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SYSA: Quantum state analysis and estimation

SYSA 2: Quantum state analysis and estimation II

SYSA 2.3: Invited Talk

Tuesday, March 14, 2006, 15:00–15:30, HVI

Superbroadcasting of mixed states — •Chiara Macchiavello — Dipartimento di Fisica No-dqA. VoltaNo-dq, Via Bassi 6, 27100 Pavia (Italy)

No-dqBroadcastingNo-dq, namely distributing information over many users, suffers in-principle limitations when the information is quantum. For pure states ideal broadcasting coincides with the so-called No-dqquantum cloningNo-dq, which is forbidden by the no-cloning theorem for pure states drawn from a nonorthogonal set. For mixed states the no-broadcasting theorem says that perfect broadcasting from an input state drawn from a set of two noncommuting density operators to two output states cannot be achieved. We prove that this theorem cannot be generalized to more than a single input copy. Moreover, we present the phenomenon of superbroadcasting, where it is possible to purify the input states while broadcasting. We also discuss the relations between optimal superbroadcasting and other tasks of interest in quantum information.