  Quantum entanglement has the potential to revolutionize the entire field of
interferometric sensing by providing many orders of magnitude improvement in
interferometer sensitivity. The quantum-entangled particle interferometer
approach is very general and applies to many types of interferometers. In
particular, without nonlocal entanglement, a generic classical interferometer
has a statistical-sampling shot-noise limited sensitivity that scales like
$1/\sqrt{N}$, where $N$ is the number of particles passing through the
interferometer per unit time. However, if carefully prepared quantum
correlations are engineered between the particles, then the interferometer
sensitivity improves by a factor of $\sqrt{N}$ to scale like 1/N, which is the
limit imposed by the Heisenberg Uncertainty Principle. For optical
interferometers operating at milliwatts of optical power, this quantum
sensitivity boost corresponds to an eight-order-of-magnitude improvement of
signal to noise. This effect can translate into a tremendous science pay-off
for space missions. For example, one application of this new effect is to fiber
optical gyroscopes for deep-space inertial guidance and tests of General
Relativity (Gravity Probe B). Another application is to ground and orbiting
optical interferometers for gravity wave detection, Laser Interferometer
Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna
(LISA), respectively. Other applications are to Satellite-to-Satellite laser
Interferometry (SSI) proposed for the next generation Gravity Recovery And
Climate Experiment (GRACE II).
