Atom interferometry for fundamental physics and gravitational wave detection

In recent years, atom interferometry and atomic clocks have made impressive gains in sensitivity and time precision. The best atomic clocks have stability corresponding to a loss of less than one second in the lifetime of the universe. Matter wave interferometers have achieved record-breaking coherence times (seconds) and atomic wavepacket separations (over half a meter), resulting in a significant enhancement in accelerometer and gravity gradiometer sensitivity. Leveraging these advances, atomic sensors are now poised to become a powerful tool for discovery in fundamental physics. I will provide a detailed introduction to light-pulse atom interferometry, and explain various techniques that are being pursued to further enhance sensitivity. I will then discuss several specific applications, including direct detection of dark matter, tests of general relativity, searches for new forces, and gravitational wave detection. I will also describe a new type of atom interferometry based on narrow-line transitions in clock atoms that is central to the Mid-band Atomic Gravitational wave Interferometric Sensor (MAGIS) proposal, which is targeted to detect gravitational waves in a frequency band complementary to existing detectors (0.03 Hz – 10 Hz), the optimal frequency range to support multi-messenger astronomy. I will conclude with a brief discussion of MAGIS-100, a 100-meter tall atomic sensor now being constructed at Fermilab that will serve as a prototype of such a gravitational wave detector, and that will be sensitive to proposed ultra-light dark matter (scalar and vector couplings) at unprecedented levels.