Quantum Cloning Machines with Phase-Conjugate Input Modes
Nicolas J. Cerf, S. Iblisdir · Physical Review Letters · 2001
A quantum cloning machine is introduced that yields $M$ identical optimal clones from $N$ replicas of a coherent state and ${N}^{\ensuremath{'}}$ replicas of its phase conjugate. It also optimally produces ${M}^{\ensuremath{'}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}M+N}^{\ensuremath{'}}\ensuremath{-}N$ phase-conjugate clones at no cost. For well chosen ratios ${N}^{\ensuremath{'}}/N$, this machine is shown to provide better cloning fidelities than the standard $({N+N}^{\ensuremath{'}})\ensuremath{\rightarrow}M$ cloner. The special cases of the optimal balanced cloner $({N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}N}^{\ensuremath{'}})$ and optimal measurement $(M\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\infty})$ are investigated.