaller beams → larger intensities as required for lattice-hold atom manipulations• Gravitational-wave-induced phase shift:

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Space-time diagram forlattice-hold interferometer

Systematic Error ModelLeader-Follower (LF) Inclined-Great-Circles (IGC)

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Further systematics from both the instrument (laser wavefront aberrations, phase noise, and pointing jitter) and the low Earth orbit environment (magnetic fields and gravity gradients) appear manageable at the desired levels.

Semi-classical phase shift analysis for both configurations

Orbital Configurations

Leader-Follower (LF)• Baseline length constant• Rotation rate constant• Requires Earth’s shadow

Inclined-Great-Circles (IGC)• Length of baseline varies• Baseline Orientation (nearly) fixed → Reduced rotation effects

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Sensitivity to Gravitational WavesShot-noise-limited strain sensitivity with a five-pulse sequence

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Atom Interferometry• Light-pulse atom interferometry → Coherent splitting of the atom wavefunction with light pulses transfers momentum ħkeff to part of the atom → Atom follows superposition of two spatially separated free-fall paths → Phase shift induced by a gravity wave affects the interference pattern resulting from the recombination of the atom wavefunction

• Five-pulse sequence (π/2 - π - π - π - π/2) → Beamsplitter momenta can be chosen for symmetry and closure of the interferometer in a strong rotation bias → Insensitive to acceleration and gravity gradients

Gravitational Wave Phase Shift:

Space-time diagrams forfive-pulse sequence

Gravitational Wave Detector Concept

• Two satellites separated by ~30 km baseline• Atom interferometers near each satellite• Common interferometer lasers enlarged by telescopes on each satellite → Same beamline for fluorescence imaging• Atoms shuttled into place with optical lattice

IntroductionWe propose an atom interferometer gravitational wave detector in low Earth orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of atom interferometers separated over a ~ 30 km baseline. In the proposed configuration, one or three of these interferometer pairs are simultaneously operated through the use of two or three satellites in formation flight. The three satellite configuration allows for the increased suppression of multiple noise sources and for the detection of stochastic gravitational wave signals. The mission will offer a strain sensitivity of less than 10-18 / √Hz in the 50 mHz - 10 Hz frequency range, providing access to a rich scientific region with substan-tial discovery potential. This band is not currently addressed with the LIGO or LISA instruments. We also present a brief conceptual overview of shorter-baseline configurations (< 100 m) that could be deployed on the International Space Station or on an independent satellite.