A recent theoretical study has presented a framework for comprehending nonlocality, a characteristic essential for quantum networks to perform operations beyond the capabilities of standard communication technology. This study, published in Physical Review Letters, introduces a new classification scheme for quantum nonlocality by adapting techniques from quantum computing theory. By doing so, the researchers were able to unify previous studies on nonlocality into a common framework and establish the necessary conditions for creating systems with strong quantum correlations.

Nonlocality arises from entanglement, a phenomenon in which quantum objects maintain strong connections even when separated by vast distances. When entangled objects are used for quantum operations, the results exhibit statistical correlations that cannot be explained by classical means, leading to nonlocal effects. To ensure that a quantum network can perform genuinely quantum functions, it must possess a certain degree of nonlocality, although the phenomenon itself remains poorly understood.

To facilitate the study of nonlocality, the project lead, Professor Eric Chitambar, and physics graduate student Amanda Gatto Lamas employed the formalism of quantum resource theory. By treating nonlocality as a manageable “resource,” their framework allowed them to view previous studies on nonlocality as different instances of the same concept, albeit with varying restrictions on the availability of the resource. This approach enabled them to prove their main result, which states that nonlocality can only be achieved using a limited set of quantum operations.

Gatto Lamas explained that their result is akin to the Gottesman-Knill theorem in quantum computing, as it establishes the specific operations required to surpass classical capabilities in a quantum network, just as the Gottesman-Knill theorem defines the necessary conditions for a quantum computer to outperform a classical one.

Chitambar anticipates that this framework will not only aid in developing criteria for evaluating the quality of a quantum network based on its degree of nonlocality but also in expanding the concept itself. He suggests that while there is a relatively good understanding of the nonlocality that can emerge between two parties, for a quantum network composed of many connected parties, there may be a global property that cannot be reduced to individual pairs within the network. This global property might depend on the overall structure of the network, presenting an avenue for further exploration.

Source: University of Illinois Grainger College of Engineering