Dynamics of relaxation, decoherence and entropy of a qubit in   anisotropic photonic crystals
  We study the quantum dynamics of relaxation, decoherence and entropy of a qubit embedded in an anisotropic photonic crystal (PhC) through fractional calculus. These quantum measurements are investigated by analytically solving the fractional Langevin equation. The qubit with frequency lying inside the photonic band gap (PBG) exhibits the preserving behavior of energy, coherence and information amount through the steady values of excited-state probability, polarization oscillation and von Neumann entropy. This preservation does not exist in the Markovian system with qubit frequency lying outside the PBG region. These accurate results are based on the appropriate mathematical method of fractional calculus and reasonable inference of physical phenomena. 
Jing-Nuo Wu, Hung-Kuang Chen, Wen-Feng Hsieh, and Szu-Cheng Cheng
quant-ph cond-mat.other physics.optics