Broadcasting of non-locality

TL;DR

This paper investigates the limitations of broadcasting quantum nonlocality and steering via local quantum cloning, showing that such nonlocal correlations cannot be broadcasted using universal Buzek-Hillery cloners, especially for two and three qubit systems.

Contribution

It demonstrates that local quantum cloning cannot broadcast nonlocality and steering, providing new insights into the fundamental restrictions of quantum correlation distribution.

Findings

Nonlocality cannot be broadcasted using local quantum cloning.

Some steerable states become unsteerable after cloning.

Genuine tripartite nonlocality cannot be broadcasted with universal BH cloners.

Abstract

Bell nonlocality and steering are archetypal characteristics of quantum mechanics that mark a significant departure from conventional classical notions. They basically refer to the presence of quantum correlations between separated systems which violate a nonlocal inequality, the violation otherwise not possible if we restrict ourselves only to classical correlations. In view of the importance of such unique correlations one may be interested to generate more states exhibiting nonlocality starting from a few, a protocol which is termed as broadcasting. However, in the present submission, we show using universal Buzek-Hillary(BH) quantum cloning machine that, if one restricts to broadcasting through local quantum cloning, then such nonlocality cannot be broadcasted. Our study is done in the purview of the Bell-CHSH inequality and the CJWR (E.G.Cavalcanti,S.J. Jones,H.M Wiseman and M.D. Reid, Phys.Rev.A 80,032112(2009)) steering inequality. It is observed that when number of measurement settings is greater than 6, some of the output states are steerable after the application of local optimal B-H cloners. We find that, under some restrictions, if the Werner and Bell diagonal states are subjected to such procedures, then the resultant state is rendered unsteerable. We extend this study to three qubit systems and find that genuine tripartite nonlocality cannot be broadcasted using universal BH local quantum cloners, when we consider the Svetlichny's inequality. For two qubit systems, we have considered $10^5$ simulated general local unitaries over Werner and Bell-diagonal states and find that for none of these states broadcasting on nonlocality and 3-steerability is possible.