  We present a unified universal quantum cloning machine, which combines
several different existing universal cloning machines together including the
asymmetric case. In this unified framework, the identical pure states are
projected equally into each copy initially constituted by input and one half of
the maximally entangled states. We show explicitly that the output states of
those universal cloning machines are the same. One importance of this unified
cloning machine is that the cloning procession is always the symmetric
projection which reduces dramatically the difficulties for implementation. Also
it is found that this unified cloning machine can be directly modified to the
general asymmetric case. Besides the global fidelity and the single-copy
fidelity, we also present all possible arbitrary-copy fidelities.

Quantum Physics