Mid-band gravitational wave detection with precision atomic sensors

TL;DR

The paper proposes MAGIS, a two-satellite mid-band gravitational wave detector using precision Sr atom sensors in medium Earth orbit to fill the gap between LISA and LIGO. It outlines a differential atom-interferometer measurement strategy that supports both broadband and resonant operation, enabling flexible observing modes. The science case spans white-dwarf, stellar-mass black hole, neutron star, and intermediate-mass black hole binaries, as well as cosmological gravitational waves and ultralight dark matter, with potential for early warning and multi-messenger astronomy. The work demonstrates feasibility while highlighting the need for further atomic-physics demonstrations and mission-level optimization and validation.

Abstract

We assess the science reach and technical feasibility of a satellite mission based on precision atomic sensors configured to detect gravitational radiation. Conceptual advances in the past three years indicate that a two-satellite constellation with science payloads consisting of atomic sensors based on laser cooled atomic Sr can achieve scientifically interesting gravitational wave strain sensitivities in a frequency band between the LISA and LIGO detectors, roughly 30 mHz to 10 Hz. The discovery potential of the proposed instrument ranges from from observation of new astrophysical sources (e.g. black hole and neutron star binaries) to searches for cosmological sources of stochastic gravitational radiation and searches for dark matter.

Figures (4)

• Figure 1: MAGIS gravitational wave sensitivity. Two example resonant sensitivity curves (at arbitrarily chosen frequencies) and the broadband mode sensitivity are shown in solid, thick black. The envelope of the possible resonant curves is shown by the lower brown boundary/line (this is the appropriate curve to compare to for discovery of longer-lived sources such as WD and NS binaries). The dashed gray curve is the appropriate, approximate sensitivity curve for the discoverability (though not the ultimate measurement SNR) of shorter-lived sources such as the LIGO BH binaries. The LISA strain curve is shown for reference Bender1998larson2000sensitivity. The Advanced LIGO curve is the design sensitivity smith2009path (not current sensitivity TheLIGOScientific:2016agk). Two black hole merger events observed by LIGO are shown in red. A WD-WD binary at 20 Mpc (with masses $0.5 M_\odot - 0.5 M_\odot$) is shown in green. A NS-NS binary at 200 Mpc (with masses $1.4 M_\odot - 1.4 M_\odot$) is shown in blue. Note that at frequencies in LIGO's band near the merger, the post-Newtonian formula we have used to draw these source curves breaks down. The dots on the GW150914, GW151226 and NS-NS 200 Mpc curves indicate remaining lifetimes of 10 yrs, 1 yr and 0.1 yrs (reading left to right). Degree scale sky localization appears feasible for in-spiraling sources.
• Figure 2: A space-time diagram of an example atom interferometer detector sequence for the proposed MAGIS detector. The detector consists of two atom interferometers based on single-photon transitions, one at position $x_1$ and the other at $x_2 = x_1+L$, where $L$ is the baseline distance. The trajectories of the atoms are shown in blue for the ground state and red for the excited state. Pulses of light (thin gray lines) are sent back and forth from each end of the baseline and interact with the atoms (interactions shown as black dots), transferring momentum to the atoms and changing their internal state. Whether or not an interaction occurs is controlled by matching the frequency of the light pulses to the Doppler shift of the atoms. The sequence shown consists of two single-photon transitions for each atom optic ($n=2$, $2\hbar k$ momentum transferred) and a resonant enhancement of $Q=4$ (four diamonds). The amount of resonant enhancement can be varied as needed by changing the pulse sequence.
• Figure 3: Schematic of the proposed design. M1 and M2 are the master lasers, with beams depicted as dotted and solid lines, respectively. The reference beams propagating between the satellites are denoted R1 (dotted) and R2 (solid) and originate from telescopes each each satellite. LO1 and LO2 are local oscillator lasers (dashed beam lines) that are phase locked to the incoming reference laser beams (R2 and R1, respectively). PD1 (PD2) is a photodetector used to measure the heterodyne beatnote between the incoming reference beam R2 (R1) and the local oscillator laser LO1 (LO2) in order to provide feedback for the laser link. BS is a (non-polarizing) beam splitter where the heterodyne beatnote is formed. Tip-tilt mirrors (TTM) allow for fine control of the pointing direction of each laser. All adjacent parallel beams are nominally overlapped, but for clarity they are shown here with a small offset.
• Figure 4: Mission orbit analysis. (a) GMAT simulation output showing the circular, geocentric orbits of the two spacecraft. (b) Relative velocity of the spacecraft along the direction of the baseline. (c) Angle of the orbital plane of the spacecraft with respect to the ecliptic over one year. Variation of the orbital plane is beneficial for avoiding detector blind spots.