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 highlight ongoing efforts to test aspects of general relativity and quantum mechanics, and search for new fundamental interactions.  A particularly exciting direction is gravitational wave detection.  I will describe 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.  Finally, I will discuss MAGIS-100, a 100-meter tall atomic sensor being constructed that will serve as a prototype of such a detector, and will also be sensitive to proposed ultra-light dark matter (scalar and vector couplings) at unprecedented levels.