Rise of conditionally clean ancillae for efficient quantum circuit constructions
Tanuj Khattar, Craig Gidney · 2025 · Quantum 9, 1752
| 编号 QQFT026 | 主题 量子傅里叶变换 | 链接 DOI 10.22331/q-2025-05-21-1752 |
摘要
摘要保留原文（英文）
摘要取自 Crossref 出版方元数据，未作翻译，以保证与原文一致。
We introduce conditionally clean ancilla qubits, a new quantum resource, recently explored by a prior work, that bridges the gap between traditional clean and dirty ancillae. Like dirty ancillae, they begin and end in an unknown state and can be borrowed from existing system qubits, avoiding the space overhead of explicit qubit allocation. Like clean ancillae, they can be treated as initialized in a known state within specific computations, thus avoiding the overhead of toggle detection required for dirty ancillae. We present new circuit constructions leveraging conditionally clean ancillae to achieve lower gate counts and depths, particularly with limited ancilla availability. Specifically, we provide constructions for: (a) -controlled NOT using Toffolis and depth given 2 clean ancillae. (b) -qubit incrementer using Toffolis given clean ancillae. (c) -qubit quantum-classical comparator using Toffolis given clean ancillae. (d) unary iteration over using Toffolis given clean ancillae. (e) unary iteration via skew tree over using Toffolis given dirty ancillae. We also introduce laddered toggle detection, a technique to replace clean ancillae with dirty ancillae in all our constructions, incurring a 2x Toffoli gate overhead. Our results demonstrate that conditionally clean ancillae are a valuable tool for quantum circuit design, especially in the resource-constrained early fault-tolerant era.
读法提示
原文在该句中带一处引用标记，所引前作未包含在本轮取到的出版方元数据内，因此此处记为 “a prior work”，未替换成任何具体作者或编号。
另一个读法提示：本条目的原语（多控 NOT、递增器、比较器、一元迭代）都不是 QFT 线路，它改善的是辅助比特与门计数的口径。引用时应按本站合成与成本的三栏归类，而不是当成 QFT 的 T 数改进。
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