Semidefinite tests for quantum network topologies

Understand

Quantum networks play a major role in long-distance communication, quantum cryptography, clock synchronization, and distributed quantum computing.

• Generally, these protocols involve many independent sources sharing entanglement among distant parties that, upon measuring their systems, generate correlations across the network.
• The question of which correlations a given quantum network can give rise to, remains almost uncharted.
• Here we show that constraints on the observable covariances, previously derived for the classical case, also hold for quantum networks.