3 research outputs found
Magneto-optical rotation and cross-phase modulation via coherently driven tripod atoms
We study the interaction of a weak probe field, having two orthogonally
polarized components, with an optically dense medium of four-level atoms in a
tripod configuration. In the presence of a coherent driving laser,
electromagnetically induced transparency is attained in the medium,
dramatically enhancing its linear as well as nonlinear dispersion while
simultaneously suppressing the probe field absorption. We present the
semiclassical and fully quantum analysis of the system. We propose an
experimentally feasible setup that can induce large Faraday rotation of the
probe field polarization and therefore be used for ultra-sensitive optical
magnetometry. We then study the Kerr nonlinear coupling between the two
components of the probe, demonstrating a novel regime of symmetric, extremely
efficient cross-phase modulation, capable of fully entangling two single-photon
pulses. This scheme may thus pave the way to photon-based quantum information
applications, such as deterministic all-optical quantum computation, dense
coding and teleportation.Comment: Corrected typo
Superluminal optical pulse propagation in nonlinear coherent media
The propagation of light-pulse with negative group-velocity in a nonlinear
medium is studied theoretically. We show that the necessary conditions for
these effects to be observable are realized in a three-level -system
interacting with a linearly polarized laser beam in the presence of a static
magnetic field. In low power regime, when all other nonlinear processes are
negligible, the light-induced Zeeman coherence cancels the resonant absorption
of the medium almost completely, but preserves the dispersion anomalous and
very high. As a result, a superluminal light pulse propagation can be observed
in the sense that the peak of the transmitted pulse exits the medium before the
peak of the incident pulse enters. There is no violation of causality and
energy conservation. Moreover, the superluminal effects are prominently
manifested in the reshaping of pulse, which is caused by the
intensity-dependent pulse velocity. Unlike the shock wave formation in a
nonlinear medium with normal dispersion, here, the self-steepening of the pulse
trailing edge takes place due to the fact that the more intense parts of the
pulse travel slower. The predicted effect can be easily observed in the well
known schemes employed for studying of nonlinear magneto-optical rotation. The
upper bound of sample length is found from the criterion that the pulse
self-steepening and group-advance time are observable without pulse distortion
caused by the group-velocity dispersion.Comment: 16 pages, 7 figure