Beating no-go theorems by engineering defects in quantum spin models

Abstract

Diverse no-go theorems exist, ranging from no-cloning to monogamies of quantum correlations and Bell inequality violations, which restrict the processing of information in the quantum world. In a multipartite scenario, monogamy of Bell inequality violation and the exclusion principle of dense coding are such theorems which impede the ability of the system to have quantum advantage between all its parts. In ordered spin systems, the twin restrictions of translation invariance and monogamy of quantum correlations, in general, enforce the bipartite states to be neither Bell inequality violating nor dense codeable. We show that it is possible to conquer these constraints imposed by quantum mechanics in ordered systems by introducing quenched impurities in the system while still retaining translation invariance at the physically relevant level of disorder-averaged observables.