1203.3054 (Z. Gedik et al.)

Universal symmetric cloning: No-signalling and nonlinear quantum
mechanics    [PDF]

Z. Gedik, B. Çakmak

We present a pseudo-spin representation for universal symmetric 1-to-M cloning of qubits, including both linear and nonlinear evolutions. We derive a set of equations to be satisfied by the cloning transformation under the no-signalling condition, and find an expression for the fidelity. We further introduce the linearity constraint, and obtain the unique universal symmetric quantum cloning machine for "an arbitrary" fidelity. No-signalling condition alone leads to fidelities higher than those of the quantum machines, and the maximum value converges to 3/4 rather than the optimal quantum limit of 2/3. We introduce the "prime cloners" whose fidelities have multiplicative property and show that the infinite copy limit of the prime cloners is 1/2.

View original: http://arxiv.org/abs/1203.3054