  The implementation of polarization-based quantum communication is limited by
signal loss and decoherence caused by the birefringence of a single-mode fiber.
We investigate the Knill dynamical decoupling scheme, implemented using
half-wave plates, to minimize decoherence and show that a fidelity greater than
$99\%$ can be achieved in absence of rotation error and fidelity greater than
$96\%$ can be achieved in presence of rotation error. Such a scheme can be used
to preserve any quantum state with high fidelity and has potential application
for constructing all optical quantum delay line, quantum memory, and quantum
repeater.

Quantum Physics