Europhys. Lett.
Volume 75, Number 2, July 2006
Page(s) 195 - 201
Section General
Published online 16 June 2006
Europhys. Lett., 75 (2), pp. 195-201 (2006)
DOI: 10.1209/epl/i2006-10105-x

Superbroadcasting of conjugate quantum variables

G. 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 $N \geq 2$ 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. $M\leq N$), 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.

03.65.-w - Quantum mechanics.
03.67.-a - Quantum information.

© EDP Sciences 2006