Superbroadcasting of conjugate quantum variablesG. M. D'Ariano1, P. Perinotti1 and M. F. Sacchi1, 2
1 Dipartimento di Fisica "A. Volta" and CNISM - via Bassi 6, I-27100 Pavia, Italy
2 CNR - Istituto Nazionale per la Fisica della Materia, Unità di Pavia - Italy
received 7 April 2006; accepted in final form 29 May 2006
published online 16 June 2006
We consider the problem of broadcasting arbitrary states of radiation modes from N to M >N copies by a map that preserves the average value of the field and optimally reduces the total noise in conjugate variables. For the broadcasting can be achieved perfectly, and for sufficiently noisy input states one can even purify the state while broadcasting-the so-called superbroadcasting. For purification (i.e. ), the reduction of noise is independent of M. Similar results are proved for broadcasting with phase-conjugation. All the optimal maps can be implemented by linear optics and linear amplification.
03.65.-w - Quantum mechanics.
03.67.-a - Quantum information.
© EDP Sciences 2006