Quantum steering beyond instrumental causal networks

Abstract

We theoretically predict, and experimentally verify with entangled photons, that outcome communication is not enough for hidden-state models to reproduce quantum steering. Hidden-state models with outcome communication correspond, in turn, to the well-known instrumental processes of causal inference but in the 1-sided device-independent (1S DI) scenario of one black-box measurement device and one well-characterised quantum apparatus. We introduce 1S-DI instrumental inequalities to test against these models, with the appealing feature of detecting entanglement even when communication of the black box's measurement outcome is allowed. We find that, remarkably, these inequalities can also be violated solely with steering, i.e. without outcome communication. In fact, an efficiently-computable formal quantifier -- the robustness of non-instrumentality -- naturally arises; and we prove that steering alone is enough to maximize it. Our findings imply that quantum theory admits a stronger form of steering than known until now, with fundamental as well as practical potential implications.

7+4 pages, 3 figures; accepted for publication in Physical Review Letters

References in corpus (11)

• Einstein-Podolsky-Rosen steering provides the advantage in entanglement-assisted subchannel discrimination with one-way measurements
• The Communication Cost of Simulating Bell Correlations
• Beyond Bell's Theorem: Correlation Scenarios
• Information-Theoretic Implications of Quantum Causal Structures
• Theory-independent limits on correlations from generalised Bayesian networks
• Inferring causal structure: a quantum advantage
• A unifying framework for relaxations of the causal assumptions in Bell's theorem
• Quantum violation of an instrumental test
• Instrumentality Tests Revisited
• Nonlocality free wirings and the distinguishability between Bell boxes
• Bell scenarios with communication

Cited by in corpus (10)

• Fermionic steering and its monogamy relations in Schwarzschild spacetime
• Quantifying causal influences in the presence of a quantum common cause
• Distributed sampling, quantum communication witnesses, and measurement incompatibility
• Bipartite post-quantum steering in generalised scenarios
• Quantum Causal Inference with Extremely Light Touch
• Detecting quantum steering in networks
• No nonlocal advantage of quantum coherence beyond quantum instrumentality
• The rank of contextuality
• Tripartite quantum steering in Schwarzschild spacetime
• A hierarchy of semidefinite programs for generalised Einstein-Podolsky-Rosen scenarios