Quantum information scrambling is a unitary process that destroys local correlations and spreads information throughout the system, effectively hiding it in nonlocal degrees of freedom. In principle, unscrambling this information is possible with perfect knowledge of the unitary dynamics[arXiv:1710.03363]. However, this work demonstrates that even without previous knowledge of the internal dynamics, information can be efficiently decoded from an unknown scrambler by monitoring the outgoing information of a local subsystem. Surprisingly, we show that scramblers with unknown internal dynamics, which are rapidly mixing but not fully chaotic, can be decoded using Clifford decoders. The essential properties of a scrambling unitary can be efficiently recovered, even if the process is exponentially complex. Specifically, we establish that a unitary operator composed of $t$ non-Clifford gates admits a Clifford decoder up to $t\le n$.

翻译：量子信息扰乱是一个幺正过程，它破坏局域关联并将信息扩散至整个系统，从而将其隐藏于非定域自由度中。理论上，若能完美掌握幺正动力学，即可解开此类信息[arXiv:1710.03363]。然而，本研究证明，即便对内部动力学一无所知，通过监测局域子系统的出射信息，仍能从未知扰乱器中高效解码出量子信息。令人惊讶的是，我们表明具有未知内部动力学的扰乱器——尽管快速混合但未完全混沌——可通过 Clifford 解码器实现解码。即使该过程具有指数级复杂度，扰乱幺正的核心理性质仍能被有效恢复。具体而言，我们证明一个由 $t$ 个非 Clifford 门构成的幺正算符在 $t\le n$ 的条件下可适配 Clifford 解码器。