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
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 √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).
We show that, by simple modifications of the usual three-level Λ-type scheme used for obtaining electromagnetically induced transparency (EIT), phase dependence in the response of the atomic medium to a weak probe field can be introduced. This gives rise to phase dependent susceptibility. By properly controlling phase and amplitudes of the drive fields we obtain variety of interesting effects. On one hand we obtain phase control of the group velocity of a probe field passing through medium to the extent that continuous tuning of the group velocity from subluminal to superluminal and back is possible. While on the other hand, by choosing one of the drive fields to be a standing wave field inside a cavity, we obtain sub-wavelength localization of moving atoms passing through the cavity field.
The inversionless free electron laser having a drift region consisting of two magnets is analyzed. Performing numerical simulations of electron motion inside wigglers and drift region, we have shown that this system has a positive mean gain over the entire energy distribution of the electron beam. We study the influence of emittance and the spread of electron energies on the gain in small- and high-gain regimes.