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Optimal universal quantum cloning and state estimation
D. Bruss, A. Ekert, C. Macchiavello
We derive a tight upper bound for the fidelity of a universal N to M qubit cloner, valid for any M \geq N, where the output of the cloner is required to be supported on the symmetr…
Quantum Algorithms Revisited
Richard Cleve, Artur Ekert, Chiara Macchiavello +1
Quantum computers use the quantum interference of different computational paths to enhance correct outcomes and suppress erroneous outcomes of computations. A common pattern underp…
On the Improvement of Frequency Stardards with Quantum Entanglement
S. F Huelga, C. Macchiavello, T. Pellizzari +3
The optimal precision of frequency measurements in the presence of decoherence is discussed. We analyze different preparations of n two level systems as well as different measureme…
Optimal Universal and State-Dependent Quantum Cloning
D. Bruss, D. P. DiVincenzo, A. Ekert +3
We establish the best possible approximation to a perfect quantum cloning machine which produces two clones out of a single input. We analyze both universal and state-dependent clo…