Abstract
We present a formalization of several fundamental notions and results from Quantum Information theory in the proof assistant Isabelle/HOL, including density matrices and projective measurements, along with the proof that the local hidden-variable hypothesis advocated by Einstein to model quantum mechanics cannot hold. The proof of the latter result is based on the so-called CHSH inequality, and it is the violation of this inequality that was experimentally evidenced by Aspect, who earned the Nobel Prize in 2022 for his work. We also formalize various results related to the violation of the CHSH inequality, such as Tsirelson’s bound, which quantifies the amount to which this inequality can be violated in a quantum setting.


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Since then, it has been proven that this phenomenon is in no contradiction with the theory of relativity and does not imply faster-than-light communication.
The superscript is omitted when there is no confusion.
Lemma
.
As mentioned in [33], it would be more precise to write in a causally disconnected manner meaning that no information can be transmitted between Alice and Bob. This is ensured in practice by physically separating them, assuming that information cannot travel faster than light.
Including in the original paper on the CHSH inequality [15].
Note that these notions are formalized in a general setting that makes no mention of bipartite states or tensor products.
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Acknowledgements
This work benefited from the funding program “Plan France 2030” (ANR-22-PETQ-0007) of the French National Research Agency.
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Echenim, M., Mhalla, M. A Formalization of the CHSH Inequality and Tsirelson’s Upper-bound in Isabelle/HOL. J Autom Reasoning 68, 2 (2024). https://doi.org/10.1007/s10817-023-09689-9
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DOI: https://doi.org/10.1007/s10817-023-09689-9