Network-Device-Independent Certification of Causal Nonseparability
Hippolyte Dourdent, Alastair A. Abbott, Ivan \v{S}upi\'c, Cyril, Branciard

TL;DR
This paper introduces a method to certify the causal nonseparability of quantum processes, including the quantum switch, in a device-independent manner using observed correlations and untrusted operations.
Contribution
It provides the first device-independent certification method for causal nonseparability of processes with trusted quantum inputs, including the quantum switch.
Findings
Certifies causal nonseparability in a device-independent way
Includes certification of the quantum switch
Uses a network of untrusted operations for self-testing
Abstract
Causal nonseparability is the property underlying quantum processes incompatible with a definite causal order. So far it has remained a central open question as to whether any process with a clear physical realisation can violate a causal inequality, so that its causal nonseparability can be certified in a device-independent way, as originally conceived. Here we present a method solely based on the observed correlations, which certifies the causal nonseparability of all the processes that can induce a causally nonseparable distributed measurement in a scenario with trusted quantum input states, as defined in [Dourdent et al., Phys. Rev. Lett. 129, 090402 (2022)]. This notably includes the celebrated quantum switch. This device-independent certification is achieved by introducing a network of untrusted operations, allowing one to self-test the quantum inputs on which the effective…
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Taxonomy
TopicsQuantum Mechanics and Applications · Quantum Information and Cryptography · Quantum Computing Algorithms and Architecture
