Pauli cloning of a quantum Bit

A family of asymmetric quantum cloning machines is introduced that produce two approximate copies of a single quantum bit, each copy emerging from a Pauli channel. A no-cloning inequality is derived, describing the balance between the quality of the copies. The Pauli cloning machine is also shown to put a limit on the quantum capacity of Pauli channels.

Cloning of continuous quantum variables

The cloning of quantum variables with continuous spectra is analyzed. A Gaussian quantum cloning machine is exhibited that copies equally well the states of two conjugate variables such as position and momentum. It also duplicates all coherent states with a fidelity of 2/3. More generally, the copies are shown to obey a no-cloning Heisenberg-like uncertainty relation.

Classical teleportation of a quantum Bit

Classical teleportation is defined as a scenario where the sender is given the classical description of an arbitrary quantum state while the receiver simulates any measurement on it. This scenario is shown to be achievable by transmitting only a few classical bits if the sender and receiver initially share local hidden variables. Specifically, a communication of 2.19 bits is sufficient on average for the classical teleportation of a qubit, when restricted to von Neumann measurements. The generalization to positive-operator-valued measurements is also discussed.