Implementation of quantum operations on single photon qudits
  We show that a general linear transformation from one single photon qudit to another, the dimension of which can be either equal or unequal to that of the first one, can be implemented by linear optics. As an application of the scheme we elaborate a method to deterministically realize any finite-element Positive Operator Value Measure (POVM) on single photon signals, which is also generalizable to any quantum system in principle. 
Bing He, J\'anos A. Bergou and Zhiyong Wang