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Sum-of-squares decompositions for a family of CHSH-like inequalities and their application to self-testing

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arxiv 1504.06960 v1 pith:UNH4EYXA submitted 2015-04-27 quant-ph

Sum-of-squares decompositions for a family of CHSH-like inequalities and their application to self-testing

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keywords decompositionsexpressionsquantumalgebraicapplicationbellchshphys
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We introduce two families of sum-of-squares (SOS) decompositions for the Bell operators associated with the tilted CHSH expressions introduced in Phys. Rev. Lett. 108, 100402 (2012). These SOS decompositions provide tight upper bounds on the maximal quantum value of these Bell expressions. Moreover, they establish algebraic relations that are necessarily satisfied by any quantum state and observables yielding the optimal quantum value. These algebraic relations are then used to show that the tilted CHSH expressions provide robust self-tests for any partially entangled two-qubit state. This application to self-testing follows closely the approach of Phys. Rev. A 87, 050102 (2013), where we identify and correct two non-trivial flaws.

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Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. No finite level of the NPA hierarchy is exact for the doubly-tilted CHSH functional near the critical tilt

    quant-ph 2026-07 conditional novelty 8.0

    No finite NPA level reproduces the quantum value of the doubly-tilted CHSH functional in any neighbourhood of the critical tilt; each level strictly overshoots with at least quadratic gap.

  2. A phase transition in the exactness of the NPA hierarchy at the critical doubly-tilted CHSH functional

    quant-ph 2026-07 conditional novelty 7.0

    For the doubly-tilted CHSH functional, the NPA hierarchy is exact at every level above the critical tilt and provably non-exact near it, a phase transition in exactness.

  3. Device-Independent Self-Testing of the Three-Qubit CCZ Hypergraph State

    quant-ph 2026-07 accept novelty 6.0

    The CCZ hypergraph state and its Pauli measurements can be device-independently self-tested from twenty correlators, and also from maximal violation of a specially constructed Bell inequality.