Periodicity for space-inhomogeneous quantum walks on the cycle
  In this paper, we consider periodicity for space-inhomogeneous quantum walks on the cycle. For isospectral coin cases, we propose a spectral analysis. Based on the analysis, we extend the result for periodicity for Hadamard walk to some isospectral coin cases. For non-isospectral coin cases, we consider the the system that uses only one general coin at the origin and the identity coin at the other sites. In this case, we show that the periodicity of the general coin at the origin determines the periodicity for the whole system. 
Toshiyuki Arai, Choon-Lin Ho, Yusuke Ide, Norio Konno
quant-ph