The role of nonlocality in optical computing

John Caulfield, Shlomi Dolev

David A. B. Miller

J. D. Franson, T. B. Pittman

Jonathan Allcock, Harry Buhrman, Noah Linden

It has previously been shown that quantum nonlocality offers no benefit over classical correlations for performing a distributed task known as nonlocal computation. This is where separated parties must compute the value of a function without individually learning anything about the inputs. We show that giving the parties some knowledge of the inputs, however small, is sufficient to ``unlock'' the power of quantum mechanics to outperform classical mechanics. This role of information held locally gives insight into the general question of when quantum nonlocality gives an advantage over classical physics. Our results also reveal an interesting feature of the nonlocality embodied in the celebrated task of Clauser, Horne, Shimony, and Holt.

Sverre Gullikstad Johnsen

Samuraí Brito, Bárbara Amaral, Rafael Chaves

Measurements performed on distant parts of an entangled quantum state can generate correlations incompatible with classical theories respecting the assumption of local causality. This is the phenomenon known as quantum nonlocality that, apart from its fundamental role, can also be put to practical use in applications such as cryptography and distributed computing. Clearly, developing ways of quantifying nonlocality is an important primitive in this scenario. Here, we propose to quantify the nonlocality of a given probability distribution via its trace distance to the set of classical correlations. We show that this measure is a monotone under the free operations of a resource theory and, furthermore, that it can be computed efficiently with a linear program. We put our framework to use in a variety of relevant Bell scenarios also comparing the trace distance to other standard measures in the literature.