  Laser frequency noise is a dominant noise background for the detection of
gravitational waves using long-baseline optical interferometry. Amelioration of
this noise requires near simultaneous strain measurements on more than one
interferometer baseline, necessitating, for example, more than two satellites
for a space-based detector, or two interferometer arms for a ground-based
detector. We describe a new detection strategy based on recent advances in
optical atomic clocks and atom interferometry which can operate at
long-baselines and which is immune to laser frequency noise. Laser frequency
noise is suppressed because the signal arises strictly from the light
propagation time between two ensembles of atoms. This new class of sensor
allows sensitive gravitational wave detection with only a single baseline. This
approach also has practical applications in, for example, the development of
ultra-sensitive gravimeters and gravity gradiometers.
