  While exact cloning of an unknown quantum state is prohibited by the
linearity of quantum mechanics, approximate cloning is possible and has been
used, e.g., to derive limits on the security of quantum communication
protocols. In the case of asymmetric cloning, the information from the input
state is distributed asymmetrically between the different output states. Here,
we consider asymmetric phase-covariant cloning, where the goal is to optimally
transfer the phase information from a single input qubit to different output
qubits. We construct an optimal quantum cloning machine for two qubits that
does not require ancilla qubits and implement it on an NMR quantum information
processor.
