Difficulty of distinguishing product states locally

Abstract

Non-locality without entanglement is a rather counter-intuitive phenomenon in which information may be encoded entirely in product (unentangled) states of composite quantum systems in such a way that local measurement of the subsystems is not enough for optimal decoding. For simple examples of pure product states, the gap in performance is known to be rather small when arbitrary local strategies are allowed. Here we restrict to local strategies readily achievable with current technology; those requiring neither a quantum memory nor joint operations. We show that, even for measurements on pure product states there can be a large gap between such strategies and theoretically optimal performance. Thus even in the absence of entanglement physically realizable local strategies can be far from optimal for extracting quantum information.

arXiv comment5 pages, 1 figure

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• Genuinely Nonlocal Product Bases: Classification and Entanglement Assisted Discrimination
• Strong Quantum Nonlocality without Entanglement in Multipartite Quantum Systems
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• Multi-partite subspaces containing no locally inaccessible information
• Coherence measure of ensembles with nonlocality without entanglement
• Novel methods to construct nonlocal sets of orthogonal product states in arbitrary bipartite high-dimensional system
• Measurement disturbance tradeoffs in three-qubit unsupervised quantum classification
• Conclusive Local State Marking: More Nonlocality With No Entanglement