Preserving photon qubits in an unknown quantum state with Knill   Dynamical Decoupling - Towards an all optical quantum memory
  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. 
Manish K. Gupta, Erik J. Navarro, Todd A. Moulder, Jason D. Mueller,   Ashkan Balouchi, Katherine L. Brown, Hwang Lee and Jo...
quant-ph