How to Construct Random Unitaries

The existence of pseudorandom unitaries (PRUs) -- efficient quantum circuits that are computationally indistinguishable from Haar-random unitaries -- has been a central open question, with significant implications for cryptography, complexity theory, and fundamental physics. In this work, we close t...

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Bibliographic Details
Main Authors Ma, Fermi, Huang, Hsin-Yuan
Format Journal Article
LanguageEnglish
Published 13.10.2024
Subjects
Computer Science - Computation and Language
Computer Science - Computational Complexity
Mathematics - Mathematical Physics
Physics - Mathematical Physics
Physics - Quantum Physics
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Summary:The existence of pseudorandom unitaries (PRUs) -- efficient quantum circuits that are computationally indistinguishable from Haar-random unitaries -- has been a central open question, with significant implications for cryptography, complexity theory, and fundamental physics. In this work, we close this question by proving that PRUs exist, assuming that any quantum-secure one-way function exists. We establish this result for both (1) the standard notion of PRUs, which are secure against any efficient adversary that makes queries to the unitary $U$, and (2) a stronger notion of PRUs, which are secure even against adversaries that can query both the unitary $U$ and its inverse $U^\dagger$. In the process, we prove that any algorithm that makes queries to a Haar-random unitary can be efficiently simulated on a quantum computer, up to inverse-exponential trace distance.
DOI:10.48550/arxiv.2410.10116