Superposed orders of quantum channels have already been proved - both theoretically and experimentally - to enable unparalleled opportunities in the quantum communication domain. As a matter of fact, superposition of orders can be exploited within the quantum computing domain as well, by relaxing the (traditional) assumption underlying quantum computation about applying gates in a well-defined causal order. In this context, we address a fundamental question arising with quantum computing: whether superposed orders of single-qubit gates can enable universal quantum computation. As shown in this paper, the answer to this key question is a definitive "yes". Indeed, we prove that any two-qubit controlled quantum gate can be deterministically realized, including the so-called Barenco gate that alone enables universal quantum computation.

翻译：量子信道叠加序已在理论和实验上被证明能够在量子通信领域开启前所未有的机遇。事实上，通过放宽量子计算中关于门在明确定义因果顺序下应用的传统假设，叠加序同样可被应用于量子计算领域。在此背景下，我们探讨了一个量子计算中的根本性问题：单量子比特门的叠加序能否实现通用量子计算。本文表明，这一关键问题的答案是明确的"是"。事实上，我们证明了任意两量子比特受控量子门均可确定性实现，包括仅凭自身即可实现通用量子计算的所谓巴伦科门。