Robust self-testing of many-qubit states

Understand

We introduce a simple two-player test which certifies that the players apply tensor products of Pauli $\sigma_X$ and $\sigma_Z$ observables on the tensor product of $n$ EPR pairs.

• The test has constant robustness: any strategy achieving success probability within an additive $\varepsilon$ of the optimal must be $\mathrm{poly}(\varepsilon)$-close, in the appropriate distance measure, to the honest $n$-qubit strategy.
• The test involves $2n$-bit questions and $2$-bit answers.
• The key technical ingredient is a quantum version of the classical linearity test of Blum, Luby, and Rubinfeld.