The Simplest Demonstrations of Quantum Nonlocality

Understand

We investigate the complexity cost of demonstrating the key types of nonclassical correlations --- Bell inequality violation, EPR-steering, and entanglement --- with independent agents, theoretically and in a photonic experiment.

• We show that the complexity cost exhibits a hierarchy among these three tasks, mirroring the recently-discovered hierarchy for how robust they are to noise.
• For Bell inequality violations, the simplest test is the well-known CHSH test, but for EPR-steering and entanglement the tests that involve the fewest number of detection patterns require non-projective measurements.
• The simplest EPR-steering requires a choice of projective measurement for one agent and a single non-projective measurement for the other, while the simplest entanglement test uses just a single non-projective measurement for each agent.