We review the basic theory of approximate quantum cloning for discrete variables and some schemes for implementing quantum cloning machines.Several types of approximate quantum clones and their expansive quantum clones are introduced.As for the implementation of quantum cloning machines,we review some design methods and recent experimental results.
We review the basic theory of approximate quantum cloning for discrete variables and some schemes for implementing quantum cloning machines. Several types of approximate quantum clones and their expansive quantum clones are intro- duced. As for the implementation of quantum cloning machines, we review some design methods and recent experimental results.