Europhys. Lett.
Volume 75, Number 1, July 2006
Page(s) 1 - 7
Section General
Published online 09 June 2006
Europhys. Lett., 75 (1), pp. 1-7 (2006)
DOI: 10.1209/epl/i2005-10598-7

Nonlocal effect of a bipartite system induced by local cyclic operation

Li-Bin Fu

Institute of Applied Physics and Computational Mathematics P.O. Box 8009 (28), 100088 Beijing, PRC and Max-Planck-Institute for the Physics of Complex Systems Nöthnitzer Strasse 38, 01187 Dresden, Germany

received 6 July 2005; accepted in final form 17 May 2005
published online 9 June 2006

The state of a bipartite system may be changed by a cyclic operation applied on one of its subsystems. The change is a nonlocal effect, and can be detected only by measuring the two parts jointly. By employing the Hilbert-Schmidt metric, we can quantify such nonlocal effects via measuring the distance between the initial and final state. We show that this nonlocal property can be manifested not only by entangled states but also by the disentangled states which are classically correlated. Furthermore, we study the effect for the system of two qubits in detail. It is interesting that the nonlocal effect of disentangled states is limited by $1/
\sqrt{2}$, while the entangled states can exceed this limit and reach 1 for maximally entangled states.

03.65.Ud - Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.).
03.67.-a - Quantum information.

© EDP Sciences 2006