Superbroadcasting of conjugate quantum variables

D'Ariano, Giacomo M.; Perinotti, Paolo; Sacchi, Massimiliano F.

Superbroadcasting of conjugate quantum variables

Authors

D'Ariano, Giacomo M.

Perinotti, Paolo

Sacchi, Massimiliano F.

Description

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 N>=2 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. M<=N), 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.
7 pages, 1 eps figures. Accepted for publication on Europhysics Letters