No-compressing of quantum phase information
  We raise a general question of quantum information theory whether the quantum phase information can be compressed and retrieved. A general qubit contains both amplitude and phase information, while an equatorial qubit contains only a phase information. We study whether it is possible to compress the phase information of n equatorial qubits into m general qubits with m being less than n, and still those information can be retrieved perfectly. We prove that this process is not allowed by quantum mechanics. 
Yi-Nan Wang, Han-Duo Shi, Li Jing, Zhao-Xi Xiong, Jin Lei, Liang-Zhu   Mu and Heng Fan
quant-ph