Semi-Device-Independent Certification of Causal Nonseparability with Trusted Quantum Inputs

Abstract

While the standard formulation of quantum theory assumes a fixed background causal structure, one can relax this assumption within the so-called process matrix framework. Remarkably, some processes, termed causally nonseparable, are incompatible with a definite causal order. We explore a form of certification of causal nonseparability in a semi-device-independent scenario where the involved parties receive trusted quantum inputs, but whose operations are otherwise uncharacterised. Defining the notion of causally nonseparable distributed measurements, we show that certain causally nonseparable processes which cannot violate any causal inequality, including the canonical example of the quantum switch, can generate noncausal correlations in such a scenario. Moreover, by imposing some further natural structure to the untrusted operations, we show that all bipartite causally nonseparable process matrices can be certified with trusted quantum inputs.

arXiv comment6 + 17 pages, 1 figure. v2: updated to published version

References in corpus (27)

• Quantum correlations with no causal order
• Quantum computations without definite causal structure
• Theoretical framework for quantum networks
• Quantum Circuits Architecture
• Experimental Superposition of Orders of Quantum Gates
• Computational advantage from quantum-controlled ordering of gates
• Experimental Verification of an Indefinite Causal Order
• Perfect discrimination of no-signalling channels via quantum superposition of causal structures
• All Entangled Quantum States Are Nonlocal
• Indefinite Causal Order in a Quantum Switch
• Exponential Communication Complexity Advantage from Quantum Superposition of the Direction of Communication
• Witnessing causal nonseparability
• Measurement-Device-Independent Entanglement Witnesses for All Entangled Quantum States
• Causal and causally separable processes
• Experimental transmission of quantum information using a superposition of causal orders
• Experimental Quantum Switching for Exponentially Superior Quantum Communication Complexity
• The simplest causal inequalities and their violation
• Device-independent entanglement certification of all entangled states
• Quantum circuits with classical versus quantum control of causal order
• Multipartite Causal Correlations: Polytopes and Inequalities
• Witnesses of causal nonseparability: an introduction and a few case studies
• On the definition and characterisation of multipartite causal (non)separability
• Measurement-device-independent entanglement and randomness estimation in quantum networks
• A channel-based framework for steering, non-locality and beyond
• Causally nonseparable processes admitting a causal model
• Semi-device-independent certification of indefinite causal order
• Self-testing and certification using trusted quantum inputs

Cited by in corpus (7)

• Experimental Aspects of Indefinite Causal Order in Quantum Mechanics
• Semi-device-independent certification of indefinite causal order in a photonic quantum switch
• Higher-order Process Matrix Tomography of a passively-stable Quantum SWITCH
• Network-Device-Independent Certification of Causal Nonseparability
• Emergent non-Markovianity and dynamical quantification of the quantum switch
• Sequential device-independent certification of indefinite causal order
• No quantum advantage for violating fixed-order inequalities?