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：量子通道的叠加顺序已在理论和实验上被证明能够在量子通信领域带来前所未有的机遇。事实上，叠加顺序同样可应用于量子计算领域，这通过放宽传统量子计算中关于门操作需在明确定义因果顺序下执行的基本假设而实现。在此背景下，我们探讨了量子计算领域的一个基础性问题：单量子比特门的叠加顺序能否实现通用量子计算？如本文所示，这一关键问题的答案是明确的"肯定"。我们证明任何双量子比特受控量子门均可被确定性实现，其中包括能够单独实现通用量子计算的所谓Barenco门。