Quantitative quantum soundness for all multipartite compiled nonlocal games

Mon, 09 Mar 2026 00:00:00 +0000

Compiled nonlocal games transfer the power of Bell-type multi-prover tests into a single-device setting by replacing spatial separation with cryptography. Concretely, the KLVY compiler (STOC'23) maps any multi-prover game to an interactive single-prover protocol, using quantum homomorphic encryption. A crucial security property of such compilers is quantum soundness, which ensures that a dishonest quantum prover cannot exceed the original game’s quantum value. For practical cryptographic implementations, this soundness must be quantitative, providing concrete bounds, rather than merely asymptotic. While quantitative quantum soundness has been established for the KLVY compiler in the bipartite case, it has only been shown asymptotically for multipartite games. This is a significant gap, as multipartite nonlocality exhibits phenomena with no bipartite analogue, and the difficulty of enforcing space-like separation makes single-device compilation especially compelling. This work closes this gap by showing the quantitative quantum soundness of the KLVY compiler for all multipartite nonlocal games. On the way, we introduce an NPA-like hierarchy for quantum instruments and prove its completeness, thereby characterizing correlations from operationally-non-signaling sequential strategies. We further develop novel geometric arguments for the decomposition of sequential strategies into their signaling and non-signaling parts, which might be of independent interest.

Xiangling Xu - Characterizing quantum bilocal network scenario with generalized NPA hierarchies

Fri, 31 Jan 2025 00:00:00 +0000

Characterizing quantum bilocal network scenario with generalized NPA hierarchies

This seminar, given by Xiangling Xu, will happend on 31 January 2025, at 15:0. It will take place in Room Not specified.

Find a map of the campus here.

Abstract

Characterizing quantum correlations is a fundamental task in the study of quantum information theory. In the standard Bell scenario, where the correlations are established by a single source, the seminal work [Navascúes et al., 2008] presents a convergent hierarchy that provides an outer approximation, which can be formulated as a problem solvable by computers.

In the more general networks scenarios, however, the correlations are due to multiple independent quantum sources. This necessitates a generalization of the NPA hierarchy. Based on [Renou, Xu, Ligthard, 2022], this talk focuses on the simplest quantum network, the bilocal scenario, where two independent quantum sources exist: one shared between Alice and Bob, and the other between Bob and Charlie. It will discuss two convergent generalizations of the NPA hierarchy in this context, demonstrating that the bilocal scenario is completely understood from the algebraic/Heisenberg perspective.

Xiangling Xu | LIP6 - QI Team

Quantitative quantum soundness for all multipartite compiled nonlocal games

Xiangling Xu - Characterizing quantum bilocal network scenario with generalized NPA hierarchies

Characterizing quantum bilocal network scenario with generalized NPA hierarchies

Abstract