  We demonstrate an optically controlled waveplate at ~1323 nm using the
5S1/2-5P1/2-6S1/2 ladder transition in a Rb vapor cell. The lower leg of the
transitions represents the control beam, while the upper leg represents the
signal beam. We show that we can place the signal beam in any arbitrary
polarization state with a suitable choice of polarization of the control beam.
Specifically, we demonstrate a differential phase retardance of ~180 degrees
between the two circularly polarized components of a linearly polarized signal
beam. We also demonstrate that the system can act as a Quarter Wave plate. The
optical activity responsible for the phase retardation process is explained in
terms of selection rules involving the Zeeman sublevels. As such, the system
can be used to realize a fast Stokesmetric Imaging system with a speed of
nearly 5 MHz. When implemented using a tapered nano fiber embedded in a vapor
cell, this system can be used to realize an ultra-low power all-optical switch
as well as a Quantum Zeno Effect based all-optical logic gate by combining it
with an optically controlled polarizer, previously demonstrated by us. We
present numerical simulations of the system using a comprehensive model which
incorporates all the relevant Zeeman sub-levels in the system, using a novel
algorithm recently developed by us for efficient computation of the evolution
of an arbitrary large scale quantum system.
